US3842616A

US3842616A - Refrigerant expansion device

Info

Publication number: US3842616A
Application number: US00430368A
Authority: US
Inventors: G Orbesen
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 1974-01-02
Filing date: 1974-01-02
Publication date: 1974-10-22
Anticipated expiration: 1991-10-22

Abstract

A thermostatic expansion device for controlling the flow of refrigerant to the evaporator of a compression refrigeration system and for preventing the flow of liquid refrigerant to the evaporator when the system is shut down. The foregoing flow prevention is achieved by the use of a spring-biased check valve which closes when the refrigerant pressure at the inlet of the expansion device is insufficient to overcome the spring pressure.

Description

United States Patent (191 Orbesen REFRIGERANT EXPANSION DEVICE [75] Inventor: G. Bradley Orbesen, Tully, NY. [73] Assignee: Carrier Corporation, Syracuse, NY. [22] Filed: Jan. 2, 1974 [2]] Appl. No.: 430,368

I1 I I 3,842,616

[ Oct. 22, 1974 Primary Examiner-Meyer Perlin Attorney, Agent, or Firm.l. Raymond Curtin; D. Peter Hochberg [5 7] ABSTRACT A thermostatic expansion device for controlling the flow of refrigerant to the evaporator of a compression refrigeration system and for preventing the flow of liquid refrigerant to the evaporator when the system is shut down. The foregoing flow prevention isachieved by the use of a spring-biased check valve which closes when the refrigerant pressure at the inlet of the expansion device is insufficient to overcome the spring pressure.

4 Claims, 4 Drawing Figures 5/1966 Leinbach 62/225 I REFRIGERANT EXPANSION DEVICE BACKGROUND OF THE INVENTION and they operate by flashing to gas, liquid refrigerant received by the device from the condenser. As the liquid refrigerant passes through the expansion device, the pressure and temperature of the refrigerant drop substantially and part of the refrigerant flashes to gas.

The most common metering device is the thermostatic expansion device which controls the flow of refrigerant by maintaining a relatively constant superheat at the discharge end of the evaporator coil to which the refrigerant flows from the device. Such devices generally comprise a valve which is movable to vary the size of a refrigerant expansion orifice in the valve. Movement of the valve is'controlled by a diaphragm. The diaphragm is subjected to the opposing forces of a spring and of pressure of refrigerant in the evaporator on one side, and of refrigerant pressure from refrigerant in a bulb associated with the evaporator on the other side. When the bulb pressure exceeds the combined pressures of the spring and the evaporator, the valve is moved to open the orifice to admit more refrigerant through the device into the evaporator, and when the bulb pressure falls below thatof the spring and evaporator, the valve is moved to close the orifice. The temperature of the refrigerant in the bulb is equal to the temperature of refrigerant at the end of the evaporator plus the amount of superheat of that refrigerant, and the pressure of the refrigerant in the bulb corresponds to this temperature. Therefore, the pressure of refrigerant in the bulb exceeds that of the refrigerant in the evaporator. The bulb pressure is transferred to the diaphragm by a capillary leading from the bulb to the device. The spring is selected to maintain a force on the diaphragm which will assure a control over the size'of the orifice which results in a desired value of superheat of refrigerant leaving the evaporator. Such maintenance of a value of superheat enables a high evaporator efficiency while preventing liquid refrigerant from reaching the compressor.

Although known thermostatic expansion devices have been highly successful in use, they have been found to have limitations when used with compressors whose motors have unusually low starting torques. One such motor is known as the permanent split capacitor type of compressor motor. The difficulty with prior thermostatic expansion devices is that upon shutdown, a relatively high pressure differential exists across the device which the compressor motor isunable to overcome when restarted. Therefore, prior thermostatic expansion devices have been modified to equalize the pressure across the device prior to the start-up of the compressor. This is accomplished by incorporating in the valve which alters the size of the expansion orifice,

a small bleed port which allows the high and low side pressures to equalize when the valve is in the closed position. Y

A shortcoming of the foregoing modified type of thermostatic expansion device is that the bleed port remains open at all times, and liquid refrigerant can flow or migrate through the device to the evaporator during an extended period in which the system is shut down. When the system is started up, the compressor is able to commence running, but liquid refrigerant may be carried to the compressor. This liquid refrigerant can mix with oil in the system and result in foaming which can cause excessive bearing wear and seizure of the compressor. Furthermore, liquid carry-over into the compressor can cause eventual valve, piston or rod breakage. The problems of liquid migration to the compressor increase with the amount of refrigerant in the system and are thus usually more severe with split system equipment in which the condenser and compressor are housed separately from the evaporator and in which the manufacturer frequently has no control over the refrigerantcharge which is put into the system.

