What is the difference: Reciprocating vs Rotary Screw Compressors?

Reciprocating vs Rotary Screw

Reciprocating or Piston Type

Reciprocating or Piston-Type compressors pump air by action of pistons. Drawing in air on the down stroke and discharging air on its upstroke. Reciprocating compressors can be single-stage or two-stage, while two-stages of compression creates greater efficiency. These compressors are designed to run for a period, and then have down time to cool. High pressures are achievable with piston compressors because the compression cycle is positive displacement. Multiple stages allow for higher pressures to be reached. An example of this would be breathing air compressors that must recharge air tanks rated for 4500psi.

The maximum operating duty cycle on a reciprocating compressor is 70%, optimal is 50%.
The maximum operating duty cycle on an oil free reciprocating compressor is 50%, optimal is 30%.

Rotary Screw

Rotary Screw uses two helical screws that rotate with close clearances next to each other. Air travels through the grooves and is compressed as the channels volume decreases, which increases pressure. Rotary compressors have fewer moving parts and excellent cooling capabilities, meaning they can run 100% of the time without needing down time to cool. Oil is used to cool, lubricate, and seal the screws – which must be separated from the air after the compression cycle. Due to the nature of lubricating the screws, there is more oil present in the discharged air. Separation is achieved by use of an Air/Oil separator.

Average CFM per Horse Power by compressor type