The controller suction pressure (SPR) is a safety device that keeps the pressure at the compressor inlet below high-limit set point. He supports this limit regardless of how high the evaporator pressure increases as the result of increase of the load. For this reason, the controller suction pressure is often called the crankcase pressure regulator or suction pressure hold-back valve. SPRs are used to protect the compressor motor against overloads during periods of higher than normal evaporator loads. They are recommended for use in any application where the system is subjected to a long work under manometric suction pressure, high starting loads, spikes suction pressure, high suction pressure produced by hot gas or reverse cycle defrost (heat pump) operations.
Suction valves pressure control modulating devices that react to changes in their outlet pressure. Port of entry in the SPR is passed to the suction line when the output port is transferred to the valve on the compressor suction. The pressure in the crankcase creates a force to die on the bottom of the plug (seat disc).
This force is always tiying to close the valve. It is opposed die force generated by the set point adjustment spring. Therefore, increasing specified spring force also increases the operating pressure of the valve and the maximum allowable pressure in the crankcase. Inlet pressure (suction pressure) is also affecting the bottom side of the bellows and the top of the valve disc plug. Since the effective size of the bellows is equal to the effective area fork influence of input offset and does not affect the valve's operation.
Until the pressure in the crankcase of the compressor remains less than the maximum pressure setpoint high limit, the valve remains open. At full load, the valve will be 100% open, but if the pressure in the crankcase of the compressor increases above the SPR, set value, the valve begins to modulate in direction closed. This action, reduces the flow of refrigerant in the compressor, limit the pressure in the crankcase. As the outlet pressure drops below the maximum limit specified value, the valve is opened, increasing the flow of refrigerant in the compressor. The controller suction pressure is installed near the compressor, downstream from all the other controls in the suction line. As evaporator pressure regulators, suction pressure available in pilot configurations for large-capacity storage systems...
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