Marine Engineering Refresher.
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Sunday, June 16, 2013
UNLOADING MECHANISM OF REFRIGERATION COMPRESSOR (pics included)
UNLOADING MECHANISM OF REFRIGERATION COMPRESSOR!
When the compressor is not in operation, the unloader mechanism is in the unloaded position. The mechanism is operated by oil pressure from the capacity control valve. The oil pressure pushes the unloader spring against the unloader piston.
This action moves the unloader rod to the left, thereby rotating the cam rings. As the cam rings are rotated, the lifting pins are forced upward, raising the suction valve off its seat. The suction valve is held in this position until the compressor is started and oil pressure of approximately 30 psi is reached. At that time, the oil pressure from the capacity control valve pushes the unloader piston back to the right against the unloader spring. The motion transmitted through the pushrod, it rotates the cam ring. This lowers the lifting pins and allows the suction valve to close or operate normally and the cylinder to become loaded. On most compressors the unloader is connected to the cylinders in pairs.