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Thermostatic valves
Thermostatic valves are used on most commercial systems. A typical example is shown in Fig. 26. Pressure in refrigerant circuit is removed through the holes, and refrigerant flow is regulated by a needle valve and diaphragm arrangement. The diaphragm moves pressure generated inside the control phial, which senses the temperature of the refrigerant from the evaporator. It should be about 5C above the boiling point, to make sure of no return liquid refrigerant in the compressor.
This temperature difference (overheating) is set by adjusting the pressure spring. Correct installation is vital for efficient and reliable operation of the system. If the load changes to the evaporator, the refrigerant temperature at the outlet of the evaporator is also changed. Control phial it feels, and automatically configures the refrigerant flow to account for changes in load.
The main disadvantage of thermostatic valves is that they do not work well, if the pressure difference between them is significantly reduced, for example. if the condensing pressure floats down with the fall of the ambient temperature. To cope with such conditions, balanced port and electronic expansion valves can be used.
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