## DYNAMIC COMPRESSORS – RPM AND HORSEPOWER

RPM AND HORSEPOWER

For all rotating machines, RPM is an important parameter. The impeller of a centrifugal compressor has to rotate (revolve) to move the gas.

As the RPM of the impeller increases, the velocity of the gas also increases.

Gas velocity is proportional to the RPM of the impeller, as shown below.

For any given RPM, a set amount of work in foot pounds or kilogram meter is done on the gas per unit weight. Since this velocity is converted into head or pressure, for a constant RPM, the head developed is fairly constant.

Whether the gas is heavier or lighter, the work done per pound of gas is the same for the same RPM.

At a given RPM, the ACFM of gas the compressor compresses will be constant. But the weight of the gas compressed will be more, in the case of a heavier gas. When more weight of gas is compressed, the work done on a heavier gas will be more.

When the rate of work done on a gas increases, the horsepower Ârequired to compress a heavier gas also increases.