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COMPRESSED AIR SYSTEMS (CAS)

Learner Guide

TABLE OF CONTENTS INTRODUCTION PAGE 1 MODULE 1 "SYSTEMS OVERVIEW" CAS-1 PART 1: SYSTEMS AND SAFETY PAGE 3 SELF-TEST EXERCISE NO. 1 PAGE 9 CAS-1 PART 2: SAFETY WITH COMPRESSED -AIR PAGE 11 SELF-TEST EXERCISE NO. 2 PAGE 15 MODULE 2 "RECIPROCATING COMPRESSORS" CAS-2 PART 1: OPERATING PRINCIPLES PAGE 17 SELF-TEST EXERCISE NO. 1 PAGE 22 CAS-2 PART 2: MAINTENANCE TASKS PAGE 24 SELF-TEST EXERCISE NO. 2 PAGE 34 MODULE 3 “WET-SCREW ROTARY TYPE COMPRESSORS" CAS-3 PART 1: OPERATING PRINCIPLES PAGE 37 SELF-TEST EXERCISE NO. 1 PAGE 42 CAS-3 PART 2: MAINTENANCE TASKS PAGE 43 SELF-TEST EXERCISE NO. 2 PAGE 49 MODULE 4 " AIR-TREATMENT AND SYSTEM MAINTENANCE" CAS-4 PART 1: AIR-TREATMENT OVERVIEW PAGE 51 SELF-TEST EXERCISE NO. 1 PAGE 55 CAS-4 PART 2: SYSTEM MAINTENANCE PAGE 57 SELF-TEST EXERCISE NO. 2 PAGE 62

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COMPRESSED AIR SYSTEMS BASIC MAINTENANCE

INTRODUCTION This series of video assisted learning modules has been developed in order to assist you to understand common compressed air systems and to explain the procedures needed to perform the maintenance tasks required. This course has been designed primarily for equipment Operators and those tasked with performing basic "preventive maintenance" to compressed air systems. This is not a "pneumatics course" as we will be concerned with "air-supply" to the user point. STRUCTURE OF THIS SERIES This series has been designed in 4 separate modules each providing sufficient information to assist you in the workplace, but without "overloading" you with unnecessary information. The 4 modules are: CAS-1: An overview of compressed air systems and safety with compressed air. CAS-2: Reciprocating compressors. CAS-3: Rotary screw compressors. CAS-4: Airline system maintenance. Each module comprises two main references namely:

o A workbook section. o A video programme.

LEARNING PROCEDURE The procedure for learning is as follows:

1. Read the notes in the workbook and follow the instructions. 2. View the video section. 3. Complete a simple "self-test" exercise. 4. Practice doing the tasks that you have read and seen being demonstrated. (Under

the supervision of your Facilitator or Supervisor) THINGS THAT YOU'LL NEED If you want to get the best from this training session you'll need the following:

o Your normal "personal protective equipment" so you can work safely in the work place.

o Access to the compressed air system in your place of work. However this must always be with your Facilitator or Supervisor until you have proven yourself to be "competent".

o You'll also get a lot of help from the "Operators Manual" for any particular compressor that your plant uses.


SEQUENCE FOR LEARNING As this is not a "strict" system as we do not tell you what you must do or how to do it. We do however "recommend" that you begin your learning with module 1 (CAS-1). This will give you a basic understanding of the "why?" and "what?" of air systems and it will explain the basic "safety rules" that apply. When you have completed module 1 you will feel a lot more "at ease" with things. After this it doesn't matter in which order you attempt the modules as each can "stand alone". For example you may not need to know about "rotary screw compressors" if your plant only uses "reciprocating" types. However you may be interested in learning about rotary-screw types in which case the module will help you. TESTS Do not worry about "tests". There is no examination attached to this course and no one expects you to get "full marks" for anything. The tests in this course are all "self-tests" which means exactly what this says, you "test yourself'! When you've completed a "self-test" then check your answer by reviewing the material, either in the workbook or by reviewing the video section. If you enter a wrong answer, or can't answer a question, then simply go back over the lessons and look it up. The aim (objective) of this series is to help you do a job and to do it well and safely! Nobody wants you to "fail", so if you need to, you can do the lessons as many times as you want so that you get to "know" what to do and how to do it. Now it's over to you. Begin by turning the page and reading through the note for Module 1 (CAS-1).

TURN THE PAGE TO BEGIN MODULE CAS-1.


MODULE CAS-1 "SYSTEMS AND SAFETY"

PART 1 -SYSTEMS AN OVERVIEW OF COMPRESSED AIR SYSTEMS Compressed air is used in a variety of applications for example:

o To supply power to "pneumatic tools". o To operate power-cylinders and air-motors on production equipment. o To operate spray painting equipment. o To inflate tires on vehicle. o To operate cleaning apparatus / devices.

A basic understanding of the operating principles and the primary components of typical systems will assist you when you have to perform maintenance tasks on such systems. 1. BASIC COMPRESSED AIR SYSTEM

A compressed air system comprises all the necessary devices needed to generate and to supply air at a given pressure and flow-rate to the "working units".

A BASIC system comprises (most commonly) the following components:

o Compressor. o Receiver (or tank). o Supply-Lines (Pipe work).


Many industrial systems will also incorporate:

o After coolers. o Moisture separators. o Filters. o Lubricators.

SYSTEM COMPONENTS AND THEIR FUNCTIONS 1. THE COMPRESSOR

This is the unit responsible for "generating" air "pressure" and "air-flow" throughout the system. A compressor can be considered as being the "heart" of all compressed air systems. There are various types of compressors and you will probably have to deal with at least two types as you operate in various industries.

The two most commonly used types are: o Reciprocating compressors. o Rotary or "screw type" compressors.

A "Reciprocating Compressor" is easily identified by its "construction", as it looks very similar to an air-cooled engine. In fact it does share many similarities to the engine.


Reciprocating Type Compressor

You will find reciprocating compressors in all sorts of working environments, and are very commonly found in garages where they are needed for operating car-hoists, inflating tires and for cleaning components.

A "Rotary Screw" type compressor is a far more "compact" looking unit and these you will find are usually housed inside a neat "cabinet" looking encasement.

Typical Rotary Screw Unit

Rotary-screw compressors are more likely to be found in factories where "air" is needed to drive production machinery or power "robotic equipment" (Such as in a motor vehicle assembly operation). These units are designed to operate continuously and in some cases they are only shut down for maintenance!

2. RECEIVER Another name for this item is the "air-tank". The purpose of a receiver is to "store" air in its compressed state. Receivers are classified as "pressure vessels" and as such have to comply with (legislated) safety requirements. Sometimes the compressor is supported on top of the receiver, in which case the whole "package" is known as a "Tank Mounted unit". Some receivers are totally separate from the compressor and are called "free-standing units". Most industrial systems use "free-standing units" as these can be sited close to the "Working-units" thus minimising pressure drops, and permitting the noisy, heat-generating compressor to be housed away from the "working environment."


Tank-mounted Free standing

3. AIR-SUPPLY LINES (Mains) A "Main Supply Line" or "Air-Main" consists of the pipe-work required to distribute the air to various locations around the plant / factory. An Air-Main is normally constructed from steel piping. The pipe-work may be laid out in either a "branch-system", or in a "loop-system", or both depending on the needs of the operation.

At various locations along the supply line you will find connector-points, also known as "user-points" and "service-lines". These serve to accommodate a "connector" in


order to run a supply line to an individual "working device or to a piece of "air-driven machinery". Connector points are normally incorporated into a "drop-leg".

A drop-leg is simply a branch off the main supply line into which a "connecting coupling" is made. The connection is generally (should be) above the bottom of the drop leg. The extra space below the coupling point is intended to act as a "water trap" to collect "condensation". An "isolation valve" (or shut-off) is usually situated in the drop leg immediately "upstream" of the connector point / coupling. A "condensate" valve should be fitted at the bottom of a drop leg thus providing the means to "drain the condensate" regularly.

So far we have (very briefly) looked at the principle parts of a compressed air system but we need to look a little further because there are some important features in all systems known as "controls." 4. BASIC CONTROLS

At this time it must be understood that the purpose of the compressor is to generate the pressure and the flow of air necessary to operate various "working devices". The compressor will, if not "controlled', produce more pressure than is required or more than can be "safely" stored (held) in the receiver. All compressed-air systems must feature a "pressure-gauge" so that an operator or a technician can "monitor" the pressure within the system. You will most usually find a pressure gauge fitted directly into the receiver. This would be the "main pressure-gauge". Other gauges may also feature "down-stream" from the receiver or the compressor. These gauges are usually there to provide "Monitoring" of pressure entering a "working device".

Further "control devices are required along the air lines. 4.1. The first and most important control is the control of the compressors' output, and this can be done in various ways.

Most "smaller" compressors are controlled using a "Cut Out switch". This device is normally mounted in the compressors "supply or delivery line" to the receiver. When the air pressure reaches a certain value (typically around 8 kg/cm2) then the switch activates and "cuts out" the power supply to the electric motor that drives the compressor. As the air becomes used up (by the working units) the pressure drops in the receiver. At a certain pressure (typically at around 4 kg/cm2) the switch "resets or cuts-in" and power is restored to the compressor again. This simple arrangement is suitable for operations where the air use is low and infrequent.

Larger units are normally controlled by an "un-loader mechanism". This method does not stop the compressor from running but prevents it from "pumping air", by holding open the inlet valve or in some other way. (We need not be concerned about how this works at this time.)


4.2. The next vital "control device" is called the "safety-valve", sometimes called a "relief-valve" or a "release-valve".

This valve may be situated in any position on the receiver. On smaller units it is normally found "Tee'd" into the compressors discharge line as it enters the receiver. The "safety-valve" is "factory-set" to open and release air into the atmosphere when the pressure in the receiver reaches, or exceeds, the maximum safe limit of that receiver. This valve is a "back-up" to the cut-out or the unloading-control mechanism, and will only operate if, for some reason, the cut-out fails or the compressor does not unload. It is a "legal requirement" that all receivers are fitted with safety valves. It is an "offense" for an unqualified person to interfere, or tamper with this valve in any way.

4.3. Compressed air leaves the receiver through a "main shut-off valve" (also called the "supply-valve"). This valve enables an operator or a maintenance person to shut-off (isolate) the supply to the "Air-Main" when the need arises. (Including an emergency situation).

4.4. If it is necessary to "drain the tank" quickly, then a "drain-valve" is used. The drain-valve, also called the "condensate-valve", is situated at the lowest point of receiver.

