Trane TRG-TRC004-EN manual OLQGHU8QORDGHUV, Cylinder Unloaders

period two

Compressor Capacity Control

notes

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Cylinder Unloaders

Most large reciprocating compressors (above 10 tons [35 kW]) are fitted with cylinder unloaders that are used to match the compressor’s refrigerant- pumping capacity with the falling evaporator load, by progressively deactivating piston–cylinder pairs.

The cylinder unloader shown in this example reciprocating compressor uses an electrically-actuated unloader valve to close the suction passage to the cylinder that is being unloaded.

In response to a decreasing load, an electronic controller sends a signal to open a solenoid valve. This solenoid valve diverts pressurized refrigerant vapor from the compressor discharge to the top of the unloader valve, causing the unloader valve to close and shut off the flow of refrigerant vapor into the cylinder. Even though the piston continues to travel back and forth inside this cylinder, it is no longer performing compression since it cannot take in any refrigerant vapor.

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