Page 122 - Air and Gas Drilling Manual

4-8 Air and Gas Drilling Manual
non-liquid lubricated compressors. These compressors have piston rings and wear
bands around the periphery of each piston. These wear bands are made of special
wear-resistant dry lubricating materials such as polytetrafluorethylene. Trunk type
non-lubricated compressors have dry crankcases with permanently lubricated
bearings. Crosshead type compressors usually have lengthened piston rods to ensure
that no oil wet parts enter the compression space [1, 7].

Figure 4-7: Single-acting (trunk type) reciprocating piston compressor [1].

Figure 4-8: Double-acting (crosshead type) reciprocating piston compressor [1].
Most reciprocating compressors have inlet and outlet valves (on the piston
heads) that are actuated by a pressure differential. These are called self-acting valves.
There are some larger multistage reciprocating piston compressors that do have
camshaft-controlled valves with rotary slide valves.