Simple thermostatic expansion valve is based on the pressure under the diaphragm is nearly the same as at coil outlet, and small coil pressure differences can be accommodated by adjusting spring setting.
Where the evaporator is divided into a number of parallel passes, switchgear with small pressure loss is used to provide an equal flow through every aisle. Pressure drop in 1-2 bar are common. There will now be a much more finite difference between the pressure under the diaphragm and that the coil inlet. To correct this, in valve body varies in accordance with the middle of the chamber and the levelling compound, which is given at coil outlet, not far from the bottle position. Most thermostatic valves have provision for external equalizer connection (see Fig. 8.4).
Thermostatic expansion valve in a much continuous proportional operation and constantly hunted, although the amplitude of the swing can be limited by proper selection and installation, and if the valve has a range of design range of mass flow.
Difficulties arise when the compressors operate at reduced loads and refrigerant mass flow falls below the design of the valve range. This is useful to keep condensing pressure to a steady, albeit not have a permanent and, as a rule, you can get in cold weather to save the power of the compressor.
Valves for small systems can be considered completely closed and completely open at times. Overfishing thermostatic expansion valve means that the surface of the evaporator misfeeds refrigerant, which led to a slight loss of heat transfer efficiency. If hunting is caused by a time lag between a change in the valve position and the effect on the output, the solution may be to increase the weight sensor phial, which would increase the attenuation. Oversized valves and wrong phial position can lead to hunting. The bottles must always on the horizontal output as close as possible to the evaporator as possible, not on the lower part of the pipe. Electronic expansion valves are now becoming increasingly popular for many applications.....
