Centrifugal pumps and compressors are both rotating equipment devices. Each is a machine that imparts kinetic energy to the fluid to create pressure and move liquids, gases, and other process materials. So what are the differences between pumps and compressors?
The main differences are intimately connected with the properties of the process fluid medium being acted upon. Both centrifugal pumps and compressors are a sub-class of rotodynamic turbomachinery, devices that kinetically transfer energy from a spinning rotor to a fluid.
A centrifugal pump works on liquids or mixtures of liquids and gases. Its usual function is to develop pressure against a connected system to move a relatively incompressible liquid medium from point A to point B, or circulate it in a confined system.
A centrifugal compressor works on gaseous fluids and achieves a substantial volume reduction and energy storage in the medium. The compressed medium may then be stored or conveyed from point A to point B.
For the sake of comparison, consider two of the most common fluids. Air, near sea level at a temperature of 20 °C (68 °F) and 50% humidity, has a density of 1.195 kg/m^3 (0.0746 lb/ft^3). Water, at the same temperature, has a density of 998 kg/m^3 (62.3 lb/ft^3). At these conditions, water is 835 times more dense than air.
Of course, the various liquids and gases handled by pumps and compressors will have range of densities, but the nearly two orders of magnitude difference is typical. Gases are highly compressible and liquids are relatively incompressible. These significant differences in fluid properties suggest that there are significant differences in the designs of machines that handle them. Indeed there are. Table 1 provides a summary comparison of the important differences and similarities between these two turbomachine types.
On the surface, the centrifugal pump and compressor appear to be similar pieces of equipment. They both achieve a transfer of work by kinetic action of one or more rotating impellers. Other design elements may also “similar.” But below the superficial similarties, there are significant design differences between these two turbomachine types.