A thermostatic expansion valve (TEV) is an important device in refrigeration and air conditioning systems.
It controls the amount of refrigerant entering the evaporator.
The TEV senses the temperature at the evaporator outlet and responds to the degree of superheat.
Superheat is the temperature difference between the actual refrigerant vapor temperature and its saturation temperature.
Maintaining proper superheat prevents liquid refrigerant from reaching the compressor, which could cause damage.
The TEV adjusts the flow automatically to keep the superheat at the desired level.
It does not directly sense load, general temperature, or pressure alone — only superheat.