air supply 2

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COMPRESSED AIR PAGE 1


Compressed AirSupply

Training Notes

Trainee: ...

Course Date: ..

SJM IssB June99


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A. CONTENTS

SECTION SUBJECT PAGE

1. Introduction 32. Units of Pressure 33. The Compressed Air Circuit 44. Air Compressors 5

Displacement 5Free Air Delivery 5Air Compressor Types 6Diaphragm Compressors 6Piston Compressors 6Sliding Vane Compressors 7Helical & Spiral Lobe Compressors (Screw) 7Care of Compressors 7

5. Compressed Air Dryers 7Refrigerated Dryers 7Desiccant Dryers 8

6. Compressed Air Receiver 87. Metal Air Supply Pipework 98. Air Management Systems 9

DeVilbiss DVFR Range 11DeVilbiss DVFR-2 Filter/Regulator/Coalescer Operation 12Filter Unit 12Regulator Unit 12Coalescer Unit 13Semi-Auto Drains 13

9. Hoses 13Construction 13Inner Tube 13Reinforcement 13Cover 14Hose Types 14DeVilbiss Red Rubber Air Hose 14DeVilbiss Red Line & Euroline Air Hose 14Nylon Air & Fluid Hose 14Polythene Air/Fluid Hose 15Air Hose Pressure Loss 15Hose Connections 16Quick Detachable Connections (Q/Ds) 16Hose Care, Storage & Inspection 17

10. Equipment Air Consumption 17Pressure drop in a Conventional Gun Air System 18Pressure drop in a GTI Gun Air System 19Sectioned drawing of a DeVilbiss DVFR-2 20


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1. IntroductionThe process of spraying is most simply defined as a mechanical means of applyingmaterial. Mechanical because either automatic or manual machines (i.e. spray guns) areproviding 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 givensurface and the tools used to do it. The primary tool we will use is a Spray Gun and thematerial to be sprayed is normally Paint.

The minimum amount of equipment required to carry out this depends upon the particularmaterial 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 Unit4. 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 systemand the benefits that can be obtained by choosing and using the correct basic equipment.

2. Units of PressureA compressed air system always forms a complete circuit,beginning and ending with atmospheric air pressure. This is usuallyassumed to be between 14.7 - 15 Pounds per Square Inch (psi) orapproximately 1 Atmosphere. Alternatively this pressure is known

as 1 Bar. Atmospheric air pressure will slightly change dependingupon the weather condition being experienced at a particular time.Look at the weather forecast on the television - you will see curvedlines joining points of equal atmospheric pressure (called Isobars)marked on the map - marked in millibar (mbar or 1000 ths of aBar). In the British Isles the atmospheric pressure typically variesfrom 980 to 1030 mbar. However, because atmospheric pressure is always around us, and itvaries (relatively) only very little, we tend to ignore it, and therefore calibrate our pressuregauges 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 ofMetric units, and depending upon where you are in the World several different units may beused.

14.7 psi = 1 bar = 100 kPa = 1 kg/cm2= 750 mm Mercury


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3. The Compressed Air CircuitThe air is taken into the compressor and work is done when compressing the air, normally bya factor of 8:1 or 10:1, depending on the specification and performance of the compressor.

The energy involved incompressing the air istransferred from the powersource, e.g.: electric motor orinternal combustion engine,to the air in the form of thepressurisation process. In aperfect world the transfer ofenergy would be 100%, butin fact it is considerably less.This is the first point in thecircuit where work is doneand energy is consumed.The amount of energy used

will depend not only on thefinal pressure but also on thevolume 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 willflow 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 f itted and used. Its purpose is to reduce the input air pressuresupplied (anything up to 200 psi in normal working conditions) to a usable pressure ofbetween 1 psi to 90 psi at its output and maintain that pressureconstantly. This will only be possible if:

a) the compressor maintains the line pressure above the requiredregulator output pressure, and

b) the air regulator is capable of handling the volume of air beingdemanded by the user tool.

The regulator output pressure is transferred via flexible supplyhoses to the tool - the spray gun, sander etc. Air will flow alongthe lines until the pressure in them has built up to the regulatorpressure. Again, while the air is flowing, work will be done andenergy will be used up.

It is important to note that onlywhen air is flowing is work beingdone, and energy used up. Because the energy is stored in the form of pressure created bythe compressor, (which is then held in the receiver, distribution pipework and flexible supplylines) 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, thenmore work has to be done to overcome these difficulties. The more work that is done themore energy is used and the greater the pressure drop.

