compree 1

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COMPRESSED AIR PAGE 1


Compressed Air

Supply

Training Notes

Trainee: .. .

Course Date: ..

SJM IssB June99



A. CONTENTS

SECTION SUBJECT PAGE

1. Introduction 3

2. Units of Pressure 3

3. The Compressed Air Circuit 4

4. Air Compressors 5

Displacement 5

Free Air Delivery 5

Air Compressor Types 6

Diaphragm Compressors 6

Piston Compressors 6

Sliding Vane Compressors 7

Helical & Spiral Lobe Compressors (Screw) 7

Care of Compressors 7

5. Compressed Air Dryers 7

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Refrigerated Dryers 7

Desiccant Dryers 8

6. Compressed Air Receiver 8

7. Metal Air Supply Pipework 9

8. Air Management Systems 9

DeVilbiss DVFR Range 11

DeVilbiss DVFR-2 Filter/Regulator/Coalescer Operation 12

Filter Unit 12

Regulator Unit 12

Coalescer Unit 13

Semi-Auto Drains 13

9. Hoses 13

Construction 13

Inner Tube 13

Reinforcement 13

Cover 14

Hose Types 14

DeVilbiss Red Rubber Air Hose 14

DeVilbiss Red Line & Euroline Air Hose 14

Nylon Air & Fluid Hose 14

Polythene Air/Fluid Hose 15

Air Hose Pressure Loss 15

Hose Connections 16

Quick Detachable Connections (Q/D s) 16

Hose Care, Storage & Inspection 17

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10. Equipment Air Consumption 17

Pressure drop in a Conventional Gun Air System 18

Pressure drop in a GTI Gun Air System 19

Sectioned drawing of a DeVilbiss DVFR-2 20



1. Introduction

The process of spraying is most simply defined as a mechanical means of applying

material . Mechanical because either automatic or manual machines (i.e. spray guns) are

providing the method of control when applying the material to its substrate.

In this training session we are concerned solely with the application of material to a given

surface and the tools used to do it. The primary tool we will use is a Spray Gun and the

material to be sprayed is normally Paint.

The minimum amount of equipment required to carry out this depends upon the particular

material being applied. The items will however, normally fall into two groups:

1. Air Compressor 1. Air Compressor

2. Compressed Air Receiver 2. Compressed Air Receiver

3. Filter/Regulator Unit 3. Filter/Regulator Unit

4. Air Hoses 4. Air and Material Hoses

5. Suction/Gravity Feed Material Container 5. Pressure Feed Material Tank

6. The Spray Gun 6. The Spray Gun

Before moving onto the spray equipment (5 & 6), we need to examine the air supply system

and the benefits that can be obtained by choosing and using the correct basic equipment.

2. Units of Pressure

A compressed air system always forms a complete circuit,

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beginning and ending with atmospheric air pressure. This is usually

assumed to be between 14.7 - 15 Pounds per Square Inch (psi) or

approximately 1 Atmosphere. Alternatively this pressure is known

as 1 Bar. Atmospheric air pressure will slightly change depending

upon the weather condition being experienced at a particular time.

Look at the weather forecast on the television - you will see curved

lines joining points of equal atmospheric pressure (called Isobars)

marked on the map - marked in millibar (mbar or 1000 th s of a

Bar). In the British Isles the atmospheric pressure typically varies

from 980 to 1030 mbar. However, because atmospheric pressure is always around us, and it

varies (relatively) only very little, we tend to ignore it, and therefore calibrate our pressure

gauges to read 0 psi at 1 Atm. This is known as Pounds per square inch gauge or psig.

However, just to confuse everybody, we normally just call it psi . With the increasing use of

Metric units, and depending upon where you are in the World several different units may be

used.

14.7 psi = 1 bar = 100 kPa = 1 kg/cm

2

= 750 mm Mercury



3. The Compressed Air Circuit

The air is taken into the compressor and work is done when compressing the air, normally by

a factor of 8:1 or 10:1, depending on the specification and performance of the compressor.

The energy involved in

compressing the air is

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transferred from the power

source, e.g.: electric motor or

internal combustion engine,

to the air in the form of the

pressurisation process. In a

perfect world the transfer of

energy would be 100%, but

in fact it is considerably less.

This is the first point in the

circuit where work is done

and energy is consumed.

The amount of energy used

will depend not only on the

final pressure but also on the

volume of air per minute that the compressor is required to compress.

The compressed air is then fed into the distribution system (hard pipework), where air will

flow until the pressure in the system equals the pressure supplied by the compressor.

