Page 18 - Reciprocating Compressors Operation Maintenance

Reciprocating Compressors and Their Applications 5

ressure
Increases

Gas
Volume
Decreases

Compression

FIGURE 1 -3. Compression process reduces volume of gas and increases pressure.

results in a temperature increase. Furthermore, all the molecules have
been forced into a smaller space, which results in an increased number of
collisions on a unit area of the wall. This, together with the increased
velocity, results in increased pressure.
The compression of gases to higher pressures results in higher temper-
atures, creating problems in compressor design. All basic compressor
elements, regardless of type, have certain design-limiting operating con-
ditions. When any limitation is involved, it becomes necessary to per-
form the work in more than one step of the compression process. This is
termed multistaging and uses one basic machine element designed to
operate in series with other elements of the machine.
This limitation varies with the type of compressor, but the most impor-
tant limitations include:

1. Discharge pressure—all types.
2. Pressure rise or differential—dynamic units and most displacement
types.
3. Compression ratio—dynamic units.
4. Effect of clearance—reciprocating units (this is related to the com-
pression ratio).
5. Desirability of saving power.