Expansion Valves

Expansion Valves are devices used to control the refrigerant flow in a refrigeration system. They help to facilitate the change of higher pressure of liquid refrigerant in the condensing unit to lower pressure gas refrigerant in the evaporator.

In direct expansion circuits the two main types are thermostatic expansion valves and Electronic Expansion Valves. The thermostatic functionality of both internal equalisation and external equalisation is described with reference to diagrams. Electronic types are divided into categories of pulse width modulated and continuous modulation. Further types that use a fixed orifice are found in small systems and are either capillary tubes or restrictors. The flow of liquid into a flooded evaporator can be controlled by a float valve. This may be a high- or low-pressure type. Low-pressure types are use in low-pressure receiver circuits. Other level controllers are briefly covered.

The term “low side” is used to indicate the part of the system that operates under low pressure, in this case the evaporator. The “high side” is used to indicate the part of the system that operates under high pressure, in this case the condenser.