There are further "controls" depending on the system design. For example at each "connector point" along a main supply line there should be a "shut-off valve". The purpose of a "shut-off valve" is for the "isolation" of a working unit, without interrupting the supply to other units sharing the supply line. Sometimes this valve is known as an "isolation valve".

NOW VIEW PART 1 OF THE VIDEO.



CAS-1: SELF-TEST EXERCISE NO. 1 COMPRESSED AIR SYSTEMS - OVERVIEW

INSTRUCTIONS

o Answer the following questions without reference to the resource notes or the video.

QUESTIONS (Tick the correct answer/s) YES NO

1. The two compressor types that this module deals with are: a) Rotary and turbine compressors. b) Revolving and rotating compressors. c) Reciprocating and Rotary compressors.

2. Another name for an air-receiver is: a) An air bottle. b) Air tank. c) Air container.

3. The purpose of a "pressure-gauge" in a system is to: a) Measure the air in the tank. b) Check the flow of air. c) Monitor the air-pressure in a system.

4. A compressor will not "over compress" because: a) A cut-out or an unloading device will prevent this. b) The tank will become full. c) The pistons will stop working.

5. All air-receivers must have what, by law? a) A regulator valve. b) A safety valve. c) A water valve.

6. When must a safety valve be adjusted? a) Daily. b) Weekly. c) Never.


7. An air tank can be drained of air and water by the: a) Condensate valve. b) Safety valve. c) Delivery valve.

8. Another term for a "shut-off valve" is: a) A line valve. b) A ball valve. c) An isolation valve.


CAS-1: PART 2 SAFETY WITH COMPRESSED AIR

OVERVIEW Owing to the nature of compressed air, and the pressures associated with it, (Sometimes in excess of 10 bars!) we must be aware of the hazards involved with compressed air systems and working units. The working devices of compressed air systems tend to operate with "sudden action". There is rarely a "progressive or gentle movement" (except perhaps in robotic operations). Further to this we can't see compressed air and even when we sometimes get a blast of air on our skin, it isn't wet or hot, it doesn't give a shock and it "feels" safe. There have been some nasty accidents, involving compressed air and air driven working units, because workers sometimes become lulled into thinking that air can't harm them. Compressed air is far from "harmless", but with some care, and the observation of some basic safety rules, you will not be injured. 1. THE "SHOP AIR-HOSE"

We begin with this because this is probably where the highest cause of "air related" accidents happens. Flexible "Air-hoses" are very commonly used in mechanical workshops, most usually for purposes of cleaning things, and for powering "air tools". A special nozzle, known as an "air gun", is often used to direct a jet of air onto objects in order to blow away dust and debris. Another device commonly used is the "spray gun", so called because liquid can be blown out of the nozzle along with the air. If properly used these two devices can be very useful, but like other things they are often "misused".

The following safety aspects should be noted when using any such device:

o Always wear eye-protection, as debris from the air blast tends to fly back into the face, especially when blowing air into threaded holes.

o Do not direct the air jet at persons around you. Never play the fool in this way, serious injury can result from this foolish behaviour.

o Always direct the air jet away from your body. Never blow air onto your clothing as this can result in dirt and germs penetrating your skin.

o NEVER fill a liquid canister of a liquid cleaning-spray with a flammable liquid such as petrol. The mist can create a highly explosive atmosphere especially if inside a closed area.

o Never fill the canister with toxic liquids either. The resultant "mist" can drift in the air resulting in the possible poisoning of all those in the building, including yourself!

o Never blow metal shavings or filings away from your work area. This dangerous practice can cause serious eye and body injury, including blood poisoning. Use a broom or brush to sweep away metal filings.


The use of air guns and sprays should as far as possible be restricted to exterior areas, such as the wash bay. Always be considerate of others working around you.

It is a fact that some people never seem to learn and for these people the airline is a common instrument used for "horse-play". It is a criminal offence to deliberately aim an airline nozzle or spray at another person. The loss of an eye, or the rupture of an internal body organ, is a painful and sometimes fatal occurrence. NEVER play with compressed air; you will be taking a huge risk if you do!

2. COUPLINGS

Here is an area that causes a great many accidents, primarily because workers just don't bother to apply few "common sense rules".

A lot of working units can simply be "plugged in" or coupled into an air supply line, almost as readily as plugging into an electric wall socket. 2.1. QUICK COUPLINGS

The use of "Quick-Couplers" has become common, especially with "shop tools". The problem with "quick-couplers" is that, when connecting, there can be a sudden rush of air-pressure and force into the line, and into the working-device at the end of that line. For the majority of "small jobs" this presents little problem but potentially it is dangerous.

The correct way to connect any line into the "shop supply" is to:

o Shut off the isolation-valve to that connecting point. o Couple the working line into the coupling (plug in). o Connect the other end to the working unit. o Open the isolation-valve slowly once the connection is firmly in place

(coupled). When uncoupling the correct procedure is to:

o Close the isolation-valve. o Release the pressure in the line, (de-pressurise) by operating the working unit

until it "runs out of air", or releasing the air via a filter drain-cock. o Release (disconnect) the coupling from the take-off point.

2.2. HALF COUPLINGS

Certain "industrial" applications involve the use of "Half Couplings", notably "mobile compressors". Half-couplings simply "twist" together and are held firm by the "locking action" of the mating collars. In many countries, and many industries, it is a "mandatory requirement" that a "safety link" be fitted over half-couplings in order to


prevent the hose from flying off and striking someone in the event that the coupling becomes accidentally "uncoupled" whilst the line is under pressure.

3. WORKING ON AIR POWERED UNITS (MACHINERY)

The most usual accidents involving machinery is associated with the "sudden and unexpected operation" of a unit.

When working on machinery that incorporates such devices as "air-cylinders" or "rams", there is always the chance that a ram will "suddenly" extend, or retract when an airline is being coupled or uncoupled. Again we must always "isolate" the working unit from the air-supply before attempting to couple up, or when disconnecting. The air pressure must be "exhausted" from the line (if uncoupling) before you disconnect any of the supply lines. This can normally be accomplished by closing the main air supply to the machine and then operating the controls until the unit "runs out of air".

Be wary of "spring loaded" components!

Many "single-acting" rams are "spring activated", meaning that they are caused to return to their normal, or "rest" position by a heavy coil-spring. This means that as soon as air pressure is released, (for example when a coupling is disconnected), the piston rod will shoot back (or forward) under "spring-pressure".

4. GENERAL SAFETY TIPS (RULES) 4.1. Electrical Isolation. - Those systems that operate electrically (such as portable units)

should be disconnected from the socket before you begin to work on the unit. Large units will usually require isolation by way of their "mains switch". This must be switched off and locked-out, according to your companies "lock out" requirements/regulations.

! Remember that a compressor can start up at any time if it has not been electrically "isolated"! 4.2. Unload the line. - Wherever possible, the system should be "unloaded" before you disconnect lines. 4.3. Replace any guards. - Such as the "safety guard" that covers a belt, after you have worked on the unit and before starting the compressor. 5. PERSONAL SAFETY 5.1. Always wear safety goggles whenever you use air for cleaning purposes or whenever you are attending to lines or couplings. A sudden release of pressure or "back-spray" can easily project particles of dirt, dust or metal into your face / eyes. 5.2. When using compressed air for cleaning or "blowing off' machinery or components,


always direct the air-stream away from your body. Never allow the air-stream to blow against your skin. This can result in particles penetrating the skin and entering the blood-stream, causing blood poisoning.

5.3. Never point the nozzle of an air-gun toward anyone, and NEVER fool with air. Too many injuries, and even some Deaths, have been the results of "horse-play". It is extremely dangerous to insert an airline nozzle or hose into a "body orifice", not to mention that this is a punishable offence!

5.4. Don't allow flexible lines to lie about on the ground, or upon a dirty surface. Keep the airline neatly rolled up when not in use. Dirt in the nozzle of an air gun will shoot out at high speed and could strike you or a colleague when it is next used. 5.5. NEVER "spin" bearings. This dangerous form of "horse-play" has been the cause of some nasty injuries. An "anti-friction bearing" (caged ball or roller) will

develop tremendous "kinetic energy" as it spins. The trouble is that if there is no lubrication, (as would be the case after a bearing has been washed) then sooner or later the rolling elements are going to "seize". As they do, the outer race-way will suddenly lock up and literally twist off the fingers of the person holding the thing! Further, if the spinning bearing is "let loose" it will whizz off at high speed and slam into anything in its path.

6. GOOD HOUSEKEEPING 6.1. Flexible airlines should be kept neatly rolled when not in use. Retractable pipe drums can help keep airlines in good order and neatly stored. (Garage drive- ways). 6.2. Keep the "compressor room" uncluttered. Access to the compressor unit must never be restricted. Remove any rubbish or objects that could cause a trip or fall whilst trying to get to the unit in emergency. 6.3. Keep protective guards in good condition and secure on the unit. Do not allow debris (rubbish) to collect on or around the guards as this can result in the fouling of air intakes and worse, jamming the drive. 6.4. Wipe up any liquid spills so that you do not cause slipping hazards. This applies to

the draining of "condensate" from the receiver. Where applicable, drain the condensate into a container. (some systems provide a drain line to a nearby drain)

6.5. Keep flexible hoses clean and dry. Do not permit rubber hoses to become coated with oil or fuel (Dieseline etc.) Hoses deteriorate rapidly under these conditions. 6.6. Inspect flexible hoses frequently for signs of damage, perishing or other defects.

Replace those hoses that are in poor condition with new sections of proper quality "air-line".

6.7. Keep the compressor and all related components as clean as possible. Remember that a clean area is most usually a "safe area" too!

NOW VIEW PART 2 OF THE VIDEO.



CAS-1: SELF-TEST EXERCISE NO. 2 COMPRESSED AIR SYSTEMS - SAFETY

INSTRUCTIONS



1. The first safety rule for using an air gun is: a) Wear your hard hat. b) Wear your safety goggles. c) Wear your hearing protectors.

2. The next rule is that when using the air gun you should: a) Always aim the nozzle away from your body. b) Always keep the nozzle pointing downward. c) Always point the nozzle at someone else.

3. Blowing yourself down with the air gun is considered: a) OK as long as the pressure is set low. b) OK as long as you don't get it in your face. c) Not OK as it is dangerous.

4. When using an air gun, it is a punishable offence to: a) Aim the air gun toward a window. b) Aim the nozzle at a fellow worker. c) Stick the nozzle into water.

5. Heavy duty couplings must have: a) A padlock fitted when connecting. b) A safety link fitted when connecting. c) A piece of rag wrapped around it when connecting.