For normal applications, this stored air pressure is far too high, so a pressure control device,

called an Air Regulator, is fitted and used. Its purpose is to reduce the input air pressure

supplied (anything up to 200 psi in normal working conditions) to a usable pressure of

between 1 psi to 90 psi at its output and maintain that pressure

constantly. This will only be possible if:

a) the compressor maintains the line pressure above the required

regulator output pressure, and

b) the air regulator is capable of handling the volume of air being

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demanded by the user tool.

The regulator output pressure is transferred via flexible supply

hoses to the tool - the spray gun, sander etc. Air will flow along

the lines until the pressure in them has built up to the regulator

pressure. Again, while the air is flowing, work will be done and

energy will be used up.

It is important to note that onlywhen air is flowing is work being

done, and energy used up. Because the energy is stored in the form of pressure created by

the compressor, (which is then held in the receiver, distribution pipework and flexible supply

lines) it follows that if air is flowing then work is being done and energy will be used.

Therefore the stored energy will become less and the pressure will drop as energy is used.

Similarly, if we make it more difficult for air to flow by putting restrictions in the circuit, then

more work has to be done to overcome these difficulties. The more work that is done the

more energy is used and the greater the pressure drop.

These restrictions can take many forms - metal pipes, flexible hoses, threaded and quick

detachable connections, air filters, air regulators and of course the actual tool being used. In

all cases a restriction, by definition, impedes the flow of air by reducing the size of the

passageway available for the air to travel along. There is no pressure drop if air is not

flowing. It follows therefore that all air supply systems should be designed to have minimum



restrictions for the most effective use of the energy used in compressing the air in the first

place.

Lets examine each of these circuit components individually to find out how the best

equipment can be selected.

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4. Air Compressors

This is the machine that supplies air at a pressure and in a volume necessary to satisfy the

equipment. It takes a volume of air from the atmosphere at Atmospheric Pressure and

compresses it to a higher pressure.

Modern compressors are available in a variety of types, designed to suit many different users

requirements. They can be stand-alone electric motor compressor outfits or be self-contained

portable unit complete with petrol engine, air receiver and aftercooler. The outfits can be light

or heavy duty ranging from 1/3

rd

to 100 horsepower (HP) for home or factory use.

Note: Horse power (HP) here refers to the power rating of the electric motor, petrol or diesel

engine which drives a compressor. Alternatively motor size can be measured in Kilowatts

(kW). 1 HP = 0.75 kW

Compressed air is an expensive form of energy when compared with electricity, steam or

water power. Consequently, air compressors have to have good efficiency. Since a

compressor is designed to maintain an output volume of air per minute, its efficiency is called

Volumetric Efficiency. To define this better, we have to consider some facts about

compressor operation.

The performance of a compressor is expressed by 2 terms:

Displacement

This is the amount of air that a compressor can draw in for compression. The amount is

dependent on the physical make-up of the machinery itself, such as cylinder size and

revolutions per minute. For instance, if a piston compressor cylinder of 1 ft

3

capacity is

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cycling at 500 rpm (revolutions per minute), the displacement would be 500 cubic feet per

minute (500 cfm). Displacement is the theoretical performance if the compressor is 100%

perfect. However, like any other piece of machinery, it is actually less than 100% perfect

because of such losses as heat, friction, leakage etc.

Free Air Delivery (FAD)

Is the actual amount of air (cfm) that a compressor discharges. This is the amount of usable

air. FAD is always less than Displacement. The degree in which it is less is expressed as:

Volumetric Efficiency is the ratio of Delivery to Displacement.

e.g.

Displacement of 100 cfm : Free Air Delivery of 50 scfm

= Volumetric Efficiency of 50%

You should now understand that the best compressor is the most efficient. Consequently the

best is the one that performs with the least amount of air loss, or one with an efficiency of

80% or more. Compressors are precision built and care and expert advice should be taken

during their purchase.

The main considerations when selecting a compressor are:

.

1. Pressure developed (psi or bar)



2. Volume delivered (cfm or l/min)

It is not good practice to purchase a compressor to meet the minimum needs, one that has

excess capacity is better than one that is straining to keep up with demand. It is good

practise too, to anticipate future air needs when selecting a compressor so enough air is

available for extra spray guns and tools. It is important to keep in mind that the cost of

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compressed air is not the price of the compressor itself, but the operating cost (i.e.

electricity). It should be installed in an area where large volumes of cool, clean air is

available. This air is necessary as a supply for the compressor intake as well as for cooling

purposes.

