Thermal Expansion Valve With Rapid Pressure Equalizer

Abstract

The thermostatic expansion valve is provided with an internal by-pass capable of providing rapid equalization of the pressure between the condenser and evaporator when the compressor shuts down. The valve controlling the refrigerant flow has an internal cavity in communication with the condenser pressure and a by-pass port in communication with the evaporator. The valve, urged towards the closed position by a spring, is actuated by the diaphragm through push pins. The push pins normally close the by-pass port, either by the lower end of one or more of the push pins cooperating with a seat located at the by-pass port outlet or a valve means (e.g. a flanged collar which guides the valve) interposed the push pins and the by-pass port. With the valve in the closed position, the push pin(s) or valve means can be lifted off the by-pass port by condenser pressure in the cavity, as forces across the diaphragm equalize after shutdown of the compressor. The system pressure is then rapidly equalized through the by-pass port.

Description

BACKGROUND OF THE INVENTION

This invention relates to refrigeration systems having means for rapid equalization of the pressure in the high and low pressure sides of the system.

In order to reduce the starting torque for a compressor in a refrigeration system, it is necessary to equalize the pressure between the suction and discharge side of the compressor after it has been stopped. Generally, when thermostatic expansion valves are used in refrigeration systems, this pressure equalization has been accomplished by one of two approaches. In one approach the thermostatic expansion valve is provided with a built-in bleed. The maximum size, and hence flow rate, of this bleed is limited by the minimum flow rate required during the operating cycle of the system. The bleed is usually limited to a rate substantially below that of the nominal capacity of the expansion valve. This limited bleed rate requires the system to be shut down for a considerable length of time to allow the pressures in the system to equalize. In some applications, time delay devices are employed to keep the system shut down until equalization is accomplished.

In another approach, the thermostatic expansion valve is provided with an internal by-pass such as that disclosed in U.S. Pat. No. 3,252,297. The valve disclosed by this patent includes an auxiliary valve which controls flow through a by-pass port. The auxiliary valve is maintained in the closed position by an auxiliary spring during normal operation. When the compressor is shut down, rising evaporator pressure opens the auxiliary valve and the system pressure is equalized through the by-pass port. Although thermostatic expansion valves of this type are capable of rapid equalization of the system pressure, the auxiliary spring and other additional parts required for the by-pass mechanism add to the complexity and cost of the valve.

SUMMARY OF THE INVENTION

The thermostatic expansion valve described in the abstract provides a by-pass system which is capable of providing rapid system pressure equalization, but is less complex and has fewer parts, and therefore, the overall cost of the valve is reduced.

When used in a refrigeration system, the expansion valve is connected in the system so that the underside of the diaphragm is subjected to evaporator inlet pressure and the top side is subjected to pressure of a thermal bulb feeling the temperature at the evaporator outlet. After the compressor shuts down, the evaporator warms up and the forces on the diaphragm tend to balance. The condenser pressure, acting against the diaphragm through the push pins, lifts the push pin(s) or valve means to open the by-pass ports and the evaporator and condenser pressures are equalized through the by-pass ports. Instead of requiring an auxiliary spring and other additional parts to provide the capability of rapid system pressure equalization, an internal cavity and a by-pass port are provided in the control valve with the by-pass port being maintained closed during normal valve operation through the cooperation of the superheat spring and push pins.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of an expansion valve, shown installed in a schematic representation of a refrigeration system, showing the internal by-pass in the closed position during normal operation.

FIG. 2 is a fragmentary view showing the internal by-pass in the open position during pressure equalization.

FIG. 3 is a fragmentary view showing an alternate arrangement for the internal by-pass.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Thermostatic expansion valve 10 is utilized in a refrigeration system including compressor C, condenser K, receiver R (optional) and an evaporator E. Expansion valve 10 has an inlet 12 connected to the outlet of the receiver and an outlet 14 connected to the inlet of the evaporator.

Needle valve 16 cooperates with valve seat 18 to control flow from inlet 12 to outlet 14. Valve 16 is urged towards the closed position by superheat spring 20 compressed between seat 22 (supported on the end of adjustment screw 24) and plate 26 mounted (and sealed) on the bottom of the valve. Flanged collar 28 fits slidably over valve 16 with flange 30 engaging the top of valve shoulder 32. Valve 16 has a central aperture 34 and an internal chamber 36 which permits condenser pressure to be applied to the underside of flange 30 through equalizing ports 38 located in shoulder 32.