These restrictions can take many forms - metal pipes, flexible hoses, threaded and quickdetachable connections, air f ilters, air regulators and of course the actual tool being used. Inall cases a restriction, by definition, impedes the flow of air by reducing the size of thepassageway available for the air to travel along. There is no pressure drop if air is notflowing. It follows therefore that all air supply systems should be designed to have minimum


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

Lets examine each of these circuit components individually to find out how the bestequipment can be selected.

4. Air CompressorsThis is the machine that supplies air at a pressure and in a volume necessary to satisfy theequipment. It takes a volume of air from the atmosphere at Atmospheric Pressure andcompresses it to a higher pressure.

Modern compressors are available in a variety of types, designed to suit many different usersrequirements. They can be stand-alone electric motor compressor outfits or be self-containedportable unit complete with petrol engine, air receiver and aftercooler. The outfits can be lightor heavy duty ranging from 1/3rdto 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 orwater power. Consequently, air compressors have to have good efficiency. Since acompressor is designed to maintain an output volume of air per minute, its eff iciency is calledVolumetric 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 isdependent on the physical make-up of the machinery itself, such as cylinder size andrevolutions per minute. For instance, if a piston compressor cylinder of 1 f t3capacity iscycling at 500 rpm (revolutions per minute), the displacement would be 500 cubic feet perminute (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% perfectbecause 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 usableair. 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 thebest is the one that performs with the least amount of air loss, or one with an eff iciency of80% or more. Compressors are precision built and care and expert advice should be takenduring their purchase.

The main considerations when selecting a compressor are: .1. Pressure developed (psi or bar)


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2. Volume delivered (cfm or l/min)

It is not good practice to purchase a compressor to meet the minimum needs, one that hasexcess capacity is better than one that is straining to keep up with demand. It is goodpractise too, to anticipate future air needs when selecting a compressor so enough air isavailable for extra spray guns and tools. It is important to keep in mind that the cost ofcompressed 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 isavailable. This air is necessary as a supply for the compressor intake as well as for coolingpurposes.

Compressors naturally run warm or hot. The actual compressing process itself generatesheat. The compressor which runs the coolest is the most efficient unit. A compressor that isnever cleaned of dust, dirt or overspray, collects insulation that keep the heat within thecompressor. While installation is important to good operation, correct installation is equallyvaluable to the life of a compressor.

Air Compressor TypesAll 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 higherpressure. Several different types can be used, depending upon the size and type of workbeing carried out.

Diaphragm CompressorsConfined to the home DIY market, theseunits are fairly small, portable units withonly small output capabilities. Runningfrom single phase 220 v, these low costunits 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 simpledesign and construction they have onlyapprox. 60% efficiency.

Piston CompressorsAvailable in a large range of size andcapacities, these are the most populartype available and used around the world.Their robust and simple construction hasmade them extremely popular.Available

in portable or static versions, typically from0.5-25 HP (0.375-18.75 kW) size.However, much larger units are availablefor factory installations. Higher efficiencyat 80-90%.


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Sliding Vane CompressorsRotary, positive displacement machines in whichaxial vanes slide radially in a rotor mountedeccentricity within a cylindrical casing. Available inlubricated and non-lubricated construction, thedischarge air is normally free from pulsationSuitable for larger air demands in bigger workshops,these are normally f ixed units powered by 3 phaseelectricity (3-40 HP (2-30 kW)). Although a largercapital outlay than Piston compressors, their quietoperation and higher efficiency (70-80%) give moreeconomical day-to-day performance.

Helical and Spiral LobeCompressors (Screw)Rotary, positive displacementmachines in which two inter-meshing

rotors, each in helical configuration,displace and compress the air. Similarin capabilities to Vane typecompressors in lack of noise, lack ofpulsation and efficiency (80-90%),they are normally regarded as thebest performance, but mostexpensive, compressors availabletoday. Range of size available isslightly larger than Vane type units (5-600 HP (3.75-450 kW)).

Care of Air CompressorsThe design of modern compressors will give very high performance and long life, but only ifthey are regularly checked and quickly repaired when necessary. While, in large factories,there will be dedicated maintenance personnel to do this, smaller workshops or Bodyshopswill 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 andc) checking air intake and output filters for contamination levels.

The recommendations of the compressor manufacturer and supplier should always bethoroughly investigated and then strictly followed.

