Adual-pressure regulator is shown in Fig. 10-24. It is used on a shell-andtube cooler. The dual-pressure regulator is particularly adaptable for the control of shell-and-tube brine or water coolers, which at intervals may be subjected to increased loads. Such an arrangement is shown in Fig. 10-24.
The high-pressure diaphragm is set at a suction pressure suitable for the normal load. The low-pressure diaphragm is set for a refrigerant temperature low enough to take care of any intermittent additional loads on the cooler. In this case, a thermostat affects the transfer between low and high pressure. The remote bulb of the thermostat is located in the wateror brine-line leaving the cooler. A temperature increase at this bulb indicating an increase in load will cause the thermostat to open the electric pilot and transfer control of the cooler to the low-temperature diaphragm. Upon removal of the excess load, the thermostat will cause the electric pilot to close the low-pressure port. The cooler is then automatically transferred to the normal pressure for which the high-pressure diaphragm is set. The diaphragms may be set at any two evaporator pressures at which it is desirable to operate. Any electric switching device responsive to load change may be used to change from one evaporator pressure to the other.