SUMMARY OF THE INVENTION 7 An object of the present invention is to provide a refrigerant expansion device for use in a compression refrigeration system'which prevents the flow of liquid refrigerant through the device and toward the evaporator of the refrigeration system when the system is shut down. V I

A more particular object of the invention is to provide a thermostatic expansion device for a compression refrigeration system which dissipates any pressure differential across the device at the shutdown of the system that would prevent the compressor from restarting, and which prevents the flow of liquid refrigerant through the device while the system is shut down.

Another object of the present invention is to provide a thermostatic expansion device of the preceding type which is efficient in operation and economical to manufacture.- i v The preceding objects are achieved. according to' the preferred embodiment of the invention by the provision of a thermostatic expansion device having bleed ports for equalizing the pressure across the device upon shutdown of the compressor, and a check valve disposed in the refrigerant flow path through the device, the check valve being spring-biased to a closed position to prevent the flow of liquid refrigerant through the expansion device when the system is shut down. The foregoing spring pressure is overcome during start-up of the system by the pressure of refrigerant entering the device.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention in its preferred form comprises a thermostatic expansion device which includes an expansion orifice whose size is varied to control the flow of refrigerant through the device and to the evaporator of the compression refrigeration system in which the device is used, to maintain a predetermined amount of superheat of refrigerant leaving the evaporator. Means are provided for equalizing the refrigerant pressure across the device when the system is shut down from a running condition to reduce the starting torque required of the compressor motor when the system is restarted, and a check valve disposed in the device engages a valve seat to prevent the flow of refrigerant through the device when the system is shut down.

Referring now to the drawings, there is depicted in FIG. 1 a compression refrigeration system which includes a compressor 1, a condenser 3, a refrigerant expansion device in the form of a thermostatic expansion device 5 and an evaporator 7. These components are connected by refrigerant lines to form a refrigeration circuit. In operation, compressor 1 compresses refrigerant vapor and the vapor flows to condenser 3. The hot, compressed vapor gives off its heat in condenser 3 and condenses, and the liquid refrigerant flows through a high side refrigerant line 9 to expansion .device 5. Expanded refrigerant is discharged from device 5 through a low side line 11 which leads into evaporator 7. The refrigerant in the evaporator absorbs heat from an external heat exchange medium and vaporizes, and the refrigerant vapor proceeds back to compressor 1. Compressor 1 is presumed to be driven by a motor having a low starting torque such as the permanent split capacitor motor of the type referred to earlier.

Thermostatic expansion device 5 has several functions. During the normal operation of the system, the device is required to meter the flow of refrigerant to evaporator 7 to maintain a predetermined value of superheat of refrigerant leaving the evaporator. The construction of device 5 with regard to this function is known in the art. Thus, included in the body member 13 of device 5, is a diaphragm 15 which separatesa portion of device 5 into an upper chamber 17 and a lower chamber 19. A bulb 21 contains a quantity of refrigerant, and is affixed to the vapor discharge line of evaporator 7 in a known manner. The refrigerant pressure (or bulb pressure) normally exceeds the pressure in the evaporator because the refrigerant leaving the evaporator is superheated, and the bulb pressure corresponds to a refrigerant temperature equal to the superheat temperature. The lower side of diaphragm 15 is subjected to a spring pressure exerted by a spring 27 through a pair of parallel plungers 33 connected to a disc 28 on the underside of the diaphragm, and to the pressure of refrigerant leaving the evaporator. The refrigerant evaporator pressure can be transmitted to lower chamber 19 beneath diaphragm 15 by a refrigerant line 25 leading from the discharge line of evaporator 7 to device 5. Line 25 is attached to a coupling 29 in device 5 having a port 31 leading to the interior of the thermostatic expansion device. A second port 32 leads to lower chamber 19. A thermostatic expansion device incorporating a special line, such as line 25, for

transmitting the evaporator pressure to the device is' said to be externally equalized. Alternatively, the evaporator pressure can be transmitted to the device through the refrigerant discharge line of the device, and then transmitted to the chamber beneath the diaphragm by an internal port in the device. The latter thermostatic expansion devices are said to be internally equalized. Thus, the pressure across diaphragm 15 are the bulb pressure above the diaphragm, and the spring pressure and the evaporator pressure beneath the diaphragm.

