Expansion valve

Capillary, however, only small, simple devices such as refrigerators, because he is not capable of regulating the amount of fluid that is injected into the evaporator. Control valve must be used for this process are the most common thermostatic expansion valve, which consists of a casing valve capillary and bulb. Valve housing is fitted in the liquid line and the lamp is installed on the outlet of the evaporator.

This figure shows the evaporator and is powered by a thermostatic expansion valve. A small amount of fluid contained in the part of the lamp. The rest of the bulb, capillary tube and the space above the diaphragm in the valve body charged with saturated steam at a pressure corresponding to the temperature of the bulb. The space under the diaphragm in connection with evaporator pressure, therefore, equal to the pressure boiling.

The opening of the valve is:

• The pressure produced by the bulb temperature operating on the surface of the membrane.
• Pressure under the diaphragm, which is equal to the evaporating pressure.
• Spring pressure acting on the bottom of the diaphragm.

During normal operation, evaporation will stop at some distance up in the evaporator. Then, saturated gas appears which becomes overheated on its way through the last part of the evaporator. Bulb temperature, thus, the temperature of boiling-plus overheating, for example. at -10 C boiling point, temperature of the bulb may be 0 C.

If the evaporator has a low refrigerant vapor will continue to overheat, and the temperature at the outlet of the pipe will grow. Light bulb temperature will rise, and with it the steam pressure in the ball element because more charge to evaporate. Due to the increasing pressure of the diaphragm becomes forced down, the valve opens and more fluid enters the evaporator. Accordingly, the valve is closed if the light bulb temperature is lower.

Thermostatic valves are available in several versions and of course, there are many variations within each type of...