In some ships, several refrigerated spaces of varying temperatures are maintained by one compressor. In these cases, an evaporator pressure regulating (EPR) valve is installed at the outlet

Figure 16-14.-Solenoid valve and thermostatic control switch.

of each evaporator EXCEPT the evaporator in the space in which the lowest temperature is to be maintained. The EPR valve is set to keep the pressure in the coil from falling below the pressure corresponding to the lowest evaporator temperature desired in that space.

The EPR valve is used mostly on water coolers, on units where high humidity is required (such as fruit and vegetable stowage spaces), and in installations where two or more rooms are maintained at different temperatures by the use of the same refrigeration unit.

A cross section of a common EPR valve is shown in figure 16-15. The tension of the spring above the diaphragm is adjusted so that when the evaporator coil pressure drops below the desired minimum, the spring will shut the valve.

The EPR valve is not really a temperature control-that is, it does not regulate the temperature in the space. It is only a device that prevents the temperature from becoming too low.

Figure 16-15.-Exploded view of a typical evaporator pressure regulating (EPR) valve.