6. Air hoses, when not in use, should be: a) Kept coiled up and stored on a hook or a shelf. b) Coiled neatly upon the ground in a corner. c) Wrapped around something.


7. Air hoses can be damaged by: a) Water. b) Oil and fuel. c) The sun.

8. Compressors with belt drives must be fitted with: a) A sturdy guard over the belts and pulleys. b) A warning notice near the rotating parts. c) A door lock on the compressor room door.

9. Keeping a compressor area free of paper and plastic packets etc. will: a) Prevent fire in the compressor room. b) Prevent air-flow blockages. c) Make the area look better.

10. The main reason we should keep the compressor area tidy is: a) To make the place safer. b) To reduce pollution. c) To make the engineers happy.

THIS CONCLUDES MODULE 1.

When you have finished, have your Supervisor check your work.

In module 2 you will learn the operating principles and maintenance procedures for "Reciprocating Compressors".


MODULE 2 OPERATING PRINCIPLES AND BASIC MAINTENANCE

PART 1 - OPERATING PRINCIPLES BASIC OPERATING PRINCIPLES OF RECIPROCATING TYPE COMPRESSORS A reciprocating compressor, also known as a "piston type" compressor, is the simplest yet possibly the most "efficient" of compressor types. The operating principles are very similar to a simple "bicycle pump" in that a moving plunger called a "piston" in a compressor, moves up and down within a "closed cylinder". Air, drawn in from the "atmosphere", is compressed within the cylinder and then discharged into the "system".

The "Piston" moving up and down (reciprocating) within a closed cylinder draws in a volume of air on its "down-stroke" and then "compresses" that air when it moves back up in the cylinder (the up-stroke). The piston is forced to move up and down, inside the cylinder, by the "crankshaft. A "connecting-rod' joins the piston to the crankshaft. The crankshaft is rotated via a motor, normally an electric motor, but petrol and diesel engines may also be used to "power" the compressor. The motor may be coupled to the compressor via "pulleys and belts".


Belt / Pulley Driven

Sometimes the motor may be "Directly Coupled", also "flanged" to the compressing unit.

Directly Coupled

At the top of the compressors' cylinder is the "cylinder-head". Within, or just below the cylinder-head are "valves" namely:

o An inlet valve-also known as the "suction valve", or intake valve. o An outlet valve -also known as a discharge or delivery valve.

These valves are often contained in a single component part called the "valve-assembly".

Typical valve assembly


THE COMPRESSION CYCLE (single stage operation) Air from the atmosphere enters the space above the piston via the intake valve when the piston descends. The "displacement" of air above the piston as it descends causes a "partial vacuum" in the cylinder. Owing to this vacuum the outside air (atmosphere), being at a higher "pressure" than inside the cylinder, will move into the space above the piston. The intake valve in this condition is forced open by "atmospheric pressure". When the piston begins its "up-stroke" (as forced by the crankshaft) the pressure of the air above it begins to rise and forces the inlet valve to close. This effectively "traps" the air between the top of the piston and the cylinder head. The trapped air is now being "compressed" and the pressure rises rapidly. At a point during the pistons' "up-stroke" the increased pressure causes the "discharge-valve" to open and "compressed air" is discharged out of the cylinder. The discharged air in a "single stage" system will be passed directly into the user-system, or (more commonly) to a receiver. The compressor details so far detailed describe the action going on within a single cylinder of any "reciprocating unit". When a compressor delivers the "final pressure" in "one cylinder" it is known as a "single stage compressor". Some compressors, called "two stage" types, compress in "two stages" (as the name suggests!). The first stage of compression is made as described earlier. However the air discharged from the cylinder (low pressure cylinder) is directed, via an "inter-cooler" (a special tube) into a second, but smaller, cylinder (high-pressure cylinder). The air entering the "2nd stage cylinder" is compressed further to the desired operating pressure (high pressure). A typical 2-stage compressor, showing the internal detail is illustrated below.


TERMINOLOGY It is necessary to know the names of parts, so let’s use the diagram and name those parts.

1. Cylinders. – the model shown has two cylinders namely a Low-Pressure Cylinder and the High-Pressure Cylinder. Note the "cooling fins" that surround both of these.

2. Pistons. - Pistons are sealed between the cylinder walls using "piston rings". The piston rings prevent the escape of pressure past them.

3. Connecting rods. - These "connect" the pistons to the crankshaft. The connecting rods force the pistons up and down within the cylinders as the crankshaft rotates.

4. Crankshaft. - This specially shaped shaft rotates to cause the "reciprocating action" of the pistons. The connecting rod is joined to the crankshaft by a "big-end bearing". The crankshaft is rotated by the "drive-motor".

5. Crankcase. - This is the main "housing" that supports the crankshaft and the cylinders. The crankcase also serves to contain the oil that is necessary to lubricate all the "moving parts".

6. Cylinder heads. - A cylinder head acts to "seal off' the space within the cylinder. Compression of air takes place between the cylinder head and the "crown" of a piston. The suction and the discharge valves are housed within the cylinder heads "ports".

7. Valves. - The valves (or valve assembly) consist of a "suction-valve" and a "discharge-valve". The most common type of valve is known as a "finger-valve". The fingers open and close the holes in the valve-plate depending on which 'stroke" the piston is on. Inlet fingers open due to atmospheric pressure acting on them when the piston moves down in the cylinder. The discharge fingers open when the piston moves up in the cylinder allowing the compressed air to exit. All the fingers are made of strong "spring steel" that serves to keep them closed tightly upon the valve-plate.

8. Inter-stage cooler. - Air leaving the Low-pressure cylinder needs to be cooled before it enters the High-pressure cylinder. As the air passes through the "inter-stage cooler" it transfers heat, caused by the first stage of compression, into the fins surrounding the inter-cooler. The heat is then carried away by the air-stream blowing across the tube. On belt driven units the crankshaft pulley also acts as a "blower fan" to direct a constant air-flow over the cylinders and the cooling tubes whist the compressor is running.


9. Oil level and filler plug. - The model illustrated uses a combination "level check and filler plug". Through this plug we can see the level of the oil and, if required, we can top up the oil through the same opening. Some models use a "sight-glass" for checking oil levels. Other types may provide a "dipstick" type oil level indicator.

10. Safety Valve. - With 2 stage-compressors there is a need to control the discharge pressure from the Low-Pressure cylinder. A safety valve, normally situated at the cylinder head side of the discharge line (inter-stage cooler tube), prevents an excess of pressure from building up. A further safety valve is fitted to the receiver, and if the compressor is "tank-mounted" you will find this (most usually) at the receiver end of the compressors discharge line.

11. Air Filter. - This most vital component serves to protect the compressor and all other "downstream" components from the ravages of dust and dirt. The air filter "traps" dirt and dust, and to a small degree moisture as well, so that the air entering a cylinder is as "pure" as possible. Compressors that operate in dusty areas require larger air filters than those that operate in "clean environments".

TANK MOUNTED UNITS Apart from really large "Industrial" reciprocating compressors you will usually encounter "tank-mounted" units. Illustrated in the following diagram is a typical such unit. We shall learn the part names and the terminology associated with this unit.

The following features are those you must know: o Receiver and base-plate. o Cut-out control. o Safety valve, also called a "relief-valve". o Shut off valve also called the "main-supply valve". o Pressure gauge. o Drain valve, also called the "condensate-valve".

NOW VIEW THE VIDEO SECTION.



CAS-2: SELF-TEST EXERCISE NO. 1 RECIPROCATING COMPRESSORS

INSTRUCTIONS



1. A Compressor that completes final compression in one stroke of a piston is known as: a) A single-phase compressor. b) A single-stage compressor. c) A single-stroke compressor. d) A single-acting compressor.

2. A compressor that has cylinders of two different diameters is known as: a) A twin-cylinder compressor. b) A double-acting compressor. c) A Two-stage compressor. d) A high-pressure compressor.

3. The heavy metal fins that surround a cylinder are designed to: a) Assist with the air-flow. b) Trap dust and dirt. c) Aid in heat dissipation. d) Improve the appearance of the unit.

4. The main purpose of an "Air Filter" is to: a) Prevent water entering the cylinders. b) Prevent air from entering the cylinders. c) Prevent dirt from entering the cylinders. d) Prevent pressure escaping.

5. A safety-valve is needed for the purpose of: a) Preventing overheating in the cylinders. b) Preventing excess "back-pressure". c) Preventing excessive system pressure. d) Preventing excessive heat in the cylinders.


6. The 3 main "moving parts" in a reciprocating compressor are: a) Pistons, condensing-rods and oval-shaft. b) Pistons, connecting-rods and crankshafts. c) Pistons, cam-shaft and crank. d) Pistons, crank-case and head.

7. Water in the air-system is known as: a) Condensed air. b) Condensate. c) Condensed droplets. d) Condensed gas.

8. Water is drained from a receiver by cracking open the: a) Condensate valve. b) Air-main valve. c) Safety valve. d) Inter-stage valve.

9. A compressor will stop automatically when: a) Receiver has too much pressure. b) Receiver is full of water. c) Receiver pressure is at "cut-out" pressure. d) Receiver pressure is above cut-in pressure.

10. A Tank-mounted unit means that: a) The compressor is mounted under the receiver. b) The compressor is mounted off the receiver. c) The compressor is mounted upon the receiver. d) The compressor is mounted inside the receiver.

Check your answers by referring to your notes, the video or asking your Supervisor /

Facilitator.

PROCEED TO PART 2 WHEN YOU HAVE COMPLETED THIS SECTION.


PART 2 MAINTENANCE TASKS

INTRODUCTION Maintenance is performed on compressors at regular intervals in order to keep a unit in good working order. Typically a compressor is given attention at the following intervals:

o Daily or after 8 hours of operation. o Weekly or after 50 hours of operation. o Monthly or after 200 hours of operation. o 3 Monthly or after 500 hours of operation. o Yearly or after 1500 hours of operation.

The attention that must be given at each "Service Interval" is specified in the Operators Instruction Manual for the particular unit. Certain "tasks" must be carried out at each service interval and in this section we are going to explain how to perform those tasks. It must be remembered that the tasks we will describe need only be performed at the "specified interval", but you will be expected to "know" what to do and how to do it when the time comes. STARTING AND STOPPING A COMPRESSOR During routine maintenance you will be required to start up and stop (shut down) a compressor for various reasons. There are some basic rules about how this should be done. STARTING PROCEDURE

o Set the stop / start knob on the cut-out control box to the OFF position. This is usually done by pushing the knob in or down.

o Connect the main supply (i.e. Turn the main switch to the ON position.) o Pull up the stop / start knob (i.e. to the run / operate position).

