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Scroll compressor

A scroll compressor compresses gas in pockets between two interleaved spirals. It combines a positive-displacement principle with orbital motion.

Guide

Contents

Fixed and orbiting scrolls

In the usual arrangement one scroll is fixed and the other orbits without rotating about its own centre. Gas enters outer pockets, moves inward as they shrink and exits near the centre. Multiple pockets can be at different compression stages at the same instant. This does not make the machine a multistage compressor in the circuit-design sense.

Air-conditioning and heat-pump duties

Scroll machines serve air-conditioning, heat-pump and refrigeration duties, with model-specific refrigerants and temperature ranges. Some constructions support vapour injection at an intermediate point in compression. Such an injection connection and its auxiliary circuit must be part of the approved design; they are not a universal scroll feature.

Speed and unloading

Scroll capacity can be controlled through on/off operation, an approved variable-speed drive or a supported unloading method. A mechanically modulated scroll is not necessarily variable-speed. Compare its minimum stable output, operating map and system controls; do not infer efficiency from the control label alone.

Model and circuit compatibility

Verify refrigerant, lubricant, drive, rotation requirements, protective devices and the operating envelope. A welded shell usually means the internal mechanism is replaced as an assembly. Before replacement, identify liquid return, overheating, oil-return or electrical conditions that could repeat the failure.

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

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.