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Understanding Maximum Operating Pressure TXVs
2017/08/09
August 7, 2017
Thermostatic expansion valves (TXVs) come in many different shapes and sizes. Although they all are designed to control the superheat value of the refrigerant leaving an evaporator, there are some differences among TXVs that either enhance their operation or slightly change how they operate. One of these differences is in the design of the valve’s power element. There are different types of power assemblies that can be used on the body of an expansion valve. One of these types is the maximum operating pressure (MOP) power element.
 
An expansion valve with an MOP-type power element is designed to limit the evaporator pressure from rising above a predetermined value. Above its MOP setting, the valve will essentially close, preventing the evaporator pressure from rising higher. This prevents a compressor’s motor from overloading if the suction pressure reaches a value beyond its designed operating parameters. This type of valve tends to serve the same basic function as a crankcase pressure regulator (CPR). Because of this, it is not normally recommended that an MOP-type expansion valve and a CPR be used on the same system as they may fight each other for control of the suction pressure.
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