The parallel plungers 33 are connected at their lower ends to a valve 35. Valve 35 cooperates with a first valve seat 37 to define an annular orifice therebetween when these elements are disengaged; refrigerant flowing through this orifice is expanded in a controlled manner prior to its discharge through an outlet 39. Plungers 33 are drawn upwardly when the evaporator pressure in lower chamber 19 exceeds the bulb pressure in upper chamber 17, thereby moving valve 35 toward a valve seat 37 to reduce the size of the expansion orifice. When the bulb pressure exceeds the evaporator pressure from line 25 and the pressure of spring 27, thus indicating that the superheat at theevaporator is excessive, diaphragm 15 moves downwardly carrying with it plungers 33. The latter movement opens valve 3S-to increase the flow of refrigerant through the annular expansion orificeRefrigerant flowing through the annular orifice is discharged through an outlet 39 leading to low side line 11.

The strength of spring 27 determines the amount of superheat maintained at the discharge line of evaporator 7. Spring 27 is confined between an adjusting plate 43 and the upper end wall 45 of the interior of valve 35. An adjusting screw 47 located in the threaded central orifice of a support member 49 effects the axial movement of plate 43 and hence the compression of spring 27. An end cap 51 protects screw 47 against inadvertent movement and prevents leakage from the device. Cap 51 can be removed from member 49 on which it is screwed to give access to the adjusting screw. When it is desired to increase the value of superheat of refrigerant leaving the evaporator, adjusting screw 47 is turned to raise adjusting plate 43, and to thereby compress spring 27. This has the effect of increasing the pressure on the lower side of diaphragm 15, which must be offset by an increased bulb pressure because the pressures on the diaphragm are equalized. Similarly, the superheat at the discharge of evaporator 7 can be reduced by turning adjusting screw 27 to lower plate 43, to reduce the compression of spring 27.

Device 5 is constructed to equalize the pressure across the valve during shutdown of the system to minimize the starting torque required of the compressor motor. Accordingly, as in prior art expansion valves used in systems requiring low initial back pressure during start-up of the compressor, bleed

ports

53 and 55 extend through valve 35. There is therefore communication across valve 35 even when the valve stem is engaged with valve seat 37. Unlike other thermostatic expansion valves wherein the closing of the valve to seal the expansion orifice would prevent the flow of refrigerant through the valve as during shutdown, prior valves having these bleed ports permit the deleterious flow of refrigerant through the expansion device when the system is shut down even though the valve is closed. The present invention provides means for preventing flow through the bleed ports when the system is shut down. Accordingly, a movable check valve 57 is located near the inlet 59 of device 5, and includes a piston portion 61 disposed in a piston chamber 63 and a checking portion 65 configured to engage a second valve seat 67 in a fluid sealing manner. As shown in FIG. 4, check valve 57 is disposed between plungers 33, and cylindrical interior surfaces of body member 13 are configured to hold the plungers and the check valve for sliding, reciprocating movement, while preventing refrigerant from flowing between these elements and the cooperating cylindrical surfaces. Check valve 57 is subjected to the pressure of a small spring 41, which engages piston portion 61 and urges check valve 57 to its downward position wherein checking portion 65 engages valve seat 67. Check valve 57 is also urged downwardly by the pressure of refrigerant entering port 31. A refrigerant port 69 located on the opposite side of piston portion 61 from port 31 gives refrigerant flowing through inlet 59 communication with the piston portion. The circumferential edges of piston portion 61 engage the internal walls of device 5 which define piston chamber 63 in a fluid sealing manner so that pressurized refrigerant cannot flow around the piston portion.

' When the refrigeration system is being shut down and compressor motor 1 is not running, check valve 57 is biased by spring 41 to its lowermost position as depicted in FIG. 2. While the refrigerant pressure beneath piston portion 61 is falling, the pressure across valve 35 is equalized through

bleed ports

53 and 55. When the refrigerant pressure at inlet 59 is no longer able to withstand the pressure of spring 41, the latter element moves check valve 57 downwardly until checking portion 65 is in fluid sealing engagement with valve seat 67. Any liquid refrigerant which may be in high side line 9 is precluded from flowing through device 5. When compressor 1 commences operation, refrigerant pressure builds up in inlet 59 and is exerted on the lower face of piston portion 61. When the latter pressure exceeds the opposing pressure of spring 41, check valve 57 is raised. By virtue of the pressure equalization which occurs across expansion device 5 when the systern is shut down, there is no initial pressure head for the compressor motor to overcome other than the small pressure of spring 41, and the compressor can start up satisfactorily.

Once the system has started up, device 5 functions in the conventional manner. Liquid refrigerant flows through inlet 59 and through the variable expansion orifice def ned by valve seat 37 and valve 35. The expanded refrigerant proceeds through outlet 39 and low side line 11 into evaporator 7. A portion of the expanded refrigerant which is at the discharge pressure from evaporator 7 is communicated to lower chamber 19 via refrigerant line 25. As long as the system is running, valve 35 is adjusted in response to the pressure differential across diaphragm to meter refrigerant into evaporator 7. When the system is shut down, check valve 57 is urged to its lower or closed position when the refrigerant pressure at inlet 59 falls below that of spring 27.