Compressors naturally run warm or hot. The actual compressing process itself generates

heat. The compressor which runs the coolest is the most efficient unit. A compressor that is

never cleaned of dust, dirt or overspray, collects insulation that keep the heat within the

compressor. While installation is important to good operation, correct installation is equally

valuable to the life of a compressor.

Air Compressor Types

All compressors used in the spraying industry are of the Positive Displacementtype, that is,

successive volumes of air are confined within a closed space and then elevated to a higher

pressure. Several different types can be used, depending upon the size and type of work

being carried out.

Diaphragm Compressors

Confined to the home DIY market, these

units are fairly small, portable units with

only small output capabilities. Running

from single phase 220 v, these low cost

units have only small power output,

typically from 0.25-1 HP (0.18-0.75 kW),

giving very small air output of 1-4 cfm

(28-112 l/min). Due to their simple

design and construction they have only

approx. 60% efficiency.

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Piston Compressors

Available in a large range of size and

capacities, these are the most popular

type available and used around the world.

Their robust and simple construction has

made them extremely popular. Available

in portable or static versions, typically from

0.5-25 HP (0.375-18.75 kW) size.

However, much larger units are available

for factory installations. Higher efficiency

at 80-90%.



Sliding Vane Compressors

Rotary, positive displacement machines in which

axial vanes slide radially in a rotor mounted

eccentricity within a cylindrical casing. Available in

lubricated and non-lubricated construction, the

discharge air is normally free from pulsation

Suitable for larger air demands in bigger workshops,

these are normally fixed units powered by 3 phase

electricity (3-40 HP (2-30 kW)). Although a larger

capital outlay than Piston compressors, their quiet

operation and higher efficiency (70-80%) give more

economical day-to-day performance.

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Helical and Spiral Lobe

Compressors (Screw)

Rotary, positive displacement

machines in which two inter-meshing

rotors, each in helical configuration,

displace and compress the air. Similar

in capabilities to Vane type

compressors in lack of noise, lack of

pulsation and efficiency (80-90%),

they are normally regarded as the

best performance, but most

expensive, compressors available

today. Range of size available is

slightly larger than Vane type units (5-600 HP (3.75-450 kW)).

Care of Air Compressors

The design of modern compressors will give very high performance and long life, but only if

they are regularly checked and quickly repaired when necessary. While, in large factories,

there will be dedicated maintenance personnel to do this, smaller workshops or Bodyshops

will need to take out a service contract with their supplier.

Daily checks that can be carried out by the user include

a) draining accumulated moisture from air receivers and pulsation chambers,

b) checking oil levels in crank cases or cooling systems and

c) checking air intake and output filters for contamination levels.

The recommendations of the compressor manufacturer and supplier should always be

thoroughly investigated and then strictly followed.

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5. Compressed Air Dryers

Like compressors, these are specialised pieces of equipment that require professional

selection and maintenance for the best results. Removal of the moisture is important in order

to achieve the best quality paint finishes. Likewise removal of water will prevent corrosion

and swelling of air motor vanes in pneumatic sanders and rotary tools.

In addition, in the case of Breathing Air systems, there must be no free water in the airlines.

The dryers will remove moisture to a specified level called a Dew Point . This is the

temperature down to which the air would need to be cooled to precipitate any further

moisture out of it.

There are two main types in use today:



Refrigerated Dryers

In this type the incoming air is cooled until the moisture

vapour contained in it begins to precipitate - typically down

to just above the freezing point of water. The lower the

temperature, the more moisture will be precipitated. A

system very similar to a household refrigerator is used. To

warm the outgoing cold air it is passed through a heat

exchanger with the incoming warmer air (which also serves

to start cooling the incoming air). This type of drier functions

as a continuous process during the working day, having an

automatic water drain to get rid of the precipitated liquid.

Desiccant Dryers

Basically a container holding a quantity of drying agent or medium that has the ability to

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dehydrate air or other gas. Examples include Silica gel or activated alumina. The

compressed air stream to the tool is passed through the granules and moisture removed by

absorption without reducing the temperature. However, the most basic version of this type of

drier has no method of recycling the granules once they are fully saturated. Therefore the

complete contents of the container have to be changed

for new granules or the compressed air will be as moist

as if it had never passed through the dryer cylinder.

Larger and more expensive versions of this drier type

have methods of re-cycling the media built in to the

containers. In addition two cylinders are used - one to

remove moisture while the other is re-cycling. This

allows continuous moisture removal during the working

day. Most popular is the use of heater coils to warm up

the granules and re-vaporise the moisture of cylinder

No1 while No2 is doing its job. By using controlled

amounts of the incoming air this moisture is vented to

atmosphere before switching over to re-cycle No. 2

while No1 is working. Because this type of drier uses an

absorption process and not a precipitation process, it is possible to take the dew point down

to, typically, -1

o

C to -10

o

C.

