Valves used in refrigeration machines can be simple capillary tubes of diameter 0.6 to 2.8 mm, or thermal expansion valves whose opening is controlled by the fluid temperature at the evaporator exit.

Two control modes are used: internal pressure equalization, which optimizes the filling of the evaporator, and external pressure equalization thanks to pressure sensor downstream of the evaporator, which compensates for its pressure drop

In terms of thermodynamics, an expansion valve is an adiabatic organ that produces no useful work. It performs what is called an isenthalpic throttling of the fluid passing through it. We also speak sometimes flash or flash expansion.

The icon of an expansion valve in Thermoptim is:

The enthalpy of the outlet point being equal to that of the inlet point, the expansion valve screen does not provide specific settings.

Knowing the pressure P2 and the enthalpy of the outlet point h1, the calculation of the state of this is done by searching temperature T2 such that h1 =  h(T2,P2).