US3054273A

US3054273A - Thermal expansion valve

Info

Publication number: US3054273A
Application number: US862260A
Authority: US
Inventors: William L Mcgrath
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 1959-12-28
Filing date: 1959-12-28
Publication date: 1962-09-18
Anticipated expiration: 1979-09-18

Description

Sept. 18, 1962 w. MOGRATH 3,054,273

THERMAL EXPANSION VALVE Filed D60. 28, 1959 LU K 3 m (I) ll] 0: O.

TEMPERATURE FIG. 3

INVENTOR.

WILLIAM L. MC GRATH ATTORNEY.

Unite tats 3,054,273 Patented Sept. 18, 1962 3,054,273 THERMAL EXPANSION VALVE William L. McGrath, Syracuse, N.Y., assignor to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware Filed Dec. 28, 1959, er. No. 362,260 14 (Ilaims. (Cl. 62-415) This invention relates to a refrigerating system and more particularly to improvements in valve mechanism adapted to control the flow of refrigerant from the condenser to the evaporator in a refrigerating system. Further this invention relates to a thermostatic refrigerant expansion valve mechanism and to a method for operating said valve mechanism.

Hand valves were originally provided in refrigerating systems to control the flow of refrigerant from the condenser to the evaporator. However their use was limited to systems operating under fairly con-stant loads for long periods of time. An attendant was required to adjust the valve in response to any change in suction pressure as shown on the suction gage.

Automatic expansion valves were introduced to provide better performance and to obviate the need for an attendant to regulate the valve. The automatic expansion valve was advantageous where it was desired to maintain a constant evaporator temperature but this valve does not re spond satisfactorily to varying loads. When the temperature surrounding the evaporator coil rises due to a greater heat load, the liquid refrigerant in the coil is all evaporated before any of it reaches the end of the coil, thus reducing the effectiveness of the evaporator coil. If there is insufiicient heat in the room to evaporate all the refrigerant entering the coil, there is nothing to prevent the unevaporated liquid from flooding back the suction line to the compressor and damaging the compressor.

Thermostatic expansion valves have superseded automatic expansion valves in many applications, for these valves respond readily to variation in load and balance the evaporator coil without allowing any flood back. Basically, the thermostatic expansion valve is similar to an automatic expansion valve but with a temperature sensitive element containing a volatile fluid charge mounted in contact with the suction line. The pressure thus created exerts a force tending to open the valve, counteracting the closing force from the pressure in the evaporator. Thus if the heat load drops so that unevaporated refrigerant approaches the outlet of the evaporator, the valve closes a little to reduce the flow of refrigerant therethrough. Under heavy loads the suction pressure will rise and may overload the compressor.

To guard against overloading the compressor, it has been proposed that protection be built into the expansion valve by adding a precise limited fluid charge so that it fades out and limits the suction pressure above a predetermined temperature. As the volume of the closed system is constant, heating and cooling of the fluid charge results in corresponding changes of the saturated vapor pressure. At the fade out temperature, the last of the liquid is vaporized. An additional rise in temperature then increases the pressure of the fluid only slightly because the fluid is now completely a vapor and the pressure change is only proportional to the change in absolute temperature. Since the pressure of the fluid does not increase significantly with further increase in temperature, the valve opens no wider and thereby limits the pressure in the evaporator to a predetermined operating pressure. In practice, however, the limited charge thermal sensitive system is not entirely satisfactory for it is virtually impossible to cut off accurately at a given fade out temperature and still maintain proper control at the normal balance temperature. The fade out temperature is generally several degrees higher than that desire A primary object of this invention is to provide a refrigerating apparatus of the compressor-condenser-expansion means-evaporator type in which the expansion means is controlled to prevent overloading the compressor.

Another object of this invention is to provide an improved more precise expansion valve mechanism.

Still another object of this invention is to provide a thermostatic expansion valve mechanism having an improved limited charged thermal sensitive element.

This invention relates to a refrigerating system having a compressor, a condenser, expansion valve means, and an evaporator. The expansion valve means comprises a body with a partition having a port therein dividing the body into a first compartment and a second compartment. The first compartment is connected with the condenser and the second compartment is connected with the evaporator. A valve coacts with said port to control refrigerant flow between the first and second compartments. A casing is mounted above said body and forms a part thereof. The casing is divided into a first chamber and a second chamher by a diaphragm, and a valve stem operatively connects said diaphragm with said valve. Thermal sensitive means responsive to the temperature in the suction line are in communication with the second chamber. The second chamber and the thermal sensitive means define a closed system. Control means responsive to a predetermined pressure and corresponding temperature in the suction line are provided for suddenly substantially increasing the volume of the closed system to prevent the suction temperature and hence pressure from rising above said predetermined pressure and overloading the compressor.