It should be noted that both types of dryer are only designed to remove moisture. They do

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not have any effect on Carbon Monoxide, Carbon Dioxide, Hydrocarbons or even general

particulate contamination. To treat and eliminate these types of contaminant other equipment

and measures are necessary. In addition, the removal of too much

moisture from breathing air is as bad as having too much. Therefore the

full effects of a drier must be investigated before fitting them to the

compressed air system.

6. Compressed Air Receiver

This item absorbs pulsations in the discharge line from the compressor,

smooths the flow of air to the service lines and serves as a reservoir for

demands independent of the compressor output. In order to find the

required capacity of an air receiver, the compressor output and the

pattern of demand for air must be taken into account. As a guide to

sizing an air receiver, at normal compressor pressure the capacity of the

air receiver (in litres) should be between 6 and 10 times the free air

output of the compressor (litres/sec).

A further benefit of the receiver is that it precipitates condensate that



may be present in the air. This should be drained daily or as often as required. The air

receiver should be placed in the coolest possible location.

An air receiver must be fitted with a pressure relief valve, pressure gauge, inspection

openings, drain cock, identification and supporting feet. Sufficient external access must be

provided to allow visual inspection all around the air receiver shell.

7. Metal Air Supply Pipework

Compressed air hard pipework is necessary to distribute the air to all

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areas of the factory or bodyshop where it needs to be used. Long runs

of flexible hose are not recommended because of the possibility of

rapid deterioration and leakage. Supply pipework should be

constructed from Stainless Steel, ABS, Copper or Galvanised Steel.

As a guide, pipe diameters should never be smaller than the outlet of

the compressor or its air receiver. The largest internal diameters

practical and the shortest pipe runs possible will ensure the minimum

energy and pressure loss. In addition, bends should be the biggest radius

Recommended Air Supply Pipe Size

Compressor Size Minimum Recommended Compressor Pipe Size

Motor Output

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12-20 cfm

340-570 l/min

3/4 3/41 Not Rec.

5-10 HP

4-7.5 kW

20-40 cfm

570-1100 l/min

3/4 1 1 1/4 1 1/2

10-15 HP

7.5-11 kW

40-60 cfm

1100-1750 l/min

1 1 1 1/2 2

15-20 HP

11-15 kW

60-85 cfm

1750-2400 l/min

1 1 1/4 2 2 1/4

20-25 HP

15-18.5 kW

85-102

2400-3000 l/min

1 1/4 1 1/2 2 2 1/2

To avoid excessive pressure loss the pipe size should always be calculated to restrict the air

velocity to a maximum of 6 m/sec. As a guide, the air pipe should not be smaller than the outlet

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diameter of the compressor

practical as these will also create pressure loss. Routes from compressor to outlet point

should be as uncomplicated and simple as possible with the least bends, elbows or

junctions. The pipework should be constructed as a loop or Ring Main . In this format

compressed air can be drawn from two directions into the drop. The ring main should also be

sloped so that liquid condensate can gravity drain to chosen points in the system - drain legs

or the compressed air receiver. Take-off drops from the compressed air main should be

taken from the top of the pipe to avoid moisture gravity draining.

8. Air Management Systems- Regulators, Filters & Coalescers

There is one word in spray painting that sums up all of the factors and influences on results.

It is the word control. Control applies to all aspects of spray painting operations, such as

paint mixing, viscosity and spray technique. Here we are primarily concerned with the

consideration of air treatment and control.

Compressed air, which is the power in spraying, really needs control. Why? The air coming

out the compressor is usually raw i.e. it is basically untreated. It can be dirty, containing dust

particles and water vapour which condenses to liquid. It picks up rust scale from the inside of

the pipes and in some instances oil vapour from the compressor itself.



The air has to be regulated and cleaned, these are separate and distinct operations.

An Air Regulator unitis designed to take the pressure from the main compressed air

system and reduce it to a usable quantity. Regulators are available in different sizes

depending upon the work that they will be used for. Typically they are available in 0-4 bar, 0-6 bar and

0-8 bar output pressures. However, more importantly, they must also be selected

by the amount of compressed air volume that they can pass. Small units are suitable for

passing only small volumes of air, typically used for pressure feed tanks and applications that

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require air pressure to carry out the work. Medium and large units are used for tools that

need volume of air to do their jobs - like spray guns. It is important that the correct size

regulator is selected and purchased or spray equipment will neverwork correctly and at its

full potential.

