Cross-Charged Thermal Expansion Valves

Please note that on 45F, temperature changes of approximately 5.5F produces pressure change 5 pounds per square inch, while in 20F, temperature changes of approximately 13 F is required to produce the same 5 psi pressure change. Therefore, the amount of overheating needed to obtain the desired increase in the sensing bulb increases the pressure and the temperature of the evaporator reduces. Based on this characteristic, tine number of overheating, necessary for the modulation of the needle TXV at low temperatures becomes excessive, in applications in which the sensing bulb charged with the same refrigerant in the system. Therefore, the effective area of heat transfer in the evaporator decreases as overheating requirements increase.

For low-temperature applications, TXVs enable cross-charged sensing bulb that uses refrigerant in the system. Bulbs refrigerant usually has a boiling point below, system refrigerant so that its pressure changes in the degree of suction superheat is more significant in the desired temperature of the evaporator. This strategy allows TXV work with a reasonable amount suction superheat, maintaining the effectiveness of the system.

Expansion valves, whose balls charged with liquids, than other systems of the refrigerant, are called cross-charged TXVs. This term is used because the answers are shown on the chart, pressure, temperature curve die balls refrigerant crosses pressure temperature curve of the systems of refrigeration-l ant. The curve is the temperature-pressure response system refrigerant. Curve temperature-pressure response of the refrigerant in the sensing bulb. Curve pressure-temperature response for TXV calibrated to 5 overheating. Pressure temperature curve of the lamp (B) a few! than flatter than that of the curve system refrigerant s (A). Consequently, increases the pressure in the evaporator, a greater number of overheating is necessary to bring the valve in the balance. Most overheating requirement evaporator at high temperatures gives a cross-charged TXVs pressure, limitations affect that provides a higher level motor overload protection and compressor flood back on start-up.

Liquid cross-charged expansion valves are not limited to low temperatures. They are also widely used in medium - and high-temperature commercial applications where pressure-limiting better. In such applications, diey is often preferable to gas-chargea pressure limit expansion valves, because they are less prone to hunting and installation of sensing bulb is not as critical. Such cross-charged valve operates satisfactorily widiin limited temperature range, as well as several different types of cross charges are available to die various temperature ranges. When ordering cross-charged valve, the temperature range must be stated so that the valve with proper cross-charge received...