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 BPHE 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 BPHE evaporator that would be needed to compensate for variations in superheating.