Diaphragm 40 is clamped between cup 42 and head 44. Conduit 46 communicates between outlet 14 and chamber 48 so the underside of diaphragm 40 is subjected to the evaporator pressure. Thermal-sensing bulb 50, connected by capillary tube 52 to head 44, is in direct communication with chamber 54. Bulb 50 is charged with a temperature responsive charge and is strapped on the evaporator outlet. Thus, the top side of diaphragm 40 is subjected to a pressure which is the function of the evaporator outlet temperature.

Valve 16 is actuated towards the open position by push pins 56, the upper ends of which bear against diaphragm pad 58 and the lower ends of which bear against the top of flange 30 (In FIG. 1, the upper portion of the left push pin has been purposely omitted for clarity). Due to the spring 20 acting against diaphragm 40 through push pins 56, collar 28 and valve 16 remain engaged during normal valve operation until valve 16 seats.

When valve 16 is closed, push pins 56 and collar 28 are in the position shown in FIG. 1 and there is no flow between inlet 12 and outlet 14. The movement of spring 20 is limited by the seating of valve 16 so collar 28 is held in engagement with valve 16 only by diaphragm 40. As the evaporator warms up after compressor shutdown, the forces across diaphragm 40 tend to become balanced, so the condenser pressure in chamber 36 (acting against the diaphragm through push pins 56) can lift collar 28 from shoulder 32 as shown in FIG. 2. As collar 28 separates from shoulder 32, equalizing ports 38 are opened and the pressures of the condenser and the evaporator rapidly equalize. Collar 28 is returned to the seated position by diaphragm 40 (acting through push pins 56) after pressure equalization. Since equalizing ports 38 are normally closed they can be sized to obtain rapid pressure equalization.

In the alternate arrangement shown in FIG. 3, the lower end of push pin 60 cooperating with valve seat 62 in valve 64 acts as a by-pass valve to control flow through equalizing port 66. After compressor shutdown and the forces across the diaphragm are balanced, condenser pressure in chamber 36 (acting against the diaphragm through push pin 60) can lift the push pin from seat 62. As the push pin is lifted away from the seat, equalizing port 66 is opened and the pressures of the condenser and the evaporator rapidly equalize. With this arrangement, there is a well defined area upon which by-pass valve opening pressure in chamber 36 acts, and therefore, the pressure at which equalizer port 66 opens is more accurately controlled. Other valve means, such as a ball, interposed the push pin and seat 62 can be used to control the flow through equalizer port 66.

From the above description, it can be seen that the expansion valve of this invention includes an internal by-pass which is capable of providing very rapid system pressure equalization. The capability is provided without an auxiliary spring and other additional parts required by prior art valves. Hence, the design of the valve is simplified and the overall cost is reduced.

Claims

I claim:

1. In a thermostatic expansion valve having a body provided with an inlet and an outlet separated by a first seat, a control valve cooperating with the first seat to regulate flow from the inlet to the outlet, a diaphragm having one side subjected to a pressure which is a function of evaporator outlet temperature and its other side subjected to the pressure in said valve outlet means connecting the diaphragm to the valve to actuate the valve, a spring biasing the valve in the closing direction in opposition to the diaphragm, the improvement comprising:

a chamber in said control valve;

a conduit between the chamber and said inlet whereby inlet pressure prevails in said chamber;

a port leading from said chamber to said valve outlet;

a by-pass valve means controlling flow through said port, the pressure in said chamber acting on the by-pass valve means in a valve opening direction; and

said by-pass valve means being held closed by the diaphragm force until the spring closes the control valve on the first seat and the pressures across the diaphragm equalize sufficiently for the chamber pressure to open the by-pass valve means and equalize inlet and outlet pressures.

2. A thermostatic expansion valve according to claim 1 in which the control valve includes a second seat located at the outlet of said port and the means connecting the diaphragm and the control valve includes push pins, one of which cooperates with said second seat to act as said by-pass valve means.

3. A thermostatic expansion valve according to claim 2 in which the control valve is in the general form of a needle valve and the conduit is central of the needle valve.

4. A thermostatic expansion valve according to claim 1 in which the means connecting the diaphragm and the control valve includes push pins, said by-pass valve means being positioned between the push pins and the control valve whereby the spring acting on the control valve holds the by-pass valve means closed until the control valve closes on its seat.

5. A thermostatic expansion valve according to claim 4 in which the by-pass valve means comprises a plate overlying the port.

6. A thermostatic expansion valve according to claim 5 in which the control valve is in the general form of a needle valve and the conduit is central of the needle valve, said plate being annular.