Classification

Reciprocating compressors can be classified into several types. One type is the trunk or automotive piston type (see Figure 3-2). The piston is connected to a connecting rod, which is in turn connected directly to the crankshaft. This type of compressor has a single-acting cylinder and is limited to refrigeration service and to smaller air compressors. Most of the smaller packaged refrigeration system compressors are of this type. The compressors may be single or multistage. Approximate capacity is 50 tons in water-chilled refrigeration service and 75 scfm in air service.

Figure 3-2. Trunk-piston type two-stage compressor with fins for air cooling

(Courtesy of Ingersoll-Rand)

Figure 3-2. Trunk-piston type two-stage compressor with fins for air cooling

(Courtesy of Ingersoll-Rand)

The more common type of compressor used in process service is the crosshead type, as shown in Figure 3-3. The piston is driven by a fixed piston rod that passes through a stuffing or packing box and is connected to a crosshead. The crosshead, in turn, is connected to the crankshaft by a connecting rod. In this design, the cylinder is isolated from the crankcase by a distance piece. A variable length or double distance piece is used to keep crankcase lubrication from being exposed to the process gas. This design has obvious advantages for hazardous material. The cylinder can be either single- or double-acting. The double-acting construction uses both sides of the piston and compresses on both strokes of the piston during one revolution. Except for very small compressors, most reciprocating compressors furnished to the process industry use the double-acting configuration.

Figure 3-3. Typical multistage crosshead type compressor, (Courtesy ofNuovo Pignone)
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