How does thermal expansion valve works?
The thermostatic expansion valve needs capillary tube and thermal element (bulb) to work. The capillary tube connects the element to the top of TXV diaphragm. Here is what it looks like: The element (sensing bulb or thermal bulb) is partly filled with a liquid refrigerant (usually the same refrigerant used in the system) and maintains some liquid under all conditions of temperature and load. A cross section of a thermostatic expansion valve components and the operation principle are showing below. The three forces which control the operation of the thermal expansion valve are: P1 The vapor pressure of the thermostatic element (a reaction to the bulb temperature) which acts to open the valve. P2 The evaporator pressure which acts in a closing direction below the diaphragm. P3 The pressure equivalent of the superheat spring force which is also applied underneath the diaphragm in a closing force. At any constant operating condition, these forces are balance. Therefore, P1=P2+P3 When a cha