Compressed air filterscome in several different forms. The most common types are the

common centrifugal/filter unit and the Oil Coalescer type. Centrifugal/filter units will normally

remove particulate contamination down to 50, 20 or 5 micron size, dependant upon the filter

element used. The construction of the filter element may be as simple as a Cotton Wool,

fibrous, type. However, nowadays they are usually they are made from sintered Bronze

particles, allowing them to be cleaned and re-used to lengthen their service life.

A Filter Regulator unit(sometimes called an Air

Transformer) is a combination unit which has both a

Regulator and Filter built into the same body. These

are extremely popular for general compressed air use

and control.

For finer filtration and cleaning a Coalescer unit is

necessary. These haveto be used on compressed

breathing air systems to comply with British and

European requirements, however increasing amounts

of customers are fitting such units to their spraying air

systems for critical finishing operations. Coalescers

have the ability to filter oil and particulate

contamination down to 0.01 micron diameter. Again,

all filter unit types are available in different sizes for different applications.

It must be appreciated however, that the smaller the filtration size, the quicker it will become

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blocked. Therefore a pre-filter unit of a larger filtration size is recommended to be fitted

before a coalescer. In addition, the smaller the filter element orifice, the larger the pressure

drop across it. Always select and use the correct units necessary for the application being

carried out.



DeVilbiss DVFR Range

DVFR-1

Air Inlet Thread: 1/2 BSP

Air Outlet Thread: 1/4 BSP

Max Air Flow: 90 cfm (2550 Ltr/min)

Max Inlet Press: 190 psi (13 bar)

Outlet Pressure: 0-116 psi (0-8 bar)

Max op. Temp: 100

o

C (212

o

F)

Pressure Gauge: 0-160 psi (0-11 bar)

Filter Element: 5 micron

Drain Valve: Semi-Automatic

DVFR-2




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Max op. Temp: 100

o

C (212

o

F)



Coalescer Filtration: 99.99% at 0.01 micron


DVFR-3






Max op. Temp: 40

o

C (104

o

F)




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DVFR-4






Max op. Temp: 40

o

C (104

o

F)






DeVilbiss DVFR-2 Filter/Regulator/Coalescer Operation

Compressed air from the main supply enters the end block entry port on the left. The higher

the mains pressure is, then the greater the volume of air that will be able to be forced through

the complete assembly and on to the equipment. Treating the three sections separately, the

following things then happen.

Filter Unit

Immediately after entering the filter unit body the air

moves downward and has to pass through a set of

45

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o

angled deflector vanes (not shown in the

drawing). These deflectors cause the air to spin

around the inside of the filter bowl casing at high

speed. The centrifugal force generated throws out

the heaviest liquid and particulate contamination

against the inside of the bowl where can fall down,

past the umbrella , into the bottom chamber where

it accumulates. The moving air stream then has to

move upward again and pass through the sintered

bronze filter, which will take out any particulate

contamination down to a size of 5 micron. Air then

can pass through the gap of the open regulator

valve (see regulator operation) and out of the filter

regulator body.

The filter bowl is fitted with an Aluminium internal liner, and not the normal clear

polycarbonate type, making the unit suitable for installation inside combined

spraybooth/ovens where the temperatures can rise to 80

o

C.

Regular draining of the bowl is necessary, particularly in hot weather, or excessive build up

of liquid may cause a carry over , negating the liquid droplet filtering ability of the unit.

Regulator Unit

By rotating the control knob clockwise and

compressing the spring, pressure is applied to the

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diaphragm plate which is pushed down and, in turn,

presses down on the valve body and opens the

regulator valve. Air flows through the open valve and

out of the regulator body. As the air moves through the

valve and out of the body it also passes up a small

bleed hole to the underside of the diaphragm and

diaphragm plate. When the pressure of this air bleedoff equals the spring pressure then the diaphragm

and

plate will be lifted and the valve will close. Any demand

of air by equipment will reduce the pressure of the

main airstream and bleed-off air, allowing the main

spring pressure to open the valve again.

The regulator is a self-relieving type, meaning that if

the regulator knob is rotated anti-clockwise to reduce

the pressure then the excess pressure will be vented

by the regulator without the necessity to pull the trigger

of the spray gun. The reduction of downward spring

pressure allows the higher air pressure to lift the

diaphragm plate off of the top of the valve body. The

excess internal air pressure can then bleed off to

atmosphere via the small hole in the centre of the diaphragm plate. When spring and internal

air pressures again equalise the diaphragm plate will fall and close off the bleed hole.