5. Compressed Air DryersLike compressors, these are specialised pieces of equipment that require professionalselection and maintenance for the best results. Removal of the moisture is important in orderto achieve the best quality paint finishes. Likewise removal of water will prevent corrosionand 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 thetemperature down to which the air would need to be cooled to precipitate any furthermoisture out of it.There are two main types in use today:


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Refrigerated DryersIn this type the incoming air is cooled until the moisturevapour contained in it begins to precipitate - typically downto just above the freezing point of water. The lower thetemperature, the more moisture will be precipitated. Asystem very similar to a household refrigerator is used. Towarm the outgoing cold air it is passed through a heatexchanger with the incoming warmer air (which also servesto start cooling the incoming air). This type of drier functionsas a continuous process during the working day, having anautomatic water drain to get rid of the precipitated liquid.

Desiccant DryersBasically a container holding a quantity of drying agent or medium that has the ability todehydrate air or other gas. Examples include Silica gel or activated alumina. Thecompressed 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 ofdrier has no method of recycling the granules once they are fully saturated. Therefore thecomplete contents of the container have to be changedfor new granules or the compressed air will be as moistas if it had never passed through the dryer cylinder.Larger and more expensive versions of this drier typehave methods of re-cycling the media built in to thecontainers. In addition two cylinders are used - one toremove moisture while the other is re-cycling. Thisallows continuous moisture removal during the workingday. Most popular is the use of heater coils to warm upthe granules and re-vaporise the moisture of cylinder

No1 while No2 is doing its job. By using controlledamounts of the incoming air this moisture is vented toatmosphere before switching over to re-cycle No. 2while 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 downto, typically, -1oC to -10oC.

It should be noted that both types of dryer are only designed to remove moisture. They donot have any effect on Carbon Monoxide, Carbon Dioxide, Hydrocarbons or even generalparticulate contamination. To treat and eliminate these types of contaminant other equipmentand measures are necessary. In addition, the removal of too muchmoisture from breathing air is as bad as having too much. Therefore the

full effects of a drier must be investigated before fitting them to thecompressed air system.

6. Compressed Air ReceiverThis item absorbs pulsations in the discharge line from the compressor,smooths the flow of air to the service lines and serves as a reservoir fordemands independent of the compressor output. In order to find therequired capacity of an air receiver, the compressor output and thepattern of demand for air must be taken into account. As a guide tosizing an air receiver, at normal compressor pressure the capacity of theair receiver (in litres) should be between 6 and 10 times the free airoutput of the compressor (litres/sec).A further benefit of the receiver is that it precipitates condensate that


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may be present in the air. This should be drained daily or as often as required. The airreceiver should be placed in the coolest possible location.An air receiver must be fitted with a pressure relief valve, pressure gauge, inspectionopenings, drain cock, identification and supporting feet. Sufficient external access must beprovided to allow visual inspection all around the air receiver shell.

7. Metal Air Supply PipeworkCompressed air hard pipework is necessary to distribute the air to allareas of the factory or bodyshop where it needs to be used. Long runsof flexible hose are not recommended because of the possibility ofrapid deterioration and leakage. Supply pipework should beconstructed from Stainless Steel, ABS, Copper or Galvanised Steel.As a guide, pipe diameters should never be smaller than the outlet ofthe compressor or its air receiver. The largest internal diameterspractical and the shortest pipe runs possible will ensure the minimumenergy and pressure loss. In addition, bends should be the biggest radius

Recommended Air Supply Pipe Size

Compressor Size Minimum Recommended Compressor Pipe SizeMotor Output


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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 airsystem and reduce it to a usable quantity. Regulators are available in different sizesdepending 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 selectedby the amount of compressed air volume that they can pass. Small units are suitable forpassing only small volumes of air, typically used for pressure feed tanks and applications thatrequire air pressure to carry out the work. Medium and large units are used for tools thatneed volume of air to do their jobs - like spray guns. It is important that the correct sizeregulator is selected and purchased or spray equipment will neverwork correctly and at itsfull potential.

Compressed air filterscome in several different forms. The most common types are thecommon centrifugal/filter unit and the Oil Coalescer type. Centrifugal/filter units will normallyremove particulate contamination down to 50, 20 or 5 micron size, dependant upon the filterelement 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 Bronzeparticles, allowing them to be cleaned and re-used to lengthen their service life.

A Filter Regulator unit(sometimes called an AirTransformer) is a combination unit which has both aRegulator and Filter built into the same body. Theseare extremely popular for general compressed air useand control.

