In practice, throttling devices, called either expansion valves or throttling valves, are used to reduce the refrigerant condensing pressure (high pressure) to the evaporating pressure (low pressure) by a throttling operation and regulate the liquid-refrigerant flow to the evaporator to match the equipment and load characteristics. These devices are designed to proportion the rate at which the refrigerant enters the cooling coil to the rate of evaporation of the liquid refrigerant in the coil; the amount depends, of course, on the amount of heat being removed from the refrigerated space. The most common throttling devices are as follows :
• thermostatic expansion valves,
• constant pressure expansion valves,
• float valves, and
• capillary tubes.
Note that a practical refrigeration system may consist of a large range of mechanical and electronic expansion valves and other flow control devices for small- and large-scale refrigeration systems, comprising thermostatic expansion valves, solenoid valves, thermostats and pressostats, modulating pressure regulators, filter driers, liquid indicators, non-return valves and water valves, and furthermore, decentralized electronic systems for full regulation and control.