The regulator knob can be locked in place by firmly pushing down on the knob top. This will

help stop accidental or deliberate pressure alteration. The knob can be unlocked by firmly

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pulling it up.

Coalescer Unit

Air enters the body and flows down into the centre of the

coalescer cartridge. Firstly it passes through a closely

woven microfibre layer that will filter out very small oil

droplets that have managed to get past the previous

centrifugal force and 5 micron filter of the filter module.

The efficiency of this fibrous membrane gives a 99.99%

filtration down to 0.01 microns, suitable for breathing

quality air. The movement of the air stream pushes the

oil droplets to the outer foam layer gradually coalescing

into larger droplets and falling into the bowl. Clean air

can now pass upwards and out of the coalescer module

to the manifold block and air outlet valves. Because all of

the liquid filtered out by the coalescer cartridge can be

removed during draining the cartridge should, in theory,

last forever. However, it also filters out very small

particulate contamination that will gradually clog the microfibres, requiring periodic changing

of the cartridge.

Semi-Automatic drains

The drain valves fitted to the filter and coalescer bowls will be held closed (i.e. not draining)

by the air pressure in the bowl. If the air supply to the filter/regulator/coalescer unit is shut off

(by closing a valve or turning the compressor off) then the air pressure will be removed and

the bottom drain valves will open, allowing accumulated liquid to drain out. Alternatively, the

drain valves may be manually opened, by pushing them up against internal air pressure,

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allowing liquid to drain out.

9. Hoses

The performance of spray and air tools is dependant upon receiving air and/or material at

specified pressures and in adequate volumes. A hose and its fittings can be the weakest link

in any system. Improper selection and/or maintenance of a hose can create a number of

problems.

Construction

A hose is normally a performance designed combination of 3 components:

Inner Tube

This is an inner liner that carries air or material from one end of the hose to the other. In

specialist hoses the liner has to have chemical and abrasion resistance to the material that

will be transported through it. The quality of surface finish inside the liner is very important as

the smoother the liner - the lower the friction and pressure loss. The inside diameter of the

liner is also important - the larger the diameter - the easier air will flow and the smaller the

pressure loss.

Reinforcement

This adds strength to the hose, and is normally located between the inner tube and outer

cover. It can use several different combinations of reinforcement design and material type

that will determine the hose pressure rating, flexibility, kink and stretch resistance and

coupling retention. Normal low-pressure hoses will use a nylon or cotton type woven braid,

while high-pressure hoses use a reinforced steel mesh for strength.



Cover

This is the outer skin of the hose. It protects the reinforcement by preventing contact with

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oils, moisture, chemicals and abrasive surfaces. The cover does not contribute to hose

performance or characteristics, it only protects the reinforcement which is the hoses strength.

The cover may be colour coded to visually indicate the material being transported inside, and

will also normally have identification Part numbers and pressure ratings marked on it.

Note:Under no circumstances is air hose to be used for Solvents and/or Solvent based

materials. The liner is not designed for liquids. Likewise it must be remembered that, while

they are solvent resistant, the exterior covers of fluid lines are not designed for immersion in

solvents or paints.

Hose Types

DeVilbiss Red Rubber Air Hose

H-1957

1

/4 6.4 mm

I

/

D

, H-1921

5

/16 8.0 mm

I

/

D

, H-1958

3

/8

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9.6 mm

I

/

D

Max. press. 250 psi

Synthetic Rubber compound tube for excellent oil and water

resistance. Reinforced high tensile strength braid for

flexibility. Perforated synthetic rubber compound cover for resistance to oil, weathering,

ozone and abrasion. A heavy duty air hose suitable for arduous spraying environments in

manual spraying operations. Although heavier in weight than its Vinyl counterparts it has

better solvent, slash and temperature resistance.

DeVilbiss Red Line & Euroline Air Hose

H-2397

1

/4 6.4 mm

I

/

D

, H-2398

5

/16 8.0 mm

I

/

D

, H-2399

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3

/8

9.6 mm

I

/

D

Max. pressure 200 psi

PVC (Polyvinylchloride) tube for flexibility, water/oil

resistance and superior smooth bore finish. High tensile

Polyamide yarn reinforcement for flexibility and pressure

strength retention. Polyurethane outer cover for kink/scuff

resistance and solvent/oil resistance. A lightweight hose for general-purpose use in spray

shops. Its flexibility and lightness keeps operator fatigue to a minimum and makes it popular

with sprayers.

Nylon Air & Fluid Hose

Concentric seamless extruded construction and can be

made in many different colours for easy identification.