For finer filtration and cleaning a Coalescer unit isnecessary. These haveto be used on compressedbreathing air systems to comply with British and

European requirements, however increasing amountsof customers are fitting such units to their spraying airsystems for critical finishing operations. Coalescershave the ability to filter oil and particulatecontamination down to 0.01 micron diameter. Again,all fi lter 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 becomeblocked. Therefore a pre-filter unit of a larger filtration size is recommended to be fittedbefore a coalescer. In addition, the smaller the f ilter element orifice, the larger the pressuredrop across it. Always select and use the correct units necessary for the application beingcarried out.


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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: 100oC (212

oF)

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

Filter Element: 5 micron

Drain Valve: Semi-Automatic

DVFR-2



Max Air Flow: 50 cfm (1415 Ltr/min)

Max Inlet Press: 190 psi (13 bar)



oF)



Coalescer Filtration: 99.99% at 0.01 micron


DVFR-3Air Inlet Thread: 1/2 BSP






oF)




DVFR-4







oF)





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DeVilbiss DVFR-2 Filter/Regulator/Coalescer OperationCompressed air from the main supply enters the end block entry port on the left. The higherthe mains pressure is, then the greater the volume of air that will be able to be forced throughthe complete assembly and on to the equipment. Treating the three sections separately, thefollowing things then happen.

Filter Unit

Immediately after entering the filter unit body the airmoves downward and has to pass through a set of45o angled deflector vanes (not shown in thedrawing). These deflectors cause the air to spinaround the inside of the filter bowl casing at highspeed. The centrifugal force generated throws outthe heaviest liquid and particulate contaminationagainst the inside of the bowl where can fall down,past the umbrella, into the bottom chamber whereit accumulates. The moving air stream then has to

move upward again and pass through the sinteredbronze filter, which will take out any particulatecontamination down to a size of 5 micron. Air thencan pass through the gap of the open regulatorvalve (see regulator operation) and out of the filterregulator body.The filter bowl is fitted with an Aluminium internal liner, and not the normal clearpolycarbonate type, making the unit suitable for installation inside combinedspraybooth/ovens where the temperatures can rise to 80oC.Regular draining of the bowl is necessary, particularly in hot weather, or excessive build upof liquid may cause a carry over, negating the liquid droplet filtering ability of the unit.

Regulator UnitBy rotating the control knob clockwise andcompressing the spring, pressure is applied to thediaphragm plate which is pushed down and, in turn,presses down on the valve body and opens theregulator valve. Air flows through the open valve andout of the regulator body. As the air moves through thevalve and out of the body it also passes up a smallbleed hole to the underside of the diaphragm anddiaphragm plate. When the pressure of this air bleed-off equals the spring pressure then the diaphragm andplate will be lifted and the valve will close. Any demand

of air by equipment will reduce the pressure of themain airstream and bleed-off air, allowing the mainspring pressure to open the valve again.The regulator is a self-relieving type, meaning that ifthe regulator knob is rotated anti-clockwise to reducethe pressure then the excess pressure will be ventedby the regulator without the necessity to pull the triggerof the spray gun. The reduction of downward springpressure allows the higher air pressure to lift thediaphragm plate off of the top of the valve body. Theexcess internal air pressure can then bleed off to

atmosphere via the small hole in the centre of the diaphragm plate. When spring and internalair pressures again equalise the diaphragm plate will fall and close off the bleed hole.


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The regulator knob can be locked in place by firmly pushing down on the knob top. This willhelp stop accidental or deliberate pressure alteration. The knob can be unlocked by firmlypulling it up.

Coalescer UnitAir enters the body and flows down into the centre of thecoalescer cartridge. Firstly it passes through a closelywoven microfibre layer that will filter out very small oildroplets that have managed to get past the previouscentrifugal 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 breathingquality air. The movement of the air stream pushes theoil droplets to the outer foam layer gradually coalescinginto larger droplets and falling into the bowl. Clean aircan now pass upwards and out of the coalescer moduleto the manifold block and air outlet valves. Because all of

the liquid filtered out by the coalescer cartridge can beremoved 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 changingof the cartridge.

Semi-Automatic drainsThe 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 andthe bottom drain valves will open, allowing accumulated liquid to drain out. Alternatively, thedrain valves may be manually opened, by pushing them up against internal air pressure,

allowing liquid to drain out.

