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Thermostatic expansion valve - Feeler bulb thermostatic expansion valve

Technical information Refrigeration Thermostatic expansion valve

Thermostatic expansion valve

Automatic expansion valve thermostatic expansion valve, often abbreviated TXV, has a membrane with a needle and a seat under it. It differs in that the adjustment spring below the diaphragm, and not over it. Pressure on the underside of the diaphragm is a combination of the evaporator pressure spring. The pressure on the top of the diaphragm comes from a small cylinder, called remote sensing bulb, or trial balloon lamp." This lamp is charged with the refrigerant, or other suitable chemical substance that increases the pressure on the top of the bellows, as the temperature of the refrigerant pipe to which it is securely connected, increases. A fine-mesh strainer, as a rule, is included at the valve inlet to prevent valve become plugged debris that may be distributed with the refrigerant.

To see how TXV works, suppose the adjustment spring is set to maintain 10F overheating in remote sensing bulb location (evaporator).

This is normal, most valves are supplied from the factory set for the period from 7F and 10F overheating. As long as overheating, measured in the sensing bulb consistent with those of the adjustment spring is set, the diaphragm is in the horizontal position. She moves up, down. The cooling capacity of the refrigerant flow through the valve, and through the evaporator are in equilibrium with the cooling load. The needle remains at the specified position. The combined pressures of the evaporator and spring below the diaphragm, equal to the pressure of the sensing bulb over her.

If the superheat drops below 10F, however, the temperature of the refrigerant from the evaporator drops. It is felt through the suction line of remote sensing bulb. Saturated refrigerant pressure and temperature inside the lamp drop; this sends a reduced pressure on the upper side of the diaphragm. The United efforts of the spring and pressure boiling point below the diaphragm is currently in excess of the sensing bulb over her and aperture is bent up. The needle moves toward the closed position, allowing a smaller refrigerant to enter into the evaporator. Reduction of refrigerant flow increases overheating, returning the system to equilibrium at 10F overheating.

If overheating rise above 10F, saturation temperature of the refrigerant pressure and in the framework of remote sensing grow lamps. This sends increase the pressure on the upper side of the diaphragm. Combined pressure in the evaporator and spring below the diaphragm is now less than the pressure on him. Aperture leans down move the needle in the direction of the open position; this action enables more refrigerant to enter into the evaporator. As more refrigerant enters the evaporator, the amount of overheating per pound decreases the refrigerant system, then returns to equilibrium at 10F overheating.

Now let's look at the actual pressure in the valve. We assume that the system is removed with R-22 and adjustment spring is set 15,0 square inch, which corresponds to 10F superheat for R-22 40F saturation temperature.

In equilibrium, the system cooling load consistent power. Refrigerant flow into the evaporator is just right for the production of 10F overheating of the refrigerant gas on remote sensing bulb place. For all practical purposes, the actual (hot) gas temperature in the suction line on remote sensing bulb location corresponds to the saturation temperature of the liquid/vapor-gas mixture inside the sensing bulb, pipes, connected to it and the top of the diaphragm in the thermostatic expansion valve. This will be true, however, only if the sensing bulb tightly clasped to clean, straight stretch near the suction line in the output. Sensitive lamp is intended for the sense of refrigerant gas temperature; it should not be located on the bottom of the suction line, or other places where it will measure temperature of liquid refrigerant, if he accidentally the suction line. When installed, it must be wrapped with waterproof (as a rule, closed-cell) insulation right along with the suction line. Insulation should extend at least one foot for a light bulb in each direction. Always refer to the instructions for setting up hardware for the correct location of the lamp.

Here we have assumed that the evaporator pressure-69.0 pounds per square inch. This corresponds to the saturation temperature 40F. Since gas is superheated 10F; actual temperature of the gas in the suction line of the equilibrium state is 50F...

 
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