STOPPING (shut down procedure)

o Always shut down at the cut-out control box stop / start knob. o Do not stop the compressor at the mains-switch, unless it is an EMERGENCY. If you

do stop the compressor at the mains-switch then you will run the risk of overloading the motor when you start up again.

ISOLATING A COMPRESSOR Unless a compressor is "isolated" from its "power supply" there is a chance that it could start up unexpectedly whilst you are working on it. To prevent this happening you must remove the source of power.


With small units the power supply is usually from a "wall socket". In such a case simply remove the plug from the socket and isolation is complete. Larger units may be similarly connected into a 3 phase supply. Again it is a simple matter of switching off and uncoupling the connector. Other units may be hard coupled through a "distribution board". In this case the circuit switches must be switched out and "tagged" so that no-one will reconnect the circuit. BASIC PROCEDURES FOR MAINTENANCE TASKS 1. OIL -LUBRICATION 1.1. OIL LEVEL CHECKS

This is one of the most important checks as a lack of oil can very quickly destroy the compressor. There are 3 types of oil-level checking devices namely:

o Sight glass. o Level plug. o Dipstick.

It is important that the oil level is checked only when the unit is stopped and has been at rest for a few minutes. This delay allows time for the oil to settle in the crankcase.

SIGHT-GLASS

To check the oil level with the sight-glass -observe the glass, wiping it clean if necessary, and check the "level" of the oil against the indicated mark on or next to the glass. The oil should be "visible" in the glass window but not above or below the indicated line.

LEVEL PLUG To check the oil level with a "level-plug" -clean the level plug and surrounding area to prevent dirt dropping inside. Using a correctly fitting spanner, loosen and remove the plug. Observe the oil inside the plug-hole. The oil level is correct if the oil reaches the top of the threaded section, or just runs out of the hole. It is "under filled" if the


oil is at the bottom of the plug-hole or if you cannot see any oil. The unit is "overfilled" if the oil gushes out when the plug is removed.

DIP-STICK

To check the oil where a "dipstick" is used -clean the area around the dipstick to prevent dirt from falling into the tube. Remove the dipstick and wipe it dry with a non-fluffy cloth or paper towel. Insert the dipstick into the tube, making sure that it is pushed fully in. remove the stick and , keeping it in an upright position, observe the oil level against the markings on the stick. The correct level is when the oil aligns with the "full" mark. Oil is LOW if the level is below the mark, and HIGH if above the mark. If there is no oil on the stick then the level is "dangerously low".

1.2. CONDITION OF OIL

Oil does not last forever and sooner or later will need "changing". Between normal "change periods" the oil can be affected by problems such as "overheating" and from "water contamination" (To mention just 2 possibilities). Oils used for compressors are made by many different oil manufacturers and may appear as different colours ranging through light-brown, yellow, orange, green etc. New or "fresh oil" is easy to notice simply because it will appear "clear". Old oil tends to become "darker in colour" and less "clear". When oil becomes very dark, or appears milky, then this is a clue that something is not right.

Black Oil is a sign that the compressor may be operating too hot. A distinctive smell will usually accompany oil that has been "over-heated".

Milky Oil is a sign that water has entered into the oil. Milky oil can also be a sign that the compressor has been operating too cool or for very short periods of time and not reaching an "optimum operating temperature". When this occurs, water from the atmosphere tends to condense in the crankcase whilst the compressor is not operating. If the compressor happens to be a "water cooled" unit then "milky oil" is also a sign that a seal or gasket has "blown", most commonly at the cylinder head joint. If the oil appears the "wrong colour", looks very dark, or milky, or smells unusual, then report this to your Supervisor.

1.3. CHANGING THE OIL All compressors will require an "oil change" at some point in time. The "frequency" of oil changing will depend on many factors, such as:

o Number of hours operated. o Dirt and dust factors in the surrounding air. o Ambient temperatures.

Perhaps the most important factor concerning an oil change (including the topping up of oil) is the "type of oil" used. Compressor manufacturers will


"specify" the grade and the type of oil that must be used in any of their units. It is VERY important that you use ONLY those "specified".

Oil changing involves allowing the old oil to be drained into a suitable container so that it can be correctly disposed of. Do not tip used oil into rivers, streams, the ground or anywhere that will result in "pollution". Used oil should be collected and stored in a special container so that it can be collected by an "oil recycling" company.

Here are some tips that should be followed when you perform an oil change:

o Make sure that the compressor is at "operating temperature", and then "isolate it" before draining the oil. In this way you will ensure that all the "suspended impurities" drain off with the oil.

o Clean and inspect the drain-plug before refitting it. If the plug has a sealing washer (gasket) make sure it is in good condition.

o Refit and tighten the drain plug securely using a correctly fitting spanner. o Always clean around the "filler-neck" area before you open the filler. This is

to reduce the risk of dirt dropping in as you remove the cap. o Make sure that you collect the correct type and grade of oil to fill the unit. o Keep all the containers, funnels, jugs etc. absolutely clean and free of

contamination (such as water). o Pour oil slowly to avoid air locks from blowing the oil back and wasting it. o Fill only to the full mark. o Replace all container lids or caps as soon as the level is correct. This is to

reduce the risk of contamination. o Wipe up any spillage as soon as possible.

2. DRAINING THE "CONDENSATE"

It is perfectly "normal" for condensation to form in a compressed air system; however it is not a good plan to allow it to build up. Condensation is the result of "water vapour" forming into water droplets when the air "cools" after it has been compressed. On "tank mounted" compressor the majority of water collects in the receiver and it is for this reason that a "condensate-drain valve" is fitted to the bottom of a receiver.

On a hot humid day there will be much more water vapour in the air than on a cool day.

You may have to drain the condensate more than once a day when the outside air is hot and humid.

By opening the drain valve just a little, whilst there is still some pressure in the tank, you will quickly see if there is a collection of "condensate" (when you see water spilling out). Open the valve just a little and allow the air to push out all the water. Close the valve when there is only air coming out. Failure to drain the condensate


regularly will cause an excess of water to flow into the main air supply line and cause problems all the way throughout the system.

3. AIR FILTERS

Air filters are a vital part of the total "air treatment in any compressed air system. The purpose of an air filter is to help stop "contaminated air" from entering the compressor and getting into the air supply line. There are many types and makes of air-filters but by far the most "usual" is the "dry-element" type. This type consists mainly of an "element" made of a special "filter medium".Filter mediums are often made from specially prepared paper or other "fibres" that permit the flow of air through them.

A filter medium serves to trap small dust and grit particles within the "pores" or tiny passages that can only be seen through very high magnification. The filter medium is usually contained, and kept in shape with a metal or plastic "frame". Such a configuration is called an "element". Air filter elements are most usually made to be "thrown-away" at certain intervals, although they can be cleaned from time to time in between normal "change periods". Some elements are contained within a metal or a plastic housing that in turn is attached to the "suction port" or "intake" of the compressors' cylinder head. It is common that you will find a separate air filter attached to each "low pressure cylinder" of a "multi-cylinder" 2 stage compressor, and to every cylinder on a single stage "multi-cylinder unit".

Eventually, through use, an element will not be able to trap any further particles of dirt (and dust) and the filter medium effectively becomes "clogged". When the element becomes clogged there is a large drop in the "volume" of air that enters the cylinder and a decrease in the capacity of compressed air delivered to the system. Some types of filters are fitted with an indicator that warns an Operator when the filter is clogged. When the indicator "flags" a warning then it is time to "service" the filter.


3.1. FILTER SERVICING Air filters should be inspected, cleaned or replaced at regular intervals. These "intervals" will be more frequent if the surroundings of the compressor are dusty. Let us overview the standard procedure for "cleaning" a typical "paper element type filter".

o Clean (dust off) the outer case. o Open up the canister cover or lid and remove the element. o Tap the element gently by hand to dislodge heavy dirt / dust. (Do NOT "bash"

the element against a solid object as this will distort the frame and damage the filter medium).

o Blow the element from the inside (not the other way) with an airline. Set pressure to a maximum of 3 bar (45 psi).

o When no further dust emerges then inspect the element by shining a light inside. No "light spots" should be visible through the filter.

o Clean or wipe the filter housing with a damp cloth to remove dust from around the intake area.

o Check the condition of the gaskets or seal and replace if damaged. o Replace the element and secure the cap/cover with the retaining nut / clamp.

Certain types of filter elements may be washed, however, do not wash an element unless the manufacturer recommends or approves this. Washing, using a "non-foaming detergent", may restore an element that is oily, or soot blackened.

The usual washing procedure is as follows:

o Soak the element for about 15 minutes in the recommended solution of detergent / water. Warm water may be used, but never boiling.

o Agitate the element to assist in dislodging the dirt. o After soaking, hose the element down with fresh water to remove all traces

of detergent and residues. o Allow the element to dry naturally, that is, without applying heat.

The following points need to be noted when servicing air filters:

o Never attempt to clean the filter by hitting it against a solid object. This will damage / distort the casing and may rupture the filter medium.

o Never use high pressure from the air-gun as this will rupture the filter medium. Always keep the pressure to a maximum of 3 bar (40 psi).

o "Washable filters" can only be washed a fixed number of times, usually 5 times, and then they must be discarded.

o Discard any filter that is physically damaged or if you can see Pin-holes" of light through the filter medium.

o Remember that an element that is not 100% can seriously damage the compressor and contaminate the whole system.


3.2. ASSEMBLING AND RE-FITTING AN AIR FILTER

There are some very important points that you must always keep in mind when you replace a filter (refit onto the compressor) namely:

o Always check for washers and gaskets. If you happen to "forget" to replace any washer or gasket during re-assembly then you might as well not even bother to fit an air filter at all! The "suction" effect via a bad sealing surface is very strong and dirt definitely will "bypass the filter" and end up in the cylinders!

o The retaining nut of most air filter housing covers normally has a special "sealing washer" beneath it. Always replace this washer for the same reason as described above.

4. DRIVE BELTS N.B.: This section is applicable to units that employ "drive-belts and pulleys".

All belt-driven units must have the drive-belts checked frequently. Loose or damaged belts can result in serious downtime. For a full and complete overview of belts and belt maintenance you can refer to Tech AV programmes BCD (Belt and Chain drives).

The following points need be noted here:

o Always make sure that the compressor is totally ISOLATED before attending to the belts in any way.

o Where necessary, remove the safety-guards. o Inspect the belts visually for damage, wear and contamination (such as oil or

chemical soaking). o Check the belt "tension" and adjust. o Check the belt alignment or "pulley alignment" and adjust if necessary. o Replace the safety-guards and secure.

