Does Sentry use a MOP (maximum operating pressure) TEV to prevent liquid entering the compressor?
A MOP style thermal expansion valve limits the refrigerant pressure available to the evaporator. Often at startup, the process water is hot. Elevated temperatures on the process side of the evaporator elevate the temperature and pressure inside the evaporator. A MOP limits the maximum refrigerant pressure in the evaporator. As the evaporator pressure reaches the MOP set point the TEV closes, starving the evaporator thereby limiting the pressure. A Sentry TCU does not us a MOP type thermal expansion valve. Typical MOP valves have a charge in the bulb to control pressure at or less than 100 psig (7 bar). The evaporator on the TCU is controlling process water temperature at 77° F (25° C). The superheat is designed to be 12° F, implying an evaporating temperature of 65° F (18° C). Evaporating at 65° F corresponds to a R-22 pressure of 110 psig (7.5 bar). An off-the-shelf MOP will not work in our system. Instead Sentry uses a crankcase pressure regulator to limit the pressure at the suction
