Automatic valves operate with a constant counter-pressure that regulates the mass flow of refrigerant through the valve to obtain a constant evaporation pressure, as shown in Figure 4.12. The automatic valve, or constant pressure valve, can be used in systems with small variations in heat load and a maximum of one evaporator. The technology is old-fashioned, and is now often replaced by the more advanced thermal expansion valve.
An automatic valve could be used successfully with a brazed plate heat exchanger evaporator. However, the difference in cost compared with a thermal expansion valve would be less than the cost of the extra heat surface area in the brazed plate heat exchanger evaporator that would be needed to compensate for variations in superheating.