Reciprocating Compressor M Series
1-11
1.4.5 Automatic Control and Protection Equipment M compressor
Overview/Function/Purpose
z Oil pressure failure protection equipment (OP)
When the oil pressure in compressor (Gauge pressure minus crank case pressure) drops because of
deficiency in the refrigeration oil, clogging of filter, or interfusion of refrigerant, it automatically shuts
off the motor circuit and stops the operation of compressor.
This intended to prevent damage to the compressor from abnormal friction. Can also cause the
unloader mechanism to malfunction
z High pressure protection equipment (HP)
When the discharge pressure on compressor becomes abnormally high. HP switch shuts off the motor
circuit automatically to stop the operation of compressor.
Prevents system ruptures and refrigerant leaks.
z Control of the compressor capacity: Low pressure control equipment (LP)
The number of capacity control steps in a compressor are determined by the number of cylinders.
Generally two cylinders are considered one bank. Therefore, capacity control of four steps is available
for eight cylinders, three steps for six cylinders, and two steps for four cylinders. Capacity control is
performed by detecting suction pressure a low pressure control switch is used. It automatically controls
opening/closing of the solenoid valve connected to the unloader piston in the capacity control
mechanism of compressor.
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