This embodiment of the invention achieves the objects set forth previously. There has been described a thermostatic expansion valve for a compression refrigeration system which dissipates any pressure differential across the valve during the shutdown of the system and which prevents refrigerant flow therethrough when the system is shut down. The valve is efficient and economical.

The invention has been described in detail with particular reference to a preferred embodiment thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

I claim:

1. A refrigerant expansion device for a compression refrigeration system, said device comprising:

a body member;

an inlet for admitting high pressure refrigerant into said body member;

an outlet for discharging expanded low pressure refrigerant from said body member;

means defining a refrigerant flow path between said inlet and said outlet;

expansion means comprising a first valve seat and a valve, said valve being movable relative to said valve seat for cooperating with said valve seat to define a variable size orifice in said refrigerant flow path for expanding refrigerant flowing through said orifice and said valve being engageable with said valve seat for sealing said orifice, and said valve including refrigerant passage means extending through said valve for equalizing the refrigerant pressure across said valve when said valve is engaged with said valve seat; and refrigerant flow preventing means including:

a second valve seat;

a check valve, said check valve being movable between a closed position wherein said check valve engages said second valve seat to close said flow path and an open position wherein said check valve disengages said valve seat;

means for moving said check valve to the open position when the refrigeration system is started up; and

means for moving said check valve to the closed position when the refrigeration system shuts down.

2. The invention according to claim 1 wherein said means for moving said check valve to the open position comprises a piston portion of said check valve, said piston portion being responsive to a predetermined high refrigerant pressure at said inlet to disengage said check valve from said valve seat. 3. The invention according to claim 2 wherein said means for moving said check valve to the closed position comprises biasing means for exerting pressure on said check valve to urge said check valve towards engagement with said second valve seat, whereby said check valve is moved from the closed position to the open position when the refrigerant pressure at said inlet exceeds the pressure exerted by said biasing means, and said check valve is moved to the closed position when the pressure exerted by said biasing means exceeds the refrigerant pressure at said inlet.

4. The invention according to claim 3 wherein said body member includes a piston chamber defined by interior walls of said body member and a refrigerant port leading from said inlet to said piston chamber, and said ,piston portion is disposed in said piston chamber and A dimensioned to engage said interior walls in a fluid sealing manner, said piston portion moving said check valve to the open position in response to a predetermined high refrigerant pressure at said inlet.

Claims

1. A refrigerant expansion device for a compression refrigeration system, said device comprising: a body member; an inlet for admitting high pressure refrigerant into said body member; an outlet for discharging expanded low pressure refrigerant from said body member; means defining a refrigerant flow path between said inlet and said outlet; expansion means comprising a first valve seat and a valve, said valve being movable relative to said valve seat for cooperating with said valve seat to define a variable size orifice in said refrigerant flow path for expanding refrigerant flowing through said orifice and said valve being engageable with said valve seat for sealing said orifice, and said valve including refrigerant passage means extending through said valve for equalizing the refrigerant pressure across said valve when said valve is engaged with said valve seat; and refrigerant flow preventing means including: a second valve seat; a check valve, said check valve being movable between a closed position wherein said check valve engages said second valve seat to close said flow path and an open position wherein said check valve disengages said valve seat; means for moving said check valve to the open position when the refrigeration system is started up; and means for moving said check valve to the closed position when the refrigeration system shuts down.

2. The invention according to claim 1 wherein said means for moving said check valve to the open position comprises a piston portion of said check valve, said piston portion being responsive to a predetermined high refrigerant pressure at said inlet to disengage said check valve from said valve seat.

3. The invention according to claim 2 wherein said means for moving said check valve to the closed position comprises biasing means for exerting pressure on said check valve to urge said check valve towards engagement with said second valve seat, whereby said check valve is moved from the closed position to the open position when the refrigerant pressure At said inlet exceeds the pressure exerted by said biasing means, and said check valve is moved to the closed position when the pressure exerted by said biasing means exceeds the refrigerant pressure at said inlet.

4. The invention according to claim 3 wherein said body member includes a piston chamber defined by interior walls of said body member and a refrigerant port leading from said inlet to said piston chamber, and said piston portion is disposed in said piston chamber and dimensioned to engage said interior walls in a fluid sealing manner, said piston portion moving said check valve to the open position in response to a predetermined high refrigerant pressure at said inlet.