The air supply to the spray gun must be entirely free of water  or oil in order to produce the optimum results in the finished  product. Water traps, as well as suitable filters to remove any  trace of oil, must be incorporated in the air pressure supply  line. These filters and traps must be serviced on a regular basis. A paint booth may be a small room in which components  of an aircraft are painted, or it can be an aircraft hangar big  enough to house the largest aircraft. Whichever it is, the  location must be able to protect the components or aircraft  from the elements. Ideally, it would have temperature and  humidity controls; but, in all cases, the booth or hangar must  have good lighting, proper ventilation, and be dust free.  A simple paint booth can be constructed for a small aircraft  by making a frame out of wood or polyvinyl chloride (PVC)  pipe. It needs to be large enough to allow room to walk around  and maneuver the spray gun. The top and sides can be covered  with plastic sheeting stapled or taped to the frame. An exhaust  fan can be added to one end with a large air-conditioning  filter placed on the opposite end to filter incoming air. Lights  should be large enough to be set up outside of the spray booth  and shine through the sheeting or plastic windows. The ideal  amount of light would be enough to produce a glare off of  all the surfaces to be sprayed. This type of temporary booth  can be set up in a hangar, a garage, or outside on a ramp, if  the weather and temperature are favorable. Normally, Environmental Protection Agency (EPA)  regulations do not apply to a person painting one airplane.  However, anyone planning to paint an aircraft should be  aware that local clean air regulations may be applicable to an  airplane painting project. When planning to paint an aircraft  at an airport, it would be a good idea to check with the local  airport authority before starting.  The air supply for paint spraying using a conventional siphon  feed spray gun should come from an air compressor with a  storage tank big enough to provide an uninterrupted supply  of air with at least 90 pounds per square inch (psi) providing  10 cubic feet per minute (CFM) of air to the spray gun.  The compressor needs to be equipped with a regulator, water  trap, air hose, and an adequate filter system to ensure that  clean, dry, oil-free air is delivered to the spray gun.  If using one of the newer high-volume low-pressure (HVLP)  spray guns and using a conventional compressor, it is better  to use a two stage compressor of at least a 5 horsepower (hp)  that operates at 90 psi and provides 20 CFM to the gun. The  key to the operation of the newer HVLP spray guns is the  air volume, not the pressure.  If purchasing a new complete HVLP system, the air supply  is from a turbine compressor. An HVLP turbine has a series  of fans, or stages, that move a lot of air at low pressure.  The more stages provide greater air output (rated in CFM)  that means better atomization of the coating being sprayed.  The intake air is also the cooling air for the motor. This air  is filtered from dirt and dust particles prior to entering the  turbine. Some turbines also have a second filter for the air  supply to the spray gun. The turbine does not produce oil  or water to contaminate the air supply, but the air supply  from the turbine heats up, causing the paint to dry faster, so  you may need an additional length of hose to reduce the air  temperature at the spray gun.  Piston–type compressors are available with one-stage and  multiple-stage compressors, various size motors, and various  size supply tanks. The main requirement for painting is to  ensure the spray gun has a continuous supplied volume of  air. Piston-type compressors compress air and deliver it to  a storage tank. Most compressors provide over 100 psi, but  only the larger ones provide the volume of air needed for an  uninterrupted supply to the gun. The multistage compressor  is a good choice for a shop when a large volume of air is  needed for pneumatic tools. When in doubt about the size of  the compressor, compare the manufacturer’s specifications  and get the largest one possible.  [Figure 8-1] Figure 8-1.  Standard air compressor. Finishing Equipment Paint Booth Spray Equipment Air Compressors Air Supply 8-6