CA2063026C - Refrigerator system with subcooling flow control - Google Patents

Abstract

A vapor compression refrigeration system for cooling a cabinet having a thermostat for cycling the com-pressor off and on to maintain a predetermined temperature range in the cabinet includes a subcooling flow control valve at the inlet to the capillary tube restriction. The valve is operated by a sealed bellows containing a refrigerant so that the valve is responsive to the fluid entering the valve.
The valve is calibrated so that only a subcooled liquid refrigerant can flow through the valve and if the entering refrigerant is above a predetermined level the valve will close to completely block all flow between the condenser and the evaporator, and the valve will stay in the closed posi-tion at all times when the compressor is not running.

Description

REFRIGERATION SYSTEM WITH SUBCOOLING FLOW CONTROL

2 This invention relates to refrigeration systems, 3 and more particularly to refrigeration systems used in 4 household refrigerators and freezers.
Refrigeration systems for household refrigerators 6 and freezers have heretofore been designed for low cost and 7 high rellability, both of which require a simplicity of 8 design, together with a minimum number of parts. Typical 9 refrigerators or freezers employ a vapor-compression system having a fractional horsepower, electric motor driven, 11 hermetic compressor connected in a circuit with a condenser, 12 an evaporator, an optional accumulator, and a refrigerant 13 flow restriction between the condenser and the evaporator.
14 For reasons of obtaining high energy efficiency, it is desirable to utilize a relatively high duty cycle for the 16 compressor run time, while maintaining a sufficient reserve 17 for high ambient temperature conditions. Thus, a thermostat 18 responsive to the temperature in the cooled cabinet is used 19 to cycle the compressor as necessary to maintain the prese-lected temperature. Based on normal room temperatures and 21 the absorption of heat into the cooled space through the 22 insulation, the compressor duty cycle may run fifty percent 23 to sixty percent, leaving a reserve but requiring continuous 24 operation under very high ambient temperatures or fr~quent opening of the door for access to the interior of the cooled 26 cabinet.
27 The flow restriction has been almost universally 28 a capillary tube sized for optimal efficiency at a single set 29 of conditions of ambient and internal cabinet temperature.
Capillary tubes used as the sole restriction offer the 1 advantages of low cost, high reliability, and the added 2 efficiency of being easily placed in heat exchange relation-3 ship with the return line from the evaporator to the