Abstract: The thermostatic expansion valve capsule is shown mounted in a cavity in a receiver of a widely used device. The exterior of the valve body utilizes two or three O-ring seals to achieve the proper connections in the installation. The temperature responsive charge in the head chamber above the diaphragm controls the movement of the valve in accordance with the temperature of the returning refrigerant, liquid or vapor, coming from the evaporator in an automotive air conditioning system. It is necessary to keep control in accordance with that temperature and, therefore, the temperature of the refrigerant leaving the expansion valve must not influence the head chamber temperature.

Abstract: The interior of the bellows is sealed at atmospheric pressure so the pressure on the outside of the bellows is resisted by the atmospheric pressure within the bellows as well as by the spring. When the pressure on the outside of the bellows (which is evaporator pressure in a refrigeration system) exceeds a predetermined amount, the bellows tends to collapse and the head of the bellows pulls away from the actuating pin and allows the spring acting on the pilot valve to open the pilot valve whereupon the pressure to the right of the head of the piston is reduced, allowing the piston to move to the right against the return spring force and thus open the outlet by moving the end of the piston wall past the slot in the stationary sleeve. When the pressure falls below the desired amount, the bellows expands and moves the head of the bellows against the actuating pin to close the pilot valve.