This invention also relates to a valve mechanism for controlling the flow of refrigerant to the evaporator of a refrigerating system. The valve mechanism comprises a valve body, a partition dividing the valve body into separate inlet and outlet compartments, a port in the partition, a valve in the outlet coacting with said port to regulate flow between the compartments, means urging said valve towards a closed position, a valve stem connected to the valve, a diaphragm connected to said valve stem, means for subjecting one side of said diaphragm to a vapor pressure responsive to a temperature at the evaporator outlet, means for subjecting the other side of the diaphragm to suction pressure, and yieldable means cooperating with said vapor pressure responsive means to greatly increase the volume thereof in response to a predetermined suction pressure.

Further this invention relates to a method of operating a thermostatic expansion valve mechanism having a limited liquid charged system comprising the steps of regulating the flow of refrigerant through the valve mechanism in response to the evaporator pressure and to the pressure in the limited liquid charged system, suddenly increasing the volume of the limited liquid charged system to vaporize the remaining liquid and limit the pressure in said system to a predetermined value, and thereafter above said predetermined value regulating the flow of refrigerant in response to evaporator pressure alone.

The foregoing and other objects of the invention will more clearly appear from the following detailed description of a preferred embodiment of the invention, particularly when considered in connection with the accompanying drawing, in which:

FIGURE 1 is a diagrammatic view of a refrigerating system embodying the improved thermostatic expansion valve mechanism;

FIGURE 2 is a sectional view of a modification of the thedrmostatic expansion valve mechanism of FIGURE 1, an

FIGURE 3 is a graph of pressure versus temperature showing the characteristics of the limited charge, thermostatic expansion-valve thermal sensitive element.

Referring first to FIGURE 1, there is shown a diagrammatic view of a refrigerating system including a motor compressor unit, generally referred to at 10, that delivers refrigerant to condenser 12 through discharge line 11. The condenser is air cooled by fan means 13. The refrigerant flows from the condenser 12 to receiver 14 from which it is delivered to thermostatic expansion valve mechanism 15. In some systems, the receiver is omitted and refrigerant flows directly from the condenser to the thermal expansion valve mechanism. The thermostatic expansion valve mechanism regulates the flow of refrigerant to evaporator 16. Fan means 17 passes air over the evaporator. Evaporator 16 is connected through suction line 18 to the inlet side of motor compressor unit 10.

The thermostatic valve mechanism includes a housing comprising body 19 and casing 28. Partition 29 divides body 19 into a first compartment or inlet chamber 22, and a second compartment or outlet chamber 23. The inlet 24 to chamber 22 is in communication with receiver 14 and condenser 12 and the outlet 25 is in communication with the evaporator. Located within chamber 23 is a valve 26 which coacts with valve port 21 in the partition 20 to regulate the flow of refrigerant from chamber 22 to chamber 23. The valve 26 is urged towards the closed position by means of spring 27 The pressure with which the spring urges the valve 26 to closed position may be varied by the usual adjusting means 27, preferably in the form of a screw.

Mounted above body 19 is a casing 28. Though shown separately, the body 19 and casing 28 can be formed as an integral housing. Diaphragm 29 divides the casing into an upper compartment 30 and a lower compartment 31. Secured to the diaphragm and to the valve 26 is a valve stem 32, movable reciprocably within the housing. Guide and seal 33 prevents communication between

compartments

22 and 31.

The upper compartment 30 is connected through a fitting 34 to a thermal sensitive means comprising capillary tube 35 and bulb 36 attached in heat exchange relation to suction line 18 adjacent the outlet of evaporator 16. A limited charge is introduced into bulb 36 and consists preferably of the same refrigerant employed in the system. The bulb contains both liquid and gas. Below a predetermined temperature at the bulb, the charge is partly in liquid phase and partly in vapor phase and above this temperature all of the charge is in vapor phase. The movable partition 29 preferably in the form of a flexible diaphragm (FIGURE 1) or a bellows (not shown) moves in response to fluid pressure changes resulting from the heating or cooling of the charge in bulb 36 in response to the difference in pressure between the two sides and therefore it moves to reflect changes in superheat in suction line 18. The movement of the diaphragm 29 is imparted to valve stem 32 connected thereto and to valve 26. The valve opening movement is opposed by the action of spring 27.