9. HosesThe performance of spray and air tools is dependant upon receiving air and/or material atspecified pressures and in adequate volumes. A hose and its fittings can be the weakest linkin any system. Improper selection and/or maintenance of a hose can create a number ofproblems.

ConstructionA 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. Inspecialist hoses the liner has to have chemical and abrasion resistance to the material thatwill be transported through it. The quality of surface finish inside the liner is very important asthe smoother the liner - the lower the friction and pressure loss. The inside diameter of theliner is also important - the larger the diameter - the easier air will flow and the smaller thepressure loss.

ReinforcementThis adds strength to the hose, and is normally located between the inner tube and outercover. It can use several different combinations of reinforcement design and material typethat will determine the hose pressure rating, flexibility, kink and stretch resistance andcoupling 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.


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Cover

This is the outer skin of the hose. It protects the reinforcement by preventing contact withoils, moisture, chemicals and abrasive surfaces. The cover does not contribute to hoseperformance 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, andwill 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 basedmaterials. The liner is not designed for liquids. Likewise it must be remembered that, whilethey are solvent resistant, the exterior covers of fluid lines are not designed for immersion insolvents or paints.

Hose Types

DeVilbiss Red Rubber Air Hose

H-1957 1/4 6.4 mmI/D, H-1921

5/168.0 mmI/D, H-1958

3/89.6 mm I/DMax. press. 250 psiSynthetic Rubber compound tube for excellent oil and waterresistance. Reinforced high tensile strength braid forflexibility. Perforated synthetic rubber compound cover for resistance to oil, weathering,ozone and abrasion. A heavy duty air hose suitable for arduous spraying environments inmanual spraying operations. Although heavier in weight than its Vinyl counterparts it hasbetter solvent, slash and temperature resistance.

DeVilbiss Red Line & Euroline Air Hose

H-2397 1/4 6.4 mmI/D, H-2398

5/168.0 mmI/D, H-2399

3/89.6 mm I/DMax. pressure 200 psiPVC (Polyvinylchloride) tube for flexibility, water/oilresistance and superior smooth bore finish. High tensilePolyamide yarn reinforcement for flexibility and pressurestrength retention. Polyurethane outer cover for kink/scuffresistance and solvent/oil resistance. A lightweight hose for general-purpose use in spray

shops. Its f lexibility and lightness keeps operator fatigue to a minimum and makes it popularwith sprayers.

Nylon Air & Fluid Hose

Concentric seamless extruded construction and can bemade in many different colours for easy identification.Translucent, clear white (actually slightly cream colour) isoften used due to the ability to see liquids moving throughthe hose interior. This is durable, lightweight and flexiblealthough prone to kinking when bent in tight radii. Typically used on automatic spraying


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machines, where the fluid or air has to be fed to spray guns which are often in constant rapidmotion. Unaffected by most paints and solvents, Nylon hose can also double as fluid hose,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 alsorecommended for use with automatic and electrostatic sprayequipment. Suitable for conveying most gasses, paints andsolvents and can be used for water based materials. It isdurable and slightly more flexible than nylon hose, althoughstill prone to kinking in tight radii. Concentric seamless construction and also available invarious colours.

Air Hose Pressure LossThis 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 orpipe it rubs against the walls, losing energy and pressure as it goes. The table belowindicates just how much pressure drop can be expected at different pressures with hoses ofvarying length and internal diameters. At low pressures and short lengths of hose this drop isnot particularly significant, but as the pressure increases and hose lengthened, the pressuredrop rapidly becomes very large and must be compensated for. Far too often a tool or gun isblamed for malfunctioning when the real cause is an inadequate supply of compressed air ormaterial resulting from using too small inside diameter hose.

Hose outlet / Gun Handle Inlet Pressure

Air HoseInternal

Diameter

RegulatorPressure

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)










10 mm (3/8) 5 bar (75 psi) 3.4 bar (50 psi) 3.3 bar (48 psi) 3.1 bar (45 psi)10 mm (3/8) 6 bar (90 psi) 4.3 bar (62 psi) 4.1 bar (60 psi) 3.8 bar (55 psi)

Above data compiled using DeVilbiss DVFR-4 Regulator, H-1975, H-1921 and H-1958 rubber hose fitted withre-usable hose fittings, MPV-10 male and MPV-424 female Q/D connectors, GFHV-510 with 153 air cap. Inletpressure 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 highvolumes of air used and the high-pressure drops generated. With a hose length of 7 metres (23 ft) or greater10 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 beexperienced when the gun is triggered.