4.1. BELT INSPECTION Drive-belts must be inspected for the following:

o Splitting and cracking. o Perishing. o Oil soaked condition. o "Shiny" and worn contact surfaces. o Proper "tensioning" and alignment.

Belts that are worn, oil soaked, cracked or perished should be replaced with new belts.


4.2. ADJUSTMENT OF BELTS (NOTE: The full procedure for drive-belt maintenance and adjustment is covered in Tech AV modules BCD)

4.3. GUARDS AND COVERS

o Always replace the belt guard before running the unit. o Inspect the guard for damage and repair or replace any damaged

component. o Make sure that all the fasteners are in place and tightened securely.

5. RUNNING CHECKS

Certain "checks" can only be made with the unit operating or when the system is "charged" with air.

A safety valve is a "compulsory device" and must feature on all systems. All air receivers will have a safety valve somewhere, most commonly at the "discharge end" of the tank. Two stage compressors usually have an "extra" safety-valve situated at the discharge side of the Low Pressure cylinder. This valve is known as the "inter-stage safety valve". There is only one "check" for any safety valve and that is to physically operate it to make sure that it "releases air".

To test a "safety-valve" on a receiver, do the following:

o Run the compressor until it reaches its "cut-out" pressure. o Standing to the side, pull the "pull-ring" on the valve. Air should release. o Let go of the pull ring and the valve should close off immediately. o On models that use a "release lever", operate the lever momentarily. Air

should release. o Let go of the lever and the air should shut off immediately.

If the valves do not release air, or do not shut off immediately then the valve is "faulty" or the cut-out pressure is incorrect. Report this situation to your supervisor without delay.

On absolutely no account should you attempt to "repair" a safety valve! To test the "inter-stage" safety valve on a 2 stage compressor do the following:

o With the compressor operating (and with you standing in such a way that you are clear from the fan, pulleys or any other moving part), pull the "release-ring" of the "inter-stage" safety valve.

o Air should release when the pull-ring is activated. Immediately upon releasing the ring, the air should shut off.


5.1. CUT OUTS AND UNLOADERS To test the operation of cut-out and unloaders you will need to keep your eyes on the main pressure gauge.

o With the unit operating, watch the gauge and note at which pressure the cut-out switches off the motor.

o If the unit has an unloader, then note the pressure at which the un loader activates. You will hear this when the "pitch" of the noise level changes and a release of air is heard from the discharge control-valve.

o Check the manufacturer’s data, or ask your Supervisor what the "cut out pressure" should be, and report if the unit is not "within specification".

5.2. AIR LEAKS

Air leaks are the primary cause of "high operating costs". Even the smallest of leaks will "waste power" and cause the compressor to work harder than it should. Air leaks can occur at every joint and every connection throughout a system. As we are concerned primarily with a tank-mounted unit in this particular module we shall limit the search for air-leaks to the compressor and tank.

To check for air-leaks do the following:

o Make sure that the compressor has shut down and that there is pressure in the tank.

o Listen for "obvious leaks" and mark their positions as applicable. o Use a solution of "soapy water" and paint this onto each joint that

attaches to the receiver. If bubbles appear then a leak exists at that joint. Mark the joint for future identification.

5.3. FASTENERS AND MOUNTINGS

Owing to the vibrations set up in reciprocating compressors there is a tendency for fasteners to loosen. It is therefore important that all the major fasteners are checked for security on a regular basis. The following points should be physically checked, using correctly fitting spanners or wrenches:

o The "pump unit" base bolts. o The electric motor base bolts. o The belt-guard mountings. o Pipe and tube connections (although these are not classified as fasteners,

they can be checked as you perform the other fastener checks.) Loose fittings will contribute to air leaks that in turn result in wasted power and general deficiency in air delivery.

6. CLEANING

Although it may seem unimportant, the cleaning of a compressor unit is vital to its operation. Any air-cooled machine relies totally upon an efficient "heat transfer" between the metal parts and the surrounding air. Anything that interferes with this


heat transfer will cause "overheating" and this in turn will result in "premature failure" of a compressor.

2-stage compressors rely upon a "cooling" effect of the air leaving the low- pressure cylinder before it enters the high-pressure cylinder. This cooling is effected as the air passes through the "inter-stage cooler".

Many compressors are sited in such a way that they become covered in dust and dirt from the local environment. This layer of dust/dirt acts like a blanket and can seriously restrict the transfer of heat away from the cylinders.

6.1. AIR DUSTING AND CLEANING (exterior components) The easiest way to clean a dusty compressor is to simply blow off the dust using an "air gun". Proceed as follows:

o Make sure that you are wearing your safety goggles or suitable "eye-protection".

o Blow from "top to bottom" all over the compressor unit, keeping the nozzle directed away from your body.

o Pay attention to the cooling fins, specifically the fins surrounding the "inter-stage cooler".

o If there is a "wet" accumulation, for example an oil leak that has collected dust, then brush or wipe that area to remove the dirt / grime.

o Do not overlook the "drive-motor" (if equipped) as this too is normally "air cooled". Dust off the motor, or wipe as necessary.

Observe the following precautions when cleaning machinery:

o Do not perform a cleaning operation on a running unit. o Isolate the power before working on it. o Never use a water hose for cleaning, specifically if the unit is still "hot"

from operating. Sudden contraction of metal parts can cause "cracking" or "distortion".

o Never use a water-hose upon an electric motor. If the motor is not rated for water spray then you could be electrocuted.

SUMMARY

In this section we have overviewed many typical "servicing" points typical for most "industrial" and smaller sized reciprocating compressors. It must be stated very clearly that, wherever you have access to the "MANUFACTURERS SERVICE MANUALS", then USE THEM! Always follow the manufacturers’ advice on servicing or maintaining a unit and you will never go wrong!

NOW VIEW THE VIDEO SECTIONS FOR THE VISUAL DEMONSTRATIONS ON THE TASKS MENTIONED

IN THE TEXT.




CAS-2: SELF-TEST EXERCISE NO. 2 RECIPROCATING COMPRESSORS – MAINTENANCE TASKS

INSTRUCTIONS



1. When changing compressor oil you must always: a) Check that the new oil is the correct type and grade. b) Check that the new oil is fresh. c) Check that the new oil is the right colour.

2. When draining the old oil the compressor must be: a) Standing upright. b) At operating temperature. c) At room temperature.

3. Old /drained off oil must be: a) Collected for recycling. b) Thrown in a river or drain. c) Saved for emergency use.

4. Water or "condensate" must be drained regularly from a system to: a) Prevent the pipes from rusting. b) Prevent the receiver exploding. c) Prevent damage to working units.

5. A clogged air-filter element will result in: a) Reduced output from the compressor. b) Hot air being produced in the cylinders. c) Too much air pressure.


6. If you see a "clogging indicator" signal / colour then this means that: a) It’s time to clean the fins around the cylinders. b) It’s time to change the oil. c) It’s time to clean / replace the air filter / element.

7. When "blowing out" an air-filter element the air pressure should be: a) Set as low as possible. b) Set as high as possible. c) Set no more than 300 kPa.

8. The air must be blown through an element: a) From inside to outside. b) In both directions. c) From outside to inside.

9. If you refit an element that has holes or tears in it then: a) The compressor will deliver less air. b) The compressor will overheat. c) The compressor will be damaged.

10. lf you do not refit seals and washers on the filter housing as: a) Oil will bypass the filter. b) Dirt will enter the compressor. c) Air will escape.

11. When you attend to the drive-belt(s) on a compressor you should always: a) Remove the safety guard carefully. b) Isolate the power switch. c) Call a Supervisor.

12. lf one belt on a "multiple set" is damaged or stretched then you must: a) Fit an old belt to replace the damaged one. b) Fit a new belt to replace the damaged one. c) Fit a new "matched set" of belts.


13. It is important to keep a compressor clean because: a) It helps to keep it cool. b) It makes it run smoother. c) It makes it look better.

14. It is important to keep the area around a compressor clean and tidy because: a) It helps the compressor run better. b) It makes the area safer. c) It makes the plant engineer’s happy.


Review your work with your Supervisor or Mentor.

In the next module you can learn about the operation and maintenance of Rotary-Screw Compressors.


MODULE 3 ROTARY SCREW COMPRESSORS

PART 1 - OVERVIEW OF ROTARY TYPE COMPRESSORS OPERATING PRINCIPLES Rotary type compressors are generally used where the requirement for air is "volume" and not necessarily high-pressure. Rotary compressors were originally designed to deliver high volumes (Litres per Minute) of air at "moderate pressure", typically around 3 to 5 bar. Modern designs are now capable of producing pressures in excess of 10 bars (150 psi). You will normally find "rotary" type compressors supplying air to "motors" and "rams" (processing operations) that operate at high frequency. (Many strokes per minute) these units require a high "volume" of air and the rotary compressor is better suited to this than a reciprocating unit. There are various designs or types of rotary compressor however the type known as the "wet screw" is possibly the most widely used, and we shall concentrate our discussions around this type. Illustrated below is a typical "inside view" of a "wet screw" compressor. It is called "wet" because the rotating parts, called "rotors", require "lubrication". BASIC OPERATING PRINCIPLES

The compressor rotors (lobes) are caused to rotate within a closed housing (case). The rotors are driven by the "drive motor". The drive motor may be "directly coupled" to the rotor shaft or the rotors may be "belt driven". As the rotors rotate a "negative pressure" (below atmospheric) is created at the inlet end of the housing. Air enters the casing and is drawn to the rotors that trap the air between the


rotor edges and the inner sides of the housing (case). The "spirals" of the rotors, "meshing" with each other, result in the air being forced into an ever -decreasing space, and at the same time, force the air to move along the rotors length. In this way there is a continuous "flow" of air being drawn in, forced into the screws and then discharged. If we compare the way in which a reciprocating compressor has to pump air in "cycles" then perhaps you can see how the rotary screw type delivers air in a smooth "shock free" manner. N.B.: A colour-coded diagram is provided on the next page as a reference for the notes that follow.


REPLACE THIS PAGE WITH COLOUR DIAGRAM.


LUBRICATION Lubrication is vital to the operation of the wet-screw type compressor and for this reason oil has to be delivered to the rotors in generous amounts. The oil performs the "triple role" of:

o Lubricating the rotors as they slide over each other. o Cooling the rotors. o Sealing to help trap the air between the rotors and the case. (The clearances

between rotor and case are extremely small). Oil is supplied from a large "receiver" and is drawn into the compressor casing, along with the incoming air, when the rotors are revolving. At the "discharge end" of the compressor case, compressed air, mixed with oil, flows into the top of the oil tank where the oil is "separated" from the air. For this reason the oil tank is called an "Air / Oil receiver separator".