Because the thermostatic valve mechanism 15 depends primarily on the pressure differential between the evaporator pressure and the pressure of the bulb charge as infiuenced by the dfiired superheat in the suction line, any drop in pressure between the two points may disturb the necessary balance and adversely affect control. To overcome this drop in pressure, an external equalizer line 42 connecting suction line 18 with chamber '31 is generally employed. This small-diameter equalizer line 42 tends to create an average evaporator pressure opposing the movement of diaphragm 29.

Within cylindrical housing 37, forming a part of casing 28, is a control means comprised of expansible bellows 38 in communication with compartment 30 and spring 39 mounted between the bellows and housing 37. Spring 39 is designed to yield suddenly under a predetermined pressure. Adjusting means are provided to regulate the spring tension and are comprised of a spring cover 41 and an adjusting screw 40 operatively connected to housing 37. Port 43 is provided in the housing to permit proper expansion and contraction of bellows 38.

The compartment 30, tube 35, bulb 36 and bellows 38 comprise a closed limited fluid charged system. The pressure within the closed system is responsive to the temperature of refrigerant in the suction line or at a point near the evaporator exit. The density of the refrigerant determines the loading on the compressor but the pressure, temperature and density in the suction line are interrelated and any one of these conditions may be used to measure the degree of loading.

The thermostatic expansion valve mechanism 15 described above will maintain a substantially constant suction pressure at a predetermined maximum value. The adjustment of valve 26 is accomplished by means of screw 27 which regulates the spring 27 located in the compartment 23, so that any tension exerted will supplement the pressure in the evaporator. The tension of spring 27 must be equal to the pressure difference corresponding to the desired superheat temperature in the suction line. At that setting the valve would be in equilibrium when the suction temperature is at the desired superheat level. Any increase in superheat would upset the equilibrium by the subsequent rise in pressure in the closed system and would tend to move the valve away from port 21 opening the same. The valve movement would be proportional to the amount of superheat in excess of the desired level.

In use it has been found that where the valve is in equilibrium at, for example, 43 F. and the desired cutoff temperature is 46 F., it is virtually impossible to cutoff below 55 F. and still maintain proper control at the equilibrium. The desired characteristic of the thermostatic expansion valve mechauism-thermal sensitive means is shown on a pressure versus temperature graph in FIGURE 3 in the solid line, and the dotted line represents the characteristic of the simple limited fluid charged system thermostatic expansion valve mechanism-thermal sensitive means. The simple limited fiuid charged system is unable to cutoff accurately at a given pressure. In the conventional system, an increase in evaporator pressure calls for a reduced valve opening to maintain the same rate of flow and this adds to the unbalance pressure of port. The reduced valve opening produces a decrease in pressure of spring 27. The reduced valve opening also displaces the diaphragm 2 upwardly producing a decrease in volume and an increase in vapor pressure of the limited charged system. The effectiveness of spring 27 to maintain the equilibrium is diminished and the effect of both reduced valve opening and increased port unbalance, is the establishment of a new balance point at a higher suction pressure. By virtue of my improved thermostatic valve mechanism, the bellows 38 shown in FIGURE 1 will suddenly expand at approximately 46 F. With the sudden large increase in volume in the limited charged system, the remaining liquid will be vaporized quickly at the fade out point indicated at 48 in FIGURE 3. All the fluid in the limited charged system is then in the form of saturated vapor. The constant pressure-temperature relationship no longer holds and as the suction temperature increases above the fade out point, superheating occurs accompanied by only a very slight pressure rise. It is thus seen that the sudden increase in volume provided by the yieldable means or bellows 38 provides a more precise control to limit refrigerative load on the compressor and thus prevent overloading of the compressor.

In FIGURE 2 there is shown a modification of my thermostatic expansion valve mechanism. The construction of the valve housing is the same as that of the embodiment shown in FIGURE 1. Connected to compartment 30 is a thermal sensitive means comprised of capillary '5 tube 45 and feeler bulb 46. Within the feeler bulb is a yieldable or collapsible member 47 in the form of a hermetically sealed bellows or synthetic rubber sack. Member 47 is charged with air or gas to a predetermined pressure. The capillary tube 45 is connected to casing 48 through the fitting 44.

The yieldable or collapsible member 47 functions in the same manner as the bellows '38 to prevent overloading of the compressor. When the temperature in feeler bulb 46 rises to the desired predetermined pressure, the pressure outside of member 47 will be greater than that inside and the member 47 will collapse thereby suddenly increasing the volume of the limited charged system and causing the valve to operate as a constant pressure valve in the same manner as described above.

The improved thermostatic expansion valve mechanism incorporating a relatively simple and inexpensive yieldable control means prevents overloading of the compressor motor. Further the thermostatic expansion valve mechanism employing yieldable means to quickly materially increase the volume of the limited charged system at a predetermined temperature is much more precise and accurate than thermostatic valves heretofore known and the performance of the refrigerating system incorporating my thermostatic valve mechinism is materially improved.