Translucent, clear white (actually slightly cream colour) is

often used due to the ability to see liquids moving through

the hose interior. This is durable, lightweight and flexible

although prone to kinking when bent in tight radii. Typically used on automatic spraying



machines, where the fluid or air has to be fed to spray guns which are often in constant rapid

motion. Unaffected by most paints and solvents, Nylon hose can also double as fluid hose,

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although it will tend to be stained by the fluids pigment over extended use.

Polythene Air/Fluid Hose

Often used as an alternative to Nylon hose and also

recommended for use with automatic and electrostatic spray

equipment. Suitable for conveying most gasses, paints and

solvents and can be used for water based materials. It is

durable and slightly more flexible than nylon hose, although

still prone to kinking in tight radii. Concentric seamless construction and also available in

various colours.

Air Hose Pressure Loss

This is the loss of air or material pressure due to friction (caused by air or material flow)

between the source and the point of use. As the air or material travels through the hose or

pipe it rubs against the walls, losing energy and pressure as it goes. The table below

indicates just how much pressure drop can be expected at different pressures with hoses of

varying length and internal diameters. At low pressures and short lengths of hose this drop is

not particularly significant, but as the pressure increases and hose lengthened, the pressure

drop rapidly becomes very large and must be compensated for. Far too often a tool or gun is

blamed for malfunctioning when the real cause is an inadequate supply of compressed air or

material resulting from using too small inside diameter hose.

Hose outlet / Gun Handle Inlet Pressure

Air Hose

Internal

Diameter

Regulator

Pressure

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5 metre

(16 ft)

10 metre

(33 ft)

15 metre

(49 ft)

6 mm (1/4 ) 3 bar (45 psi) 1.1 bar (16 psi) 0.8 bar (12 psi) 0.6 bar (9 psi)




8 mm (5/16 ) 3 bar(45 psi) 1.8 bar (26 psi) 1.5 bar (22 psi) 1.4 bar (20 psi)






10 mm (3/8 ) 5 bar (75 psi) 3.4 bar (50 psi) 3.3 b ar (48 psi) 3.1 bar (45 psi)


Above data compiled using DeVilbiss DVFR-4 Regulator, H-1975, H-1921 and H-1958 rubber hose fitted

with

re-usable hose fittings, MPV-10 male and MPV-424 female Q/D connectors, GFHV-510 with 153 air cap.

Inlet

pressure at DVFR-4 = 100 psi (6.9 bar).

For all spray guns it is recommended that a minimum of 8 mm (5/16 ) bore hose be used due to the

high

volumes of air used and the high-pressure drops generated. With a hose length of 7 metres (23 ft) or

greater

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10 mm (3/8 ) bore hose should be used.

When using air hoses greater than 10 m (33 ft) long it is expected that a rapid choking effect will be

experienced when the gun is triggered.

Every air hose type will have different air flow characteristics and pressure drop depending

upon the materials and quality of manufacture. Therefore the hose length, inside diameter

and quality must be considered before purchase and use for a particular job.



Hose Connections

There are several types of flexible hose end connector available today.

Non-reusable Crimp style Non-reusable Oetiker clip type

Re-usable Jubilee clip type Re-usable ferrule type

In all cases the correct sized connector

and clip/crimp fitting must be used for

the hose selected. Failure to do so will

not only cause a connection that will

not equal the pressure rating of the

hose but will also be a safety hazard,

endangering sprayers during use.

The Crimp, Jubilee and Oetiker types

are cheaper to purchase but tend to be

damaged more easily, and need

replacing more often, than the more

expensive re-usable versions. In

addition, re-usable connectors,

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because they are made for a specific

size hose and type, will be designed to give the maximum airflow and minimum pressure loss

possible. All too commonly, through lack of range available or lack of knowledge of the

purchaser, the wrong connector of the other styles are used, creating problems and air

starvation.

In addition to connector type consideration must be made to the method of hose termination -whether

it is to be threaded or Quick Detachable (Q/D). Thread size and style normally fall

into the following trends.

Thread used

on Gun

U.K. USA Germany France BeNeLux Middle

East

Scandanavia

Fluid

Connector

3/8

BSP (M)

3/8

NPS (M)

3/8

BSP (M)

3/8

BSP (M)

3/8

BSP (M)

3/8

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NPS (M)

3/8

NPS (M)

Air Connector 1/4

BSP (M)

1/4

NPS (M)

1/4

BSP (M)

1/4

BSP (M)

1/4

BSP (M)

1/4

NPS (M)

1/4

NPS (M)

These are the thread forms traditionally used on low-pressure spray equipment. However,

occasionally, Metric threads are used - watch out!