An Air / Oil separator

As a result of all the compressing, and friction, going on within the compressor housing (energy conversion) there is a large amount of heat being generated which transfers to the oil (at least most of it does!). By the time the oil has returned to the "receiver / separator" it is very hot and must be cooled before it can be returned to the rotors again. An "oil cooler" is therefore necessary to perform the function of removing the "heat" from the oil before it can be "recycled". An oil cooler is a large "radiator" or "heat exchanger" containing many tubes, surrounded by "air-fins". A "cooling fan", driven by the compressor motor, supplies a constant flow of air over the fins and in this way the heat is "transferred" to the atmosphere. Cool oil then flows out of the "oil-cooler" and returns to the compressor housing.


THE AIR SYSTEM The air (compressed) leaving the discharge side of the compressor housing passes through the air / oil separator and then on into an "air-cooler" (also called an "after-cooler"). Air passing through the cooler transfers its heat, (Caused by compression and friction), into "cooling coils" and thence, by forced air draft, into the atmosphere. The air-cooler "coil" is often situated in the same location as the oil-cooler, and, in this way, the same "cooling fan" serves to force air over both. Air leaving the "after-cooler" may pass directly into a receiver or directly into the plant air-main. One of the "disadvantages" of the wet-screw compressor is that there is always an amount of lubricating-oil present in the air leaving the unit. Added to this there will be the usual "condensation factor" as well. When the two mix (water and oil) in the presence of pressure and flow they tend to "homogenise" (combine) resulting in a rather messy "sludge" which must be prevented from entering the air-main. Before entering into the "air-main" compressed air will usually pass through a "cooling-dryer" in the line directly after the compressor. Incorporated in this cooler/dryer will be an "inlet filter / strainer" of a type that causes heavy particles to "coagulate" and settle in a chamber whilst the "air" carries on into the system. (This will be discussed in more detail in module 4 of this series). Although you will see many other "devices" associated with rotary compressors, we need not go into them at this time. Most of the devices are "control mechanisms" that cause such things as "high temperature "cut-out", pressure regulation and unloading controls etc.

NOW VIEW THE VIDEO CAS-3 PART 1.



CAS-3: SELF-TEST EXERCISE NO. 1 ROTARY-SCREW COMPRESSOR – OPERATING PRINCIPLES

INSTRUCTIONS



1. The major "moving parts" of a rotary-screw compressor are called: a) Pistons. b) Rotor. c) Screws.

2. In a "wet screw" compressor lubrication is necessary to: a) Keep the compressor quiet. b) Prevent wear in the moving parts. c) Stop friction in the air-main.

3. Compressed air and oil are separated in the: a) Oil cooler. b) An air / oil separator. c) After-cooler.

4. The fan in a wet-screw compressor is needed to: a) Push air into the air housing. b) Blowout dust from the coolers. c) Push air over the coolers' fins.

5. The two cooling devices in a wet screw compressor are: a) Oil cooler and a water cooler. b) A radiator and oil cooler. c) An after-cooler and oil cooler.

CHECK YOUR ANSWERS AND THEN PROCEED TO PART 2.


PART 2 MAINTENANCE TASKS

INTRODUCTION Maintenance is performed on compressors at regular intervals in order to keep the unit in good working order. Typically a compressor is given attention at the following intervals: o Daily or after 8 hours of operation. o Weekly or after 50 hours of operation. o Monthly or after 200 hours of operation. o 3 Monthly or after 500 hours of operation. o Yearly or after 1500 hours of operation. The attention that must be given at each "Service Interval" is specified in the Operators Instruction Manual for the particular unit. Certain "tasks" must be carried out at each service interval and in this section we are going to explain how to perform those tasks. It must be remembered that the tasks we will describe need only be performed at the "specified interval", but you will be expected to "know" what to do and how to do it when the time comes. 7. OIL 7.1. OIL LEVEL CHECKS

This is one of the most important checks as a lack of oil can very quickly destroy the compressor. The oil is checked at the "air / oil separator" by means of a sight-glass or an "indicator gauge" (depending on the make or model).

o Observe the glass, wiping it clean if necessary, and check the "level" of the oil against the indicated mark on the glass. The oil should be "visible" in the glass window but not below the line.

7.2. TOPPING UP THE OIL NOTE: The main outlet-valve must be closed for the following operations.

o It is important that the air / oil receiver is "de-pressurised' before you can add oil. Typically the filler-plug, must be loosened, or an internal "depressurising valve has to be cracked open". Only when the escaping air can no longer be heard can you fully remove the filler plug.

o Using ONLY the "recommended oil", add sufficient oil to bring the oil level up to the "full" mark. On some makes the oil must completely fill the sight glass. On other models featuring a "gauge-needle type indicator" the level must not exceed the "maximum or high mark".

o Replace the filler cap fully and secure with a correctly fitting spanner. o Record the amount of oil used to "top-up" for purposes of maintenance

planning and data collection.


7.3. CHANGING OIL AND FILTER CARTRIDGE Under usual (Normal) conditions oil should be changed after every 1000 hours of operation. Follow the procedure below as a general guide, but always follow the manufacturer’s instructions where available:

OIL CHANGE

o Run the unit for enough time for it to reach "normal operating temperature". o Switch the control to the "Unload" position and allow the unit to run for at

least 30 seconds, and then shut the unit down. (most units will do this automatically when a "normal shut-down" is made.)

o Close the "air-outlet valve" and then de-pressurise the air / oil receiver in the manner explained in "topping-up procedure".

o Place a suitable "catcher-bowl" or container beneath the drain-hose (plug). o Keeping the drain valve closed, connect a drain hose to the drain line. o Place the drain line into the catcher bowl and then open the drain valve and

allow the old oil to drain out. This will usually take some time for draining to be completed, so during this time proceed to the next task (changing the filter).

o Allow enough time for all the oil to finish draining and then replace the drain plug, securing it firmly.

o Close the drain-valve, disconnect the drain hose and re-plug the drain line. o Fill the "air / oil receiver" with fresh, clean oil of the CORRECT TYPE AND

GRADE, to a level above the "normal mark" but below the "high" mark on an indicator gauge, or to completely fill the sight-glass on other types.

o Replace and secure the filler plug. CHANGING THE OIL FILTER ELEMENT

o Place a catcher tray beneath the filter cartridge. o Unscrew the filter, using a filter wrench if necessary. o Drop the cartridge and oil into the catcher bowl. o Thoroughly clean the filter head. Wipe away all dirt and old oil, specifically in

the area where the "filter-head seal" is seated. o Remove the new filter from its packing, and remove the protective cover (If

fitted). o Holding the filter upright, fill it with clean oil. This is known as "charging the

filter”. o Lightly "oil" the rubber sealing-ring at the top of the element using the same

oil as in the system. (This will help prevent the seal from twisting when fitting).

o Thread the element onto its adapter and tighten by HAND only. (DO NOT OVERTIGHTEN).

N.B.: At this time it is assumed that the air / oil receiver has been filled with oil and we are ready to operate the unit.


o Start the unit and allow it to operate, on load, until normal operating temperature is reached. During this time check for OIL LEAKAGE at the filter elements' joint. Stop the unit if a leak is seen.

o When working temperature has been reached, stop the unit (Unload it first) and allow at least 5 minutes for the oil to settle.

8. AIR (INTAKE) FILTER SERVICE

Dust contained in the incoming air is held (retained) by the filter-medium of the air-intake filter. Depending on local "atmospheric conditions" the filter will need to be "serviced" before the filter medium becomes "clogged" with airborne solids / particles.

Some makes and models of compressors will offer a "clogging-indicator" that warns when an air filter is becoming clogged. An indicator can be a simple "pilot light / illuminator" that lights up on the control panel. Other manufacturers may use a "vacuum gauge" Under "normal conditions" a filter element is renewed after 1500 operating hours have elapsed (or upon the manufacturer’s recommendation). In between this period the filter may require "blowing out".

8.1. BLOWING OUT PROCEDURE

The aim of "blowing out" an element is to force out the dirt and dust particles that are trapped in the "filter medium". All the particles entered the filter from the OUTSIDE and were trapped as they moved INWARD through the filter medium. When we "blow a filter" we must always remember to force those particles back from where they came, not try to push them FURTHER into the filter medium. Blowing an element from the outside to the inside will simply result in the element becoming "further clogged", and may also cause tiny "pinprick holes" to develop as well.

The (typical) procedure to "clean an element" is as follows:

o Make sure that the compressor is shut off and isolated. o Wipe (clean) the outside of the filter housing. o Slacken, and remove the cover screw or nut, then remove the cover. On

some units the whole filter housing will be secured by a single "central fastener", in which case remove the complete unit.

o Remove the "filter element", or separate the element from the housing. o Keep the element in a clean and dry place, in other words don't leave it lying

about in the dirt and dust of the ground around you! o Cover the intake "adaptor" (with cloth or plastic sheet) to prevent dust

entering the compressor through this opening. o If an element is particularly "dusty" then give it a few "taps" with your hands

to dislodge the "heavy dust" that has accumulated on the outer edges. DO NOT "Hammer" the element against solid objects, this will result in damage to the element and could destroy the compressor!


o Connect your "duster / air-gun" to the shop air supply via a regulator. Set the regulator to a maximum of 3 bar (40 psi).

o Blow through the element FROM THE INSIDE to remove the dust. o When no further dust can be seen coming of the element as you apply air

then it can be presumed "clean". 8.2. "LIGHT TESTING" AN ELEMENT

It has to be understood that the filter element on any compressor is a VITAL component. If an element has even a "pinprick sized hole" in it then that element has to be "thrown away" and a NEW element fitted in its place. Just one tiny hole will permit dirt or grit to enter the cylinders and cause severe wear to all the moving parts. When wear occurs, then the "clearance" between the rotor tips and the housing INCREASES and the result, apart from mechanical destruction, is a decrease in the "output" or "volume of air being delivered".

We are telling you all this because it is important that you pay particular attention to the CONDITION of an element, before you simply replace it back into position. It is possible to see whether any "pinprick-holes" exist in an element simply by holding an "inspection lamp" in the centre of the element and looking "though the element" from the outside.

If you can see ANY "bright-light" then the element is DAMAGED and must be DISCARDED.

