This valve is fitted in the suction line to control the pressure in the evaporator, to prevent it dropping below a predetermined pressure. It is used to control the evaporating temperatures of systems such as drinking water fountains and beverage coolers, to maintain a constant evaporator pressure/temperature and prevent freezing.
It is also used in multi-evaporator systems, when it is installed in the suction line of the warmest evaporator. Check valves or one-way valves are necessary to prevent migration of refrigerant from the warmer to the cooler evaporators during off cycles (see Figure 84).