Unloader and pressure switch control. Engine-drive compressors have unloaders which
automatically disconnect the compressing cylinders from the air storage tank and allow the engine to continue to run at an
idling speed until the tank pressure decreases to a preset minimum pressure. When the tank pressure reaches its preset
minimum, the unloader valve automatically advances the engine throttle, opens the valves, and causes the pressure to be
built up again. Electric motor-driven compressors have a pressure switch which shuts off the motor when a
predetermined pressure has been established and restarts it when the pressure has fallen to a predetermined point.
Horizontal and vertical tanks. Normally, compressor tanks are mounted in a horizontal position,
serving as a base for the compressing unit. Where space is limited, or where ground clearance ora corner installation is
important, tanks can be mounted in a vertical position.
Air or water cooled compressors. The physical process of compression produces heat, and for that
reason it is particularly important that air compressors be adequately cooled. Most compressors intended for use with
spray painting equipment are air cooled. To accomplish this, the exterior surfaces of cylinders, intercoolers, and after-
coolers are greatly increased in area by the use of fins. Increased surface area allows heat to be radiated more rapidly.
Larger compressors, when used continuously, cannot be adequately cooled by air. Such compressors use a water
cooling system consisting of a radiator, pump, fan, and water jackets built around the cylinders and are similar to those of
Truck outfits. Air compressors, usually with gasoline engines for power, are often mounted on light,
easily moved trucks. These portable units are ideal where painting is to be done at various locations.
Inspection and lubrication of compressors.
Do not make adjustments or repairs to gasoline engines unless qualified to do so.
Gasoline-driven air compressors are furnished with engines manufactured by many different companies. Generally
speaking, they are of low horsepower and simple construction. For instructions on how to lubricate and adjust, refer to
pertinent Technical Manuals. Adjustments to the carburetor, gasoline lines, and ignition systems should not be made in or
near the paint shop. While the maintenance and repair of gasoline engines is not the responsibility of the painter, he
should be sufficiently familiar with them to correct any minor stoppages caused by improper adjustment. Most gasoline
engines used on compressors are adjusted at the factory to run at a constant speed and no throttle adjustments should be
Electric motor. For lubrication of electric motors, refer to pertinent Technical Manuals. The
adjustment of electric motors, even of a minor nature, is not the responsibility of the painter and should be undertaken
only by qualified personnel. It is, however, the reponsibility of the operator to see that the electric motor on his
compressor is not damaged through improper use. All electric motors, when overloaded, overheat, usually very rapidly. If
this condition is allowed to persist for even a brief interval, the insulation on the winding may burn away. The use of fuses
and circuit breakers is intended to prevent this, and the operator should familiarize himself with them. In no event should
fuses be shorted or circuit breakers tied down.
Care and preservation. For care and preservation of compressors, refer to pertinent Technical
Operation of compressors.
Installation. Proper operation of a compressor system depends to a great extent on the correct initial
installation of the equipment. The following points are important to proper installation: electrical wiring, whether for a
permanent or portable installation, presents a fire hazard at all times, and should be installed and inspected by a
competent electrician, as fire in a paint shop is devastating and almost impossible to control.