|Paint Spraying - Choosing an Air Compressor
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There are many different types of air compressors. An air compressor basically compresses atmospheric air to a given pressure, the air is usually stored in a pressurised vessel, the air receiver, as the air expands it creates volume and speed which can be used to atomise paint or power air tools.
For spraying the choice of compressor will depend on the air consumption and pressure requirement of the Spray Gun, and the number of spray guns used.
For the hobbyist a complete spray system can be purchased including the spray gun, hose complete with connectors and the air compressor at economical prices.
See: Compressor Starter Kits
When selecting a spray gun separately, it will be necessary to check the average air consumption in CFM (cubic feet per minute) or L/min and working pressure in either Bar or PSI (pounds per square inch). A compressor can then be purchased ensuring the FAD (free air delivery) of the unit and the pressure is equal to or more than the air consumption of the gun, usually suction spray guns need more air than gravity ones
Choosing the right compressor for your needs and then properly setting up the system is vital. If the compressor is too small the type of gun and quality of finish can be affected. If the compressor is too large then unnecessary expense will be incurred.
Using compressed air for spray painting gives greater versatility and the extra benefit of having the ability to operate other pneumatic equipment such as tyre inflators, chipping hammers, air blow gun, impact wrenches, ratchet wrenches, etc. The first factor to choosing a compressor is which type to purchase.
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The initial choice is between a Direct Drive
(mainly for hobby & less demanding work) and a
Belt Driven Compressor
(more for workshop use).
Direct Drive compressors are of a co-axial design (motor directly coupled to the pump unit), are normally single stage and therefore the atmospheric air is compressed once. These units are inexpensive to buy and operate efficiently at lower pressures.
Belt Driven compressors operate via belts and pulleys and can be single or two-stage which will produce compressed air without working as hard as a Direct Driven compressor. These units are more efficient, run cooler and deliver a greater amount of air for the power consumed.
Belt Driven compressors are usually lubricated whereas the Direct Drive models can be both lubricated and oil free. Oil free units are very popular with the keen DIY enthusiast as these units are low maintenance and can be transported easily and cleanly (no oil spills), they also offer less contamination of the paint, when this is atomised.
Fortunately it is easy to size a compressor since they are all rated according to the air delivered (cfm or litres per minute). As a guideline a 2HP compressor will deliver about 7 cfm and a 3HP compressor will delivery around 10.5 cfm FAD.
When choosing a compressor it is important to calculate the amount of air required. A spray gun that requires 7cfm average air consumption will require a compressor of approx 2HP.
Another issue to look out for when selecting a compressor is the application. For intermittent use, for example for spraying a garden fence or kitchen cupboard a small Direct Drive compressor will be more than adequate. A project that requires a more sophisticated spray gun and heavy duty (many hours of use over several days) will require a compressor producing much greater CFM normally a Belt Driven compressor of 3HP or above.
See what other tools
you can use with your compressor
Note: HVLP Spray Guns require a lot of air, always check the air consumption.
Portable or Stationary ?
Most portable units are usually mounted on either a 25 or 50 litre tank/receiver, they come complete with regulator, outlet coupling, etc. they are usually below 3HP and are usually Direct Driven, Portable Belt Driven models are available with a 50 or 60 Lt air receiver. Static units are usually designed to be wired in and installed to a pipe work system they usually start from 3HP and the tank/receiver size can range from 100 litres to 272 litres, the regulator and other accessories need to be purchased separately.
It is also essential that the "portability" of the compressor be taken into account. If the unit is to be used primarily for spraying garden fences, inflating car tyres, infrequent use of ratchet wrenches then a portable unit (wheels and handles) should be selected. There would be no obvious reason why a large static unit would be selected unless extra expense is to be spent on hoses and hose connections
The life and efficiency of the compressor will depend on the level of maintenance that is provided. When selecting the compressor great efforts have been made to ensure the system is correct and the compressor is not being worked over and above the design capacity. However, to ensure the efficiency several simply maintenance tasks need to be done:
the air receiver: water collects at the bottom of the
tank/receiver during the compression stage and the amount can depend
on the climate. This can be done manually by opening the drain valve
located at the bottom of the receiver.
is important that regular checks are made to ensure that this
apparatus is functioning correctly:
it is important that the oil level is checked regularly and “topping
up” undertaken when necessary
intake filters need to be changed annually or when they become too
an annual service is advisable especially on the larger units. Valve
plates, gaskets and Non Return Valves (NRV) can be checked and
replaced, belt(s) for belt driven models to be tensioned or replaced.
Service work should be done by an approved engineer