Positive displacement refrigeration compressor

Technical information Chillers Positive Displacement Compressors

Piston Compressors

Water chillers up to 100 tons capacity, as a rule, use one or more of three-dimensional type of reciprocating compressors.

Piston compressor uses the pistons in the cylinders to compress the refrigerant gas. Basically, it works like 2-stroke engines except for the fact that the compressor consumes shaft energy than it produces. The refrigerant gas enters the cylinder through the inlet valve down stroke. Intake valve closes as the piston starts up the compression stroke, and when the pressure is high enough to overcome the resistance of the spring, the discharge valve opens and gas from the cylinder. The discharge valve closes as the piston reaches top dead center, and the cycle is repeated as the piston starts down with another intake stroke. The pistons are connected displacement vane crankshaft through the connecting rods. Compressor motor rotates the crankshaft, and this rotation is converted to reciprocating motion of the pistons.

Control piston compressor refrigeration system is quite simple. At the compressor, the head pressure regulator senses of the compressor discharge pressure and opens higher and higher, on the compressor, if the pressure rises above a preset value.

The unloader a valve that relieves the refrigerant gas with high-pressure compressor discharge in low-pressure suction side, thus effectively increasing the inlet pressure and the decrease in the net differential pressure required for the compressor. High-pressure setpoint is based on the condensation of requirements and, as a rule, pressure corresponds to approximately 105F refrigerant (R-22 or R-410A).

Temperature sensor is located on the suction line at the evaporator output modulates the expansion valve to maintain the set-point. Thus, as the load on the evaporator change, the flow rate through the expansion valve changed accordingly. The expansion valve, sensor detects a high temperature (i.e., overheating)if the flow rate is too low and low temperature (i.e., hypothermia), if the speed is too high. This is the set-point temperature, typically 40F for comfort applications.

Reciprocating chillers water more than 20 tons capacity almost always several compressor units. When you select multiple chiller compressor, it is important that the compressors independent refrigerant circuits, so that if one pump fails, the remaining one(s) may continue to operate. Some lower-cost units in all compressors operating in parallel on a single refrigerant circuit...

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