While I have described and illustrated a preferred embodiment of my invention, it will be understood that my invention is not limited thereto since it may be otherwise embodied within the scope of the following claims.

I claim:

1. In a refrigerating system, the combination of a compressor, a condenser, expansion valve means and an evaporator connected in such order by means including a discharge line and a suction line, said expansion valve means comprising a body, a partition having a port therein dividing said body into a first compartment and a second compartment, said first compartment communicating with said condenser and said second compartment communicating with said evaporator, a valve coacting with said port to control refrigerant flow between the condenser and the evaporator, a casing mounted on said body, a diaphragm dividing said casing into a first chamber and a second chamber, an equalizer line connecting said first chamber to said suction line, means operatively connecting said diaphragm and said valve, thermal sensitive means responsive to the temperature, in the suction line adjacent the evaporator in communication with said second chamber, said second chamber and said thermal sensitive means defining a closed system, said closed system containing a limited charge, and control means responsive to a predetermined condition in the suction line for suddenly substantially increasing the volume of said closed system to prevent the suction pressure from rising above said predetermined condition and overloading the compressor.

2. In a refrigerating system, the combination of a compressor, a condenser, expansion valve means and an evaporator connected in such order by means including a discharge line and a suction line, said expansion valve means comprising a body, a partition having a port therein dividing said body into a first compartment and a second compartment, said first compartment communicating with said condenser and said second compartment communicating with said evaporator, a valve coacting with said port to control refrigerant flow between the first and second compartments, a casing mounted on said body, a movable partition dividing said easing into a first chamber and a second chamber, means operatively connecting said movable partition and said valve, means for imposing evapo rator pressure in the first chamber, thermal sensitive means responsive to the temperature in the suction line in communication with said second chamber, said second chamber and said thermal sensitive means defining a closed system, said closed system containing a limited charge, and control means responsive to a predetermined condition in the suction line for rapidly increasing the volume of said closed system to prevent the suction pressure from rising above said predetermined condition and overloading the compressor.

3. A refrigeration system comprising in combination a compressor, a condenser, expansion valve means, and an evaporator connected in such order by means including a discharge line and a suction line, said expansion valve means comprising a housing having a body portion and a casing portion, a fixed partition dividing said body portion into a first and a second compartment, said partition having a port therethrough, said first compartment being in communication with said condenser and said second compartment being in communication with said evaporator, a valve coacting with said port to throttle flow between the first and second compartments, a flexible movable partition in said casing portion dividing same into a first and a second chamber, means for imposing evaporator pressure in the first chamber, a bellows in said second chamber, a spring adapted to compress said bellows and deflect substantially in response to a predetermined pressure in the bellows, said second chamber being operatively connected to a bulb containing a limited fluid charge mounted adjacent said suction line, said second compartment, bellows, and bulb defining a closed system whereby when the temperature in the suction line exceeds a predetermined value, the charge in said bulb expands causing the bellows to rapidly expand greatly increasing the volume of the closed system and evaporating the last of the fluid therein, after which the valve means will function to prevent the suction pressure from rising above the predetermined value.

4. In a refrigerating system, the combination of a compressor, a condenser, expansion valve mechanism and an evaporator connected in such order by means including a discharge line and a suction line, said expansion valve mechanism comprising a housing, a passageway for refrigerant through said housing, valve means in said housing for regulating flow of refrigerant through said passageway, means responsive to the temperature of refrigerant in said suction line for moving said valve means toregulate the flow of refrigerant through the housing, said temperature responsive means including a movable partition in said housing, means for subjecting one side of said movable partition to a vapor pressure responsive to a temperature at the evaporator outlet, means for subjecting the other side of said movable partition to suction pressure, said temperature responsive means comprising a closed system containing a limited charge, and control means cooperating with said temperature responsive means to prevent the suction pressure from rising above a predetermined pressure and overloading the compressor, said control means including a yieldable member in communication with said means for subjecting one side of said movable partition to a vapor pressure responsive to a temperature at the evaporator outlet to greatly increase the volume thereto in response to a predetermined suction temperature.

5. A valve mechanism for controlling the flow of refrigerant to an evaporator of a refrigerating system comprising a valve body, a partition dividing said valve body into an inlet compartment and an outlet compartment, a valve seat port in said partition, a valve located in said outlet compartment and cooperating with said valve seat port to regulate refrigerant flow between said inlet and outlet compartments, a spring urging said valve towards a closed position, a casing on said valve body, a diaphragm dividing said casing into a first chamber and a second chamber, said diaphragm being connected to said valve, said first chamber adapted to be maintained at suction pressure, said second chamber connected to a limited fluid charged system, having a bellows connected thereto adapted to be suddenly expanded in response to a predetermined temperature sensed by the limited fluid charged system, whereby, above said predetermined temperature said valve mechanism acts to limit the suction pressure from rising substantially above a predetermined value.