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

upon the materials and quality of manufacture. Therefore the hose length, inside diameterand quality must be considered before purchase and use for a particular job.


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Hose ConnectionsThere are several types of f lexible hose end connector available today.

Non-reusable Crimp style Non-reusable Oetiker clip typeRe-usable Jubilee clip type Re-usable ferrule type

In all cases the correct sized connectorand clip/crimp fitting must be used forthe hose selected. Failure to do so willnot only cause a connection that willnot equal the pressure rating of thehose but will also be a safety hazard,endangering sprayers during use.

The Crimp, Jubilee and Oetiker typesare cheaper to purchase but tend to bedamaged more easily, and need

replacing more often, than the moreexpensive re-usable versions. Inaddition, re-usable connectors,because they are made for a specific

size hose and type, will be designed to give the maximum airflow and minimum pressure losspossible. All too commonly, through lack of range available or lack of knowledge of thepurchaser, the wrong connector of the other styles are used, creating problems and airstarvation.

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 usedon Gun

U.K. USA Germany France BeNeLux MiddleEast

Scandanavia

FluidConnector

3/8BSP (M)

3/8NPS (M)

3/8BSP (M)

3/8BSP (M)

3/8BSP (M)

3/8NPS (M)

3/8NPS (M)

Air Connector 1/4BSP (M)

1/4NPS (M)

1/4BSP (M)

1/4BSP (M)

1/4BSP (M)

1/4NPS (M)

1/4NPS (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/Ds)

There are many types of Q/D connector available frommany different sources. The particular manufacturer of yourconnectors is not as important as their design. Q/Ds withsmall central holes (4 mm dia or less) can create severepressure loss. By using Q/Ds with 5mm holes or largerthese losses will be minimised, allowing the air tools tohave sufficient energy to work correctly. Both the DeVilbissMPV and PA Series connectors have this size orif ice, plusthe MPV Series are a European standard external profile -available and used on spray equipment all over Europe.


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Hose Care, Storage & InspectionThe hose has been designed to minimise the effects of cutting,abrasion, pulling and kinking. Nevertheless, precautions shouldbe taken when using the hose. It must be used at or below thespecified working pressure, and changes in pressure should bemade gradually to eliminate excessive surging. It should not bemishandled by kinking or running equipment over it, nor draggedover abrasive surfaces. By handling the hose properly you canextend its working life. Inspect it periodically for worn covers thatexpose the reinforcement, expanded areas in the hose, blistersin the cover and softening and compressed areas caused bykinks. If these problems are found on high-pressure airless hose. The hose must bereplaced to avoid possible hazards. However standard pressure hose can be repaired bycutting out the problem areas and installing splicers or connections. Hose that appears to besoftened by exposure to solvents, chemicals and/or heat may not be suitable for its specificuse. Hose connectors should be periodically inspected to ensure that they are secure to thehose and that they have not caused cuts or damage to the hose. Threads should be checked

for damage or contamination or diff iculties will be found attaching them to the equipment..Q/D male stems should fit securely in their female connectors and lock in place. Hosesshould be stored un-pressurised in flat coils, in a cool and dry area. Avoid tying hose withwire.

10. Equipment Air ConsumptionBelow 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 arethe equivalent air compressor sizes necessary to supply just that type of equipment. Thepower requirement can sometimes be surprisingly large! The above HPs 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 evenlarger!

Typical Air Consumption Approx. Compressor PowerNeeded

Tool l/min cfm kW HPDA Sander 425 15 2.5 3.3Air Duster 480 17 2.8 3.8

Polisher 480-708 17-25 2.8-4.2 3.8-5.6Shot Blaster 2280 80.5 13.3 17.9

DeV. MPV Full Face Air Mask 180 6.3 1 1.4DeV. 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 1.8-5.3DeV. MP Gravity Touch-in gun 25-58 0.88-2.05 0.2-0.4 0.2-0.5DeV. 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 0.6-1.1DeV. 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 3.3-3.6DeV. EGHV Touch-in gun 122 4.3 0.75 1

DeV. FLG HVLP Low cost gun 410 14.5 2.4 3.2DeV. GTI Pressure gun 425-510 15-18 2.5-3 3.3-4

DeV. KBII Pressure Feed Cup 0 0 0 0DeV. 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


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DeVilbiss DVFR-2 Filter/Regulator/Coalescer


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Ringwood RoadBournemouth

DorsetEngland

BH11 9LHTel: 00 44 (0)1202 571111

air supply 2

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