Screw compressor
Also known as: helical compressor, twin-screw compressor
Short definitionA high-capacity compressor that compresses vapour continuously between two meshing helical rotors. It is the machine of central systems and large stores.
As the male and female rotors turn together, the volume between them narrows from the suction side to the discharge side. The vapour is compressed in a smooth, continuous flow. There are no valves and vibration is low. Capacity runs from 50 kW to several megawatts. A slide valve adjusts the load steplessly between 10% and 100%, so the machine stays efficient under varying load.
It is used in large frozen stores, blast freezing tunnels and ammonia plants. An economiser port gives good single-stage efficiency at low evaporating temperatures. Oil seals and cools the rotors, so a large oil separator and an oil cooler are essential. The investment is high and maintenance calls for a specialist. For small and medium rooms, a condensing unit with a reciprocating or scroll compressor is the better choice.