6. A valve mechanism for controlling the flow of refrigerant to an evaporator of a refrigerating system comprising a valve body, a partition dividing the valve body into separate inlet and outlet compartments, a port in said partition, a valve in said outlet compartment coacting with said port to regulate flow between said compartments, a valve stem connected to said valve, a movable partition connected to said valve stem within said valve body, means for subjecting one side of said movable partition to a vapor pressure responsive to a temperature at the evaporator outlet, said means containing a limited charge means for subjecting the other side of said movable partition to suction pressure, and yieldable means cooperating with said first means to greatly increase the volume thereof in response to a predetermined suction temperature.

7. A valve mechanism as in claim 6 including means urging said valve toward a closed position.

8. A valve mechanism as in claim 6 wherein said yieldable means includes an expansible bellows.

9. A valve mechanism as in claim 8 wherein said yieldable means includes a spring adapted to yield suddenly at said predetermined suction temperature to permit rapid expansion of said bellows to preclude increase in suction pressure substantially above a predetermined value.

10. A valve mechanism for controlling the flow of refrigerant to an evaporator of a refrigerating system comprising a valve body having an inlet and an outlet and an interconnecting passageway therebetween, a partition in the passageway cooperating with the valve body to form a first compartment and a second compartment, said partition having an opening therein, a valve coacting with said opening to regulate flow of refrigerant through said passageway, a valve stem operatively connected to said valve, a diaphragm connected to said valve stem within said valve body, means for subjecting one side of said diaphragm to a fluid pressure responsive to temperature at the evaporator outlet, means for subjecting the other side of said diaphragm to suction pressure, and means responsive to a predetermined temperature at the evaporator outlet to greatly increase the volume of said first means and render said first means insensitive to increase in temperature above a predetermined value whereby the suction pressure is prevented from rising substantially above a predetermined value.

11. A valve mechanism as in claim 10 wherein said means responsive to a predetermined temperature comprises an expansible bellows operatively communicating with said means for subjecting one side of said diaphragm to a fluid pressure to greatly increase the volume thereof.

12. A valve mechanism as in claim 10 wherein said means responsive to a predetermined temperature comprises a hermetically sealed collapsible member.

13. A method of operating a thermostatic expansion valve mechanism in a refrigerating system comprising a compressor, a condenser, a thermostatic expansion valve having a limited charged thermal sensitive system and an evaporator connected in refrigerant flow relationship comprising the steps of compressing vaporous refrigerant, condensing the compressed refrigerant, regulating the flow of refrigerant through the thermostatic expansion valve mechanism in response to the superheat near the evaporator exit, preventing the pressure in a thermal sensitive system from rising substantially above a predetermined value by collapsing a movable member in response to a condition of the refrigerant at the evaporator exit to convert all the charge to vapor, regulating the flow of refrigerant through said valve mechanism in response to evaporator pressure above said predetermined value, and placing refrigerant in the evaporator in heat exchange relation with air passing thereover thereby cooling the air.

14. A method of operating an expansion valve in a refrigerating system comprising the steps of exerting a valve-opening force in response to the pressure in a thermal sensitive system containing a limited liquid charge, exerting a valve-closing force in response to evaporator pressure, yieldably opposing the valve opening force, exerting a valve-opening force in response to an increase in temperature in the suction line, and converting all the liquid in the thermal sensitive system to vapor at a predetermined temperature by rapidly increasing the volume of the thermal sensitive system to prevent the pressure in said thermal sensitive system from rising substantially above a predetermined maximum value.

References Cited in the file of this patent UNITED STATES PATENTS 1,971,695 Ploeger Aug. 28, 1934 2,220,998 Holmes Nov. 12, 1940 2,264,545 Newton Dec. 2, 1941 2,399,088 Andrews Apr. 23, 1946 2,571,625 Seldon Oct. 16, 1951 2,755,025 Boles July 17, 1956 2,786,336 Lange Mar. 26, 1957 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent-N0, 3,054,273 A September 18, 1962 William Lo McGrath that error appears in the above numbered pat- Patent should read as It is hereby certified ent requiring correction and that the said Letters corrected belo* Column 2, line 41, column 4, line 47, for "'2" read 29 Signed and sealed this 3rd day of September 1963,

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer DAVID L. LADD Commissioner of Patents