Compressors : Hermetic and Semi-Hermetic Compressor

 Hermetic compressors have a welded steel shell and internal components, including a suction gas-cooled motor.

Hermetic Compressors:

• The term "hermetic" refers to an airtight container.

• Components like pistons, valves, crankshaft, and motor are enclosed in a welded shell.

• Suction vapors pass across the motor, cooling it before entering the pumping mechanism and being discharged to the condenser coil.

Semi-Hermetic Compressors:

• Semi-hermetic compressors have cast iron shells bolted together, allowing on-site repairs such as valve plate and oil changes.

• Larger repairs can be done by sending the compressor back to the factory for rebuilding.

• These compressors can be air-cooled, water-cooled, or suction gas-cooled, and they typically have an oil pump driven by the crankshaft.

Cooling Methods for Semi-Hermetic Compressors:

• Water-Cooled: Soft tubing can be coiled around the compressor to remove heat.

• Air-Cooled: Air is blown across the compressor, either by the condenser fan or a separate fan.

• Suction-Cooled: Suction vapor passes over the motor to cool it before entering the pumping mechanism.

Components of Semi-Hermetic Compressors:

• Electrical components include the motor overload and terminals.

• Mechanical components include the crankshaft, pistons, valves, head, connecting rods, and wrist pins.

• The crankshaft has a hollow center with holes for bearing lubrication.

Lubrication in Compressors:

• Proper lubrication is crucial for all load-bearing surfaces.

• The crankshaft has a hollow center for oil distribution, with an oil pump drawing oil from the crankcase to lubricate the pistons and crankshaft bearings.

• The oil drains back to the crankcase and is continuously circulated.

Oil Level Monitoring:

• The oil level should be visible in the sight glass.

• If the oil level is too high, it could indicate excessive oil or refrigerant migration.

• A low oil level means no oil will be visible in the sight glass.

• Manufacturers may specify the acceptable oil level range between one-third and two-thirds of the sight glass.