Compressor: hermetic, semi-hermetic and open-drive
Enclosure classification describes the relationship between the compressor, motor and refrigerant boundary. It is independent of the gas-compression mechanism.
Guide
ContentsHermetic construction
The motor and compression mechanism share a sealed housing, commonly welded. There is no external rotating shaft penetration. Internal field repair is generally not provided; service decisions concern the complete assembly and its external components. Hermetic does not mean the complete refrigeration circuit needs no inspection.
Semi-hermetic construction
The motor is inside the refrigerant enclosure, but bolted covers allow access to defined internal components. Gaskets and seals make the assembled joints refrigerant-tight. Access makes some repairs possible; the model’s procedures, parts and measured condition determine whether a repair is justified.
Open-drive construction
A separate motor or other driver transmits torque through a shaft that crosses the refrigerant boundary. The shaft seal, alignment and coupling are part of the installation. Open describes the drive arrangement; it does not mean the refrigerant chamber is open to the atmosphere.
What the enclosure does and does not tell you
Enclosure helps determine internal service access and drive integration. It does not prove refrigerant compatibility, capacity, efficiency or lifetime. A same-type enclosure is insufficient for replacement: compare mechanism, motor, electrical supply, control, oil, mounting and documented operating limits.
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.