NOTE: It is far less expensive to fit a new element than to overhaul a compressor! 8.3. REFITTING THE FILTER UNIT All the components of a "filter assembly", inside and out, must be wiped clean before the unit is replaced onto the intake adaptor.

o Pay particular attention to any sealing devices such as "O-rings", gaskets and sealing washers. If any "sealing device" is worn, damaged, perished or in any way "looks suspicious" then fit new parts. DO NOT LEAVE THEM OFF! Seals playa very important role and if you leave them off, (or forget to put them back!), you might as well not even bother fitting the filter; the compressor will be ruined in quick time anyway!

o When mounting the filter housing onto the adaptor neck, make sure that it "seats" properly (squarely). Replace and secure the "securing fastener" (nut or screw) firmly, but don't over tighten as this could result in a cracked or a distorted housing, (especially if a plastic housing is fitted).

9. BELTS AND PULLEYS (where applicable)

On models that utilise belts (between motor and rotor shaft) it will be necessary to inspect these during routine maintenance.


Drive-belts must be inspected for the following: o Splitting and cracking. o Perishing. o Oil soaked condition. o "Shiny" and worn contact surfaces. o Proper "tensioning" and alignment.

Belts that are worn, oil soaked, cracked or perished should be replaced with new belts. (For full details on belt maintenance see Tech AV Module BCD-2). 10. SCREENS AND HEAT EXCHANGERS (Coolers)

Most rotary screw compressors are contained within "cabinets". Outside air is drawn into the cabinet (and thence into the intake) through "air vents" in the cabinet casing. When the compressor is operating there is a powerful "suction" through these vents. If there is any debris (rubbish) lying about in the general area of the compressor then it is very likely to become sucked into these vents and result in a "restriction" to the air-flow. This in turn will result in a reduction of compressor output, and other problems.

Where necessary, and whenever noticed, clear the screen / vents of any debris that has been pulled into them. This will usually involve a DAILY inspection, especially if your compressor is in an area prone to this problem.

At the opposite end of the cabinet there will be "exhaust vents" through which the "forced air" will escape. Forced-air is created by the "cooling fan" that blows air over the "after-cooler" and the "oil-cooler".

The cooling-fins of both the after-cooler and the oil-cooler will require periodic "blowing out" to remove the accumulation of dust and rubbish that usually collects in them. As you did with the air filter, blow the dust in the opposite direction to the forced air-flow. As you "blow" the fins, be on the lookout for oil leaks, especially in the oil cooler area. Oil leaks can result in heavy dirt accumulation between the fins and this will result in overheating of the compressor. Oil leaks also result in excessive oil consumption and risk of mechanical failure in the "air end unit" (I.e. the compressor unit/rotary lobes and the bearings etc.)

Always report to your supervisor if you notice oil leaks.

Having cleared the intake vents and cleaned the cooling fins, take the time to clean the compressor area itself. Pay particular attention to the "drive-motor" as a collection of dirt and dust on this will result in an overheated motor and eventual failure.


To complete the "service", replace all the side and end-panels and Wipe the unit to remove oily hand marks. Operate the compressor, on load, (open the main delivery valve) and keep your eye on things for a few minutes. Check that all is operating correctly and that there are no air or oil leaks.

Clean up the work area and pack away your tools.

In part 2 of the video you will be shown how to perform most of the "basic servicing" tasks that we have just described.

Now view Part 2 of the video. INSTRUCTION

When you have completed viewing the video, and if you think that you now are able to perform the tasks without assistance, then attempt the Self-Test Exercise No. 2 for this module.



CAS-3: SELF TEST EXERCISE NO. 2 ROTARY – SCREW COMPRESSOR MAINTENANCE

INSTRUCTIONS



1. The correct oil "level" is when: a) The sight glass is clean. b) The oil can be seen in the sight glass. c) The oil is in line with the indicated line.

2. Before topping up the oil in the receiver you must: (tick most appropriate) a) De-pressurise the compressor. b) Open the "air-mains". c) Remove the filler cap. d) Clean the filler jug.

3. The type of oil to be used when topping up is: a) SAE 10 or equivalent. b) Motor oil as used in an engine. c) That specified by manufacturer. d) The drum closest to you.

4. Whilst you are waiting for the oil to drain from the air / oil receiver you can: a) Change the oil filter. b) Clean the cooling fins. c) Watch the oil draining. d) Take a tea break.

5. Old oil should be: a) Drained out into a river. b) Flushed down a drain. c) Collected for recycling. d) Sold to second-hand car dealers.


6. An air filter element must be renewed: a) When the compressor becomes noisy. b) When the compressor has a major service. c) When the "clogging Indicator" warns. d) At 10000 hour intervals.

7. If you leave washers and seals off an air filter housing then: a) Dirt will bypass the housing and enter the compressor. b) Oil will leak past the unsealed areas. c) No major problem will be experienced. d) You'll have to put them on at the next service.

8. A distorted air filter housing can result in: a) Too much air getting into the compressor. b) Dirt entering the rotor housing. c) Overheating of the motor. d) Reduction in delivered air pressure.

9. Blowing off the dust and dirt from the cooler-cores will: a) Improve the cooling efficiency of the coolers. b) Improve the output of the fan. c) Keep the unit looking better d) Make the unit run smoothly.

10. The correct method of shutting down a screw type compressor is: a) Switch off the power at the mains. b) Shut off the main supply valve and then wait. c) Switch to the "unload position" and then press the stop

button. d) Hit the emergency stop button.

THIS CONCLUDES MODULE 3 IN THIS SERIES.

Have your supervisor / mentor check your work to complete the module.


MODULE 4 AIR TREATMENT AND SYSTEM MAINTENANCE

PART 1 - AIR TREATMENT OVERVIEW AIR TREATMENT Compressed air most usually contains all kinds of "contaminants" most of which can result in damage to pneumatic devices and the possible "spoiling" of products. Most users of compressed air require some degree of "treatment" to the supplied air in order to reduce the damaging effects of contaminants. The primary contaminants in most systems are water, dirt and oil. All of these contaminants can be controlled by "Air Treatment". There are basically two categories of "air treatment" namely:

1. Primary Air Treatment. 2. Secondary Air Treatment.

PRIMARY AIR TREATMENT The principle units that are classified as being "primary air treatment" devises are:

o Air-intake Filters - That retard and reduce the intake of "airborne contaminants". o After-coolers - That reduce the temperature of air directly after it has been

compressed. o Separators - That trap residues such as water, oil and solid particles. o Dryers - That reduce the "moisture-content" of air before it enters the main loop or

line. Primary air treatment is therefore the part of the system that ensures that clean and dry air enters the "air main".


SECONDARY AIR TREATMENT Even when relatively clean and dry air enters the air-main there is still a large risk of further contamination reaching the working units. This contamination can be generated within the air main itself and the most likely problems would include:

o Rust particles. o Oil vapour. o Scale from the metal surfaces of the piping. o Dirt.

All of these can cause problems in working units and in pneumatic control devices. Secondary air treatment devices normally consist of filters, regulators and lubricators. These units are most usually placed in close proximity to the working unit.

o FILTERS - are designed to trap any contaminants from the air and prevent them from entering the "working unit". Most filters trap both water (condensate) and solid particles. Water and heavy solid particles collect in a bowl, normally transparent, beneath the "filter-head". Smaller solid particles are trapped within a small "particle filter element" normally situated in the top of the filter housing. In an air system there can be two types of filters namely:

o Particulate filters, and o Coalescing filters.

Particulate filters are designed to trap particles (contaminants) such as dust and metal particles and usually work in the 5 micron range. This means that the filter will trap particles that are larger than (or thicker than) 0,005 mm. The particulate filter also acts as a "moisture-trap", as do most airline filters.

Coalescing filters are designed to trap "liquid and vapour", specifically water and Aerosols (the term given to vaporised substances such as oil).


o LUBRICATORS. - These are installed in line that operates "power tools" or "actuators" in order to ensure that "moving parts" receive lubrication. A lubricator is an "automatic device" that delivers a "calibrated" amount of "clean-oil" into the air-stream before the air enters the machine. Oil is only "dispensed" if there is a flow of air through the lubricator.

o PRESSURE-REGULATORS. - The primary purpose of a "regulator" is to set the air pressure in a "working-line" to a "constant value". The regulator is normally fitted on the "down-stream" side of a filter but always before (up-stream) a lubricator.


Sometimes a filter, regulator and a lubricator are supplied as a combined set called an "air service unit".

Service Unit

MAINTENANCE OF AIR TREATMENT DEVICES

As we might expect, there will be some maintenance involved in the upkeep of the devices used to treat the air in a system. Mostly the maintenance involves draining off the "condensate" and cleaning or replacing the filter elements. In the case of lubricators we will also need to replenish oil levels and adjust "flow rates" from time to time. In the next section we shall look at typical maintenance procedures on commonly found devices.

NOW VIEW THE VIDEO FOR THIS SECTION.



CAS-4: SELF-TEST EXERCISE NO. 1 AIR TREATMENT

INSTRUCTIONS


o Place a tick next to the answer that, in your opinion, is most appropriate to the question.


1. The two most likely contaminants to enter a "compressed air system" are: a) Water and paper. b) Oil and gas. c) Dust and water vapour.

2. Primary Air Treatment deals with: a) The removal of contaminants from the atmosphere. b) The removal of contaminants before the air-main. c) The removal of contaminants from the working units.

3. Secondary Air treatment deals with: a) The protection of the working units. b) The protection of the compressor. c) The control of speed of the working unit.

4. The first Primary air treatment device in any system is: a) The compressors' Oil Filter. b) The compressors Air Filter. c) The compressors receiver.

5. Another name for the water that collects in an air system is: a) Condensate. b) Condensed air. c) Condensed water.


6. In order to force moisture to condense, the compressed air must be: a) Heated. b) Cooled. c) Filtered.

7. The purpose of an "After-Cooler" is to: a) Help dry the compressed air. b) Increase the water vapour. c) Heat the atmosphere.

8. The purpose of a Separator / Filter is to: a) Separate air from contaminants. b) Separate water from dirt. c) Separate oil from dust.

9. A Particulate Filter element is used mainly for: a) Trapping solid particles. b) Trapping liquid. c) Trapping vapour.

10. A Coalescing Filter Element is used for: a) Trapping solids particles. b) Trapping vapours. c) Trapping particles larger than ,005 mm.

11. A lubricator provides: a) A steady stream of oil into the compressor. b) A fine mist of oil into a working unit. c) A spray of oil into the air-main.

12. The main purpose of a regulator is: a) To increase the working pressure to a working-unit. b) To maintain a steady pressure at the working-unit. c) To increase the air flow to the working-unit.

