make clean oil a necessity. The air end (i.e., the rotors and their housing) of the rotary screw compressor has
no sacrificial components such as the piston rings of the reciprocating type. Since the air end is constructed
with such high precision and tight tolerances, in most cases, the entire air end must be replaced as a unit.
Inlet filters prevent dust and other particulates from entering the compressor. All compressors,
especially rotary screw compressors, are susceptible to wear or other damage from dirt particles. A clogged
filter can cause a significant loss in compressor efficiency. To prevent damage and loss of efficiency, regular
cleaning of filter elements or replacement of throw away elements is required.
Aftercoolers are installed on the discharge line to lower the compressed air discharge
temperature and to condense water from the air. Aftercoolers are usually installed with a separator and trap
to handle the condensate.
Separators are used to remove entrained liquids from the compressed air. This is usually
accomplished by changing the direction of movement of the liquid particles so that they are removed from the
air either centrifugally or through impingement against a separator element. The most common types of
separators are impingement, centrifugal, and cyclone types. Separators should be equipped with a trap or
Traps collect liquid that has been removed from the air by separation or condensation and release it,
either automatically or through a manual valve. Traps are installed with separators, filters, aftercoolers,
receivers, and dryers. They should also be installed at the low points in distribution systems, especially on lines
passing through a cold area. An inline strainer is usually installed directly upstream of a trap to prevent
sediment or other contamination from clogging the trap.
Dryers are used when dryer air is required than can be provided by an aftercooler system. The most
common are refrigerated dryers which condense the moisture from the air by reducing the air temperature.
Deliquescent type dryers absorb moisture into a deliquescent material which must be periodically replaced.
Desiccant dryers use porous moisture adsorbing materials that hold the moisture in the pores until they are
regenerated by electric heat, air purging, or both.
Pressure Regulating Valves.
Pressure regulating valves are used to supply small volumes of air to various
pneumatic equipment at a pressure lower than the system pressure.
Pressure Relief Valves.
As a safety precaution, a pressure relief valve is required in every compressed air
system ahead of the first point that could conceivably act as an air flow restriction. This includes shutoff
valves, check valves, and even in-line filters as they could clog. Receiver tanks should also have a relief valve
installed on the tank with no restrictions between the tank and the valve. If there are no restrictions in the
discharge line between the compressor and the receiver tank, the relief valve mounted on the receiver tank is
sufficient to protect the system. The relief valve should be set to open at no higher than 10 percent above the
maximum working pressure and periodically checked for proper operation. It should be noted that pressure
regulators are not acceptable for protection against excessive system pressure as they do not vent air but
regulate pressure by restricting air flow.