Screw compressor
A screw compressor traps gas in spaces bounded by helical working elements and the housing. Their volume decreases as gas moves toward the discharge.
Guide
ContentsTwin-screw and single-screw mechanisms
A twin-screw machine uses intermeshing helical rotors. A single-screw arrangement uses a main screw with mating gate rotors. These are different constructions within the positive-displacement family. The mechanism does not, by itself, state its refrigerant, enclosure or permitted speed.
Internal volume ratio and system pressure
Internal volume ratio compares the trapped gas volume at the start of compression with its volume when the discharge port opens. It is a geometric property and differs from the system’s absolute pressure ratio. Their mismatch can increase compression losses; fixed or adjustable arrangements must be evaluated at the intended duty.
Oil and capacity control
In oil-injected designs, oil participates in lubrication, sealing and thermal management, with separation and return integrated into the system. Capacity control may use a slide valve, speed variation or both, if supported. Oil circuit requirements and minimum operating conditions remain necessary at part load.
Selection for a chiller or refrigeration plant
Compare the exact compressor map at the chosen refrigerant and operating temperatures, including part load. State whether the supply includes motor or drive, oil system, valves, sensors and controls. A bare compressor and an assembled package have different installation and quotation scopes.
Prepare a compressor request
Pressure conversion and pressure-ratio calculation · model selection unavailable
The pressure tool converts the supplied values and calculates the absolute discharge-to-suction pressure ratio. The request form records other requirements. Neither function selects a compressor, calculates capacity or confirms a refrigerant cycle, diagnosis or interchangeability.
For a technical review, identify the exact model and refrigerant, duty and rating conditions, electrical supply and control, oil, dimensions/connections, and the reason for replacement or service. Missing information remains unknown.
Selection / replacement · Service
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Absolute pressures and pressure ratio
Use suction and discharge pressures for the same stated operating condition and compatible measurement definitions. This is a pressure calculation; it does not check whether a compressor can operate at those pressures.
Method: 1 bar = 100 kPa; 1 MPa = 1000 kPa. Convert each input to kPa. For gauge pressure, p(abs) = p(gauge) + p(atm). For absolute pressure, use the entered value directly. r = p(discharge, abs) / p(suction, abs); r has no unit.
Both absolute pressures must be positive. Enter a positive absolute atmospheric pressure whenever either input is gauge. A negative gauge reading is allowed if its absolute pressure remains positive. Atmosphere is never assumed.
Example: suction 2 bar absolute and discharge 8 bar absolute give 200 kPa, 800 kPa and r = 4. The same result follows from 1 bar gauge and 7 bar gauge with an explicitly supplied atmosphere of 1 bar absolute.
The calculation does not provide cooling capacity, power, discharge temperature, an operating envelope, refrigerant/oil compatibility, diagnosis or a replacement model. Pressure sources, measurement uncertainty, operating stability and model limits remain unverified. Displayed results are rounded; extreme values outside finite numeric precision are rejected.