Quick Detachable Connectors (Q/D s)

There are many types of Q/D connector available from

many different sources. The particular manufacturer of your

connectors is not as important as their design. Q/D s with

small central holes (4 mm dia or less) can create severe

pressure loss. By using Q/D s with 5mm holes or larger

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these losses will be minimised, allowing the air tools to

have sufficient energy to work correctly. Both the DeVilbiss

MPV and PA Series connectors have this size orifice, plus

the MPV Series are a European standard external profile -available and used on spray equipment all over

Europe.



Hose Care, Storage & Inspection

The hose has been designed to minimise the effects of cutting,

abrasion, pulling and kinking. Nevertheless, precautions should

be taken when using the hose. It must be used at or below the

specified working pressure, and changes in pressure should be

made gradually to eliminate excessive surging. It should not be

mishandled by kinking or running equipment over it, nor dragged

over abrasive surfaces. By handling the hose properly you can

extend its working life. Inspect it periodically for worn covers that

expose the reinforcement, expanded areas in the hose, blisters

in the cover and softening and compressed areas caused by

kinks. If these problems are found on high-pressure airless hose. The hose must be

replaced to avoid possible hazards. However standard pressure hose can be repaired by

cutting out the problem areas and installing splicers or connections. Hose that appears to be

softened by exposure to solvents, chemicals and/or heat may not be suitable for its specific

use. Hose connectors should be periodically inspected to ensure that they are secure to the

hose and that they have not caused cuts or damage to the hose. Threads should be checked

for damage or contamination or difficulties will be found attaching them to the equipment..

Q/D male stems should fit securely in their female connectors and lock in place. Hoses

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should be stored un-pressurised in flat coils, in a cool and dry area. Avoid tying hose with

wire.

10. Equipment Air Consumption

Below are shown some typical air consumptions for different types of pneumatic equipment.

You can see that there is a wide range of consumptions possible. Included in the table are

the equivalent air compressor sizes necessary to supply just that type of equipment. The

power requirement can sometimes be surprisingly large! The above HP s are based on 1HP

= 0.75 Kw = 4.5 cfm, the typical performance of a good piston or screw compressor.

However, with a screw type compressor of slightly lesser efficiency the chart would need to

be recalculated on a basis of 1HP = 0.75 Kw = 3.3 cfm making the power requirement even

larger!

Typical Air Consumption Approx. Compressor Power

Needed

Tool l/min cfm kW HP

DA Sander 425 15 2.5 3.3

Air Duster 480 17 2.8 3.8

Polisher 480-708 17-25 2.8-4.2 3.8-5.6

Shot Blaster 2280 80.5 13.3 17.9

DeV. MPV Full Face Air Mask 180 6.3 1 1.4

DeV. MPV Half mask Air Mask 100 3.5 0.6 0.8

DeV. JGA Suction or GFG Conventional gun 275-345 9.7-12.2 1.6-2 2.2-2.7

DeV. JGA Pressure Gun 232-680 8.2-24 1.3-4 1.8-5.3

DeV. MP Gravity Touch-in gun 25-58 0.88-2.05 0.2-0.4 0.2-0.5

DeV. MPS Gravity Touch-in gun 94-110 3.3-3.9 0.5-0.7 0.73-0.9

DeV. MTG Mid size gun 70-143 2.5-5 0.4-0.8 0.6-1.1

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DeV. FLG Conventional Low cost gun 350 12.4 2.1 2.8

DeV. GTI Suction or GTI Gravity HVLP gun 425-453 15-16 2.5-2.7 3.3-3.6

DeV. EGHV Touch-in gun 122 4.3 0.75 1

DeV. FLG HVLP Low cost gun 410 14.5 2.4 3.2

DeV. GTI Pressure gun 425-510 15-18 2.5-3 3.3-4

DeV. KBII Pressure Feed Cup 0 0 0 0

DeV. 10Ltr & 20Ltr Pressure Feed Tanks 0 0 0 0

Airbrush 5.6-17 0.2-0.6 0.03-0.1 0.04-0.13





Gun Set-up Airflow l/min (cfm) A

psi

B

psi

C

psi

D

psi

E

psi

F

psi

5 23 28 34 49 30 100 air cap + any

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GTI-213 tip 453 (16) 10 36 42 51 60 50



DeVilbiss DVFR-2 Filter/Regulator/Coalescer



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Bournemouth

Dorset

England

BH11 9LH

Tel: 00 44 (0)1202 571111

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