Figure 7-43.Air compressor.

Like hydraulic filters, air filters have a removable element and a built-in relief valve. The relief valve is designed to open and bypass the air supply around the filter element should the element become clogged. Some air filters are equipped with the micronic-type element, which must be replaced periodically. Others have the screen mesh type, which requires periodic cleaning. The latter type may be reinstalled after cleaning and drying.

AIR PRESSURE REGULATORS. A pressure regulator is generally located in the line between the engine compressor and the pneumatic system compressor; however, it may be incorporated within the system moisture separator. Its purpose is to regulate the pressure of the supply air before it enters the system compressor. The pressure regulator maintains a stable outlet pressure regardless of the inlet pressure.

MOISTURE SEPARATORS. The moisture separator in a pneumatic system is always located downstream of the compressor. Its purpose is to remove any moisture caused by the compressor. A complete moisture separator consists of a reservoir, a pressure switch, a dump valve, and a check valve, and it may also include a regulator and a relief valve. The dump valve is energized and de-energized by the pressure switch. When de-energized, it completely purges the separator reservoir and lines up to the compressor. The check valve protects the system against pressure loss during the dumping cycle and prevents reverse flow through the separator.

RELIEF VALVES. A relief valve is incorporated in a pneumatic system to protect the system from overpressurization. Overpressurization is generally caused by thermal expansion (heat). Relief valves are generally adjusted to open and close at pressures slightly above normal system operating pressure. For example, in a system designed to operate at 3,000 psi, the relief valve might be set to open at 3,750 psi and reseat at 3,250 psi.

CHEMICAL DRIERS. Chemical driers are incorporated at various locations in a pneumatic system. Their purpose is to absorb any moisture that may collect in the lines and other parts of the system. Each drier contains a cartridge, which should be blue in color. If otherwise noted, the cartridge is to be considered contaminated with moisture and should be replaced.

STORAGE CYLINDERS. Pneumatic storage cylinders (bottles) are made of steel and maybe either

Figure 7-44.Air cylinder.

cylindrical or spherical in shape. Both types of cylinders are made up of two main partsthe container itself and a manifold assembly. The container serves as a trap for moisture, as well as an air storage space. The manifold assembly is made up of the "in" and "outlet" ports and a moisture drain fitting. See figure 7-44.

Cooling of the high-pressure air in the storage cylinders will cause some condensation to collect in them. To ensure positive operation of systems, storage cylinders must be purged of moisture periodically. This is accomplished by slightly cracking the moisture drain fitting, located on the cylinder manifold.

Some aircraft have a pneumatic system that will maintain the required pressure in these bottles in flight. However, most of these pneumatic systems require servicing on the ground with an external source of high-pressure air or nitrogen prior to each flight.

Air storage bottles are serviced in the same manner as accumulators. Most air bottles have an air filler valve and a pressure gauge. These systems generally require higher servicing pressure than accumulators.

Since gases expand with heat and contract when cooled, air storage bottles are usually filled to a given pressure at ambient temperature. A graph similar to that shown in figure 7-45 is usually mounted on a

Figure 7-45.Pneumatic storage cylinder inflation chart.

plate or decal on or near the bottle or air filler valve. If the instruction plate is missing or not readable, the information may be found in the General Information and Servicing section of the applicable MIM.

Pressure should be added to air storage bottles slowly in order not to build up heat from rapid transfer. You should take care to ensure that air storage bottles are not overinflated.

NOTE: Although the following References were current when this TRAMAN was published, their continued currency cannot be assured. Therefore, you need to be sure that you are studying the latest revision.

Aviation Hydraulics Manual, NAVAIR 01-1A-17, Commander, Naval Air Systems Command, Washington, D.C., 1 April 1978, Change 2, 1 December 1986, RAC 4, 15 August 1989, Sections I, VII, VIII, and XI.

Fluid Power, NAVEDTRA 12964, Naval Education and Training Program Management Support Activity, Pensacola, Fla., JuIy 1990, Chapters 1, 4, 9, and 11.