Automatic Expansion Valve Design
As the evaporator pressure decreases, the pressure difference effect of the bellows, to the valve body. Being attached to the needle, it will open the needle valve. Some liquid refrigerant will spray evaporator. Because the refrigerant evaporates at a constant low-pressure evaporator and the Cabinet temperature remains within design limits.
Expansion valve only opens when the pressure drops in the evaporator. Pressure drop occurs only when the compressor is running. The expansion valve, however, will not flood the low side when the compressor is running. When boiling of refrigerant, liquid, spray and steam until the end of the evaporator motor control will be cool. This engine management (sensing bulb) is connected to the suction line. The switch will open and stop the motor. Low pressure will build up enough to close the expansion valve.
These valves are adjustable. They permit the opening of the needle valve in a wide pressure range. Expansion valves shall be set to the atmospheric pressure, P1, which affects their activities.
High altitudes will cause a decrease in atmospheric pressure. Adjusting screw should be turned in to compensate for the lower atmospheric pressure. Refrigerants with different pressure boil have different expansion valve settings.
There are many different designs of automatic expansion valve. Flexible part is either aperture, Fig. 5-2, or furs. As a rule, is made of phosphor bronze and brazed or soldered to the valve body. Flexible elements need to go beyond time after time, without sacrificing flexibility. Valve body, as a rule, forged brass, but sometimes he threw. It must be the drainage water (leaks) proof. The liquid at the inlet has or soldered connections, flanges, flared connections, or pipe thread. He usually has a screen for easy removal. Hie screen is made of brass or stainless steel wire 60 to 100 mesh. (This means that 60 to 100 holes per square inch.)
Tt is important to remember that the valve capacity should equal the performance of the evaporator. The liquid refrigerant flowing past the expansion valve needle same weight as the pair (gas) pumped from the compressor.
Use one ton valve with one ton of condensing unit. Under valve capacity, as a rule, starve evaporator (too little refrigerant passes). In overcapacity valve, as a rule, allow too much of the refrigerant in the evaporator, when the valve is opened. This can cause sweat to back or frost back on the suction line.
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