A mechanical shaft seal is necessary on a...

• A. Hermetic compressor
• B. Open drive compressor
• C. Scroll compressor
• D. Rotary vane compressor

Answer: (B)

Open drive designs place the motor and compressor on opposite sides with a shaft passing through the compressor housing. A mechanical shaft seal is needed there to prevent refrigerant and oil from leaking along the shaft and to keep contaminants out while the shaft is rotating. In contrast, hermetic or semi-hermetic designs enclose the motor and compressor in a single sealed enclosure, so there is no external shaft to seal; scroll and rotary vane units are typically hermetic or semi-hermetic, so they don’t rely on a shaft seal. That’s why an open drive compressor requires a mechanical shaft seal.