The oil is circulated in a closed loop, typically by pressure differential rather than a separate pump.
Fixed suction and discharge ports. No valves.
Zero reciprocating motion, only high speed balanced rotation.
Many screw compressor frames feature internal capacity control to as low as 10% capacity with a slide valve.
Some frames can rotate as high as 10,000 rpm with a gearbox. This displaces significantly more gas than a slower rotating alternative with an equivalent swept volume. Less iron to move more gas.
Gas and oil mixes in the compressor frame. The oil absorbs heat from the gas, allowing more ratios of compression in a single stage… No intercooler, no additional cylinders, less interconnected piping.
Disadvantages of Screw Compressors
Limited discharge pressures.
Typically limited to 375 psig (2,585 kPag), depending on manufacturer.
Inefficient in high ratio applications.
As they exceed 5 compression ratios, screw compressors consume incremementally more power for compression. The capital cost is lower than a multi-stage reciprocating compressor, but the power costs will increase.
What’s NEXT for Screw Compressors
High pressure models. Establishing runtime and familiarity with the high pressure screw compressor will bring more options to an application dominated by reciprocating packages.
Increased rotor diameters. Higher capacity means more applications suitable for a screw compressor installation.