CHECK YOUR ANSWERS AND CORRECT ANY MISTAKES BEFORE YOU MOVE ON TO THE NEXT SECTION.


PART 2 SYSTEM MAINTENANCE

Most maintenance tasks on the compressed air system are very simple, yet as simple as they are, it is vital that they be done on a regular basis to avoid costly breakdowns. In this section of the module we are going to explain the "small" but important routine type maintenance tasks that should be made on a regular basis to any air system, small or large. 1. DAILY CHECKS AND TASKS

All drains and moisture traps should be checked on a daily basis. If you live in a country that has a hot and humid climate it may even be necessary to do these checks every few hours! Many devices have "automatic drains" which means that the "condensate" will be drained whenever the water level reaches a certain level in the "collection bowl". It should be noted that automatic drains should be checked from time to time. You will normally find that most filters, moisture traps and separators will have a means of draining their "catcher bowls" manually.

1.1. DRAINING CONDENSATE (WATER) FROM TRAPS AND FILTERS In order to drain off water simply "crack open" the manual drain valve at the bottom of the bowl. As a point of "good-housekeeping" collect the "condensate" in a container rather than simply draining it onto the floor or ground. Condensate will often contain oil and certain chemical compounds as well, more so in the case of "separators". For this reason it you should never drink this liquid! If you drain onto the floor you also run the risk of creating a slipping hazard in your workplace. Do not open the drain valve fully. When pressure is in the system, you only need to "crack open" (slightly open) the drain-cock or valve. Any liquid will generally pour out past the open valve seat quickly. Shut off the valve as soon as it is obvious that there is no more liquid running out. 1.2. FILTER CHECKS

As most filters also have drain cocks then these too must be checked daily and any water drained off. The purpose of a pure "filter" is to trap solids, and in some types, to collect liquids and "vapour". Filters elements will at some stage require either cleaning or in most cases, renewing. It’s time to fit a new filter when:

o The filter has operated for a set number of hours, days or weeks. o The working units seem to be losing speed or power. o The "clogging indicator" signals its' "tell-tale warning".


1.3. CHANGING A FILTER-ELEMENT o Make sure that the air is shut-off to that filter and the line is "bled" of air. o Depending on type and design release the filter-bowl and detach it from the

filter head. o Detach the element from the filter head. Note that the element is generally a

"screw-in" type. o Wash all the parts using water based solvent. Note: certain solvents may

affect Plastic components. Always refer to the filter manufacturers' instruction on cleaning and the use of solvents.

o As a general rule it is UNSAFE to use flammable solvents or fuels to clean any component in the system!

o Inspect the filter element. If the filter is dirty then either replace it with a new element or, if recommended by the manufacturer, wash it in a suitable solvent. Then, as you learnt with "air filter-elements", blow it out with compressed air in a reverse direction to normal airflow.

o Clean the filter head and check that there is no damage in this area. o Obtain a new filter element, or the cleaned filter element. o Where applicable, check that the "rubber or plastic seal" in the element is in

position and in good order. o Carefully screw the element into the filter head and tighten it by hand only. o Wipe dry the filter bowl and replace it into the filter head. Note that the

manner in which a filter bowl attaches to the filter head can vary from make to make. As a general rule make sure that the bowl is "locked" into position, and, where applicable make sure that the outer "retainer bowl" is fitted.

o Introduce air (pressure) into the filter SLOWLY by gently opening the shut-off valve. If you open the valve quickly the sudden rush of pressure could result in the filter becoming unseated, or the bowl could crack especially if it is a plastic unit.

o Check the unit for leaks. 2. MAINTAINING COOLER UNITS

The majority of coolers that you will encounter will be "air-cooled" types that involve "core type heat exchangers" and a fan to blow air over or through them. The biggest problem with air-cooled units is that the heat-exchanger cores tend to become covered in dust and dirt. Another problem is that because there is a very strong "forced draft" created there is the tendency for rubbish and debris to collect (by suction) in intake vents and screens. Both of these problems result in a reduction of the "cooling effect" of the compressed air flowing within the cores. Maintenance therefore involves the daily inspection of the cooling cores for dirt and for blockages of "intake vents".


2.1. CLEANING CORES The most practical way to clean a core is to blow compressed air over the "fins". Blow in the reverse direction to the normal "fan" in order to achieve best results. The basic steps are as follows:

o Make sure that the unit is not operating and that it is isolated at the main power supply. Note that "refrigerated coolers" will have their own power supply so make sure to isolate this.

o Where applicable, remove the covers in order to gain access to the inner workings.

o Blow air, using a suitable "duster gun", across the cooling fins of the heat exchanger cores. Be careful, you don't want to damage the fins. The cooling fins are normally very flimsy and will bend easily if you allow the nozzle of the gun to make contact with them. If you do happen to bend a fin or two then you will have to "straighten" them. Bent fins can result in a loss of cooling. Don't forget to wear your safety goggles as dirt can easily fly back into your face in this task.

o Blow away any accumulated dust etc. from the other components (such as the fan motor) at this time.

o Check the security of line connections where applicable. o Replace the covers securely. o Reconnect the power and check that the unit operates.

3. PRESSURE REGULATORS

There is actually no maintenance necessary on pressure regulators. All that need be done is to check that the pressure is maintained at the desired setting. This is done by observing the pressure-gauge on units that feature a gauge. Some units do not feature a pressure-gauge; instead they have a calibrated collar or ring to mark the setting.

4. LUBRICATORS A lubricator delivers oil to working units that require lubrication. There are two checks that you need to make on a daily basis.

o Oil Level check and replenishment. o Oil "flow" check.

4.1. Oil-level. - Can be checked simply by observing the oil through the transparent bowl

of the lubricator. There should always be a visible amount of oil present. To top up the oil follow this procedure:

o Shut off the air at the isolation valve. o Bleed the air out of the line. o Obtain some oil of the correct type for the lubricator/tool being used. o Clean off any dust or dirt from the top of the lubricator housing. o Slacken and then remove the filler plug in the housing (top).


o Top up the bowl to the indicated level, or to the top of the bowl. o Replace the filler plug and tighten it. o Open the isolation valve "slowly" to prevent a "shock load".

4.2. Oil flow - This check is made whilst the "working unit" is operating.

o Observe the oil drip inside the "bubble-window" in the top of the unit. o Note that the flow rate will vary according to the tool or unit that is

operating. If the working unit is not actually operating there will be no "drip". o If necessary, use a small screwdriver and turn the adjuster screw (situated

next to the filler plug) by a small amount. Turning "in" or "down" usually increases the flow and vice-versa. Set the "drip rate" to the desired amount. For example the oil "demand" for a small impact wrench might be in the region of 2-3 drips per minute. The desired rate for an "air-grinder" might be in the region of 5-6 drips per minute.

o In the case of most air-powered tools, looking at the exhaust vent/port of the air tool can roughly assess the lubrication-rate. A well-lubricated tool will have a "trace" of oil around the vent. An over-lubricated tool will be wet around the vent.

5. AIR LEAKS

Air leaks are not only annoying but they cost the company money too! Don't think that compressed-air is "free". Whenever a compressor starts up, or comes "on load" it uses up power, and Power costs money! Air leaks are not difficult to notice as they tend to make quite a lot of noise. Small leaks tend to give of a high pitched "squeal" but many small leaks can go unnoticed inside a noisy factory. It is the "small leaks" that cause most power wasting as they are often ignored, however, several small leaks in a main or a branch line can result in a lot of wasted power.

The most likely places for leaks to occur are the following:

o All threaded joints. o Filter casings or bowl seals. o Valve packings. o Flexible connection lines (including the shop air-hose).

To check for leaks at any of these positions, simply apply some soapy water to the joint. If bubbles begin to form there is a leak. Begin your check at the compressor delivery and follow the "main" and all the branches. Mark the position of each leak with a suitable permanent marker and continue the check throughout the line. Report all located leaks to your Supervisor.


AIR TOOLS - LUBRICATION Air tools can be badly damaged through contaminants in the air supply. If you are using any air tool such as an "impact-wrench", "air-grinder", "buffing-tool" or "drilling machine" it is not recommended to connect them to an air-line that has not been fitted with a filter and moisture trap.

Ideally the line should have a full "service unit" installed for use with "motorised air tools". When water (condensate) enters the tool it will "flush" away any lubricant in the motor. When the tool is stored away then "rust" will start to form on the moving parts. In this way the moving parts will quickly become worn away and soon the tool will be rendered useless".

If your airline does not have a "lubricator" then the air tool should be lubricated "manually". A few drops of the recommended lubricant should be put into the air intake (line-connector) of the tool. This should be done at least daily before the tool is used.

THIS CONCLUDES MODULE 4 IN THIS SERIES.


CAS-4: SELF-TEST EXERCISE NO. 2 AIR SYSTEM MAINTENANCE

INSTRUCTIONS



1. What "daily" task should be made on any system? a) Drain the receiver. b) Drain the moisture traps. c) Drain the pipes.

2. When draining condensate from a receiver we should: a) Open the drain valve fully. b) Crack the valve open. c) Leave it until all the air has drained out.

3. Before you can dismantle a filter you will have to: a) Isolate and drain the working line. b) Put on your personal protective equipment. c) Switch off the compressor.

4. When you clean a filter bowl, specifically a plastic bowl, you should: a) Use a lot of hot water. b) Check the manufacturers' recommendations. c) Use a strong detergent or solvent.

5. Filter elements in "filter/separators" must be: a) Washed and blown dry. b) Renewed when necessary. c) Cleaned with petrol.

6. An isolation valve must always be opened slowly, to prevent: a) A shock load to the filter unit. b) A blast of air hitting you. c) A working unit from blowing up.


7. After-coolers and dryers do not work efficiently if: a) The weather is too hot or cold. b) They are clogged with dirt. c) The air flow is too fast.

8. The maintenance needed on pressure regulators includes: a) Dismantling and cleaning all the parts. b) Nothing at all. c) Checking that the pressure setting is correct.

9. The maintenance required to lubricators includes: a) Replenishing oil and setting the flow rate. b) Draining off the water daily. c) Wiping it clean.

10. The lubricator is set correctly if: a) Oil is seen dripping from the exhaust vent of an air-tool. b) No oil is seen at the exhaust vent. c) A light coating of oil is seen or felt at the exhaust vent.

11. Air leaks in a system are fixed because: a) They are noisy and annoy the workers. b) They waste power. c) They generate heat.

Have your supervisor check your work to complete this section.


(cas) - techav

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