Air Compressor Terms

Different Drive Options and Duty Cycles as well as cooling methods determine what air compressor you need

Drive method is probably the simplest method of differentiating compressors.

The compressor, whether reciprocating or rotary, can be v-belt driven, direct coupled, or either of the above accompanied by a variable frequency drive. The simple v-belt drive is most commonly seen on the air cooled reciprocating compressor, and smaller rotary screw compressors. V-belt drives provide for versatility in selecting optimum speeds for the desired flow and pressure. Direct drive (coupled) compressors require that the air end be constructed to maximize the flow (CFM) for a given horsepower motor, or use internal gears to adjust the speed of the compressor to achieve this maximum flow.

Variable speed (frequency) drives adjust the speed for optimum flow and pressure by adjusting the frequency of the incoming power to the compressor.

The final method of compressor differentiation is by duty cycle. This determines the amount of time the compressor can safely run without shutting down for cooling.

Small air-cooled reciprocating air compressors generally are allowed to run 75% of the time and be idle for 25% of the time. This allows the components to cool between cycles. Rotary compressors and water cooled reciprocating compressors can run continuously 24/7, shutting down only for periodic maintenance.

Centrifugal compressors are also designed to run continuously 24/7.

Finally, cooling method be a determinant of compressor type. This is simple, as there are only two. Cooling can be either air-cooled or water-cooled. Rotary screw compressors, if air cooled, use a radiator-style cooler (heat exchanger) for both oil cooling and after-cooling. If water cooled, shell and tube type heat exchangers are typically used. Plate-fin coolers can also be used.

Air-cooled reciprocating air compressors will typically use a finned tube intercooler and the same for after-cooler. Some will use a radiator type for after cooler. Water cooled reciprocating compressors will typically use shell and tube heat exchangers for both intercooling and for the after-cooler.

Centrifugal compressors will generally be water cooled, and use shell and tube type coolers.

See the first article in this series here

See the second article in this series here

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