Reciprocating compressors pistons

In much the same manner as pumps, compressors are classified as one of two general classes positive displacement or dynamic (see Figure 3-68) [23]. These two general classes of compressors are the same as that for pumps. The positive displacement class of compressors is an intermittent flow device, which is usually a reciprocating piston compressor or a rotary compressor (e.g., sliding vane, screws, etc.). The dynamic class of compressor is a continuous flow device, which is usually an axial-flow or centrifugal compressor (or mix of the two). 

Figure 3-71. Single-acting (trunk-type) reciprocating piston compressor [23].

Most reciprocating compressors have inlet and outlet valves (on the piston heads) that are actuated by a pressure difference. These are called self acting valves. There are some larger multistage reciprocating piston compressors that do have camshaft-controlled valves with rotary slide valves. 

The main disadvantages to multistage reciprocating piston compressors is that they cannot be practically constructed in machines capable of volumetric flowrates much beyond 1,000 actual cfm. Also, the higher-capacity compressors are rather large and bulky and generally require more maintenance than similar capacity rotary compressors. 

The first three factors are present in compressors, but they are small and on the whole can be neglected. The clearance volume problem, however, is unique to reciprocating piston compressors. The volumetric efficiency e estimates the effect of clearance. The volumetric efficiency can be approximated as... 

Figure 3-73. Volumetric efficiency for reciprocating piston compressors (with ciearance) [4].

Real surfaces, radiation 441,443 RbavblI.. B. N, 274, 302, 3 1 Reboilers 494, 495, 496 Reciprocal rule 448 Reciprocating piston compressor 347... 

The performance of reciprocating (piston) compressors with large valve area, or where valve losses are evaluated, is considered as close to... 

Reciprocating piston compressors. Compression ratios are 1.2 to 6 select to keep outlet temperature <150°C. Efficiencies for reciprocating compressors are 65% for compression ratio 1.5 75% compression ratio 2, and 80% to 85% for compression ratios 3 to 6. Power 70 to 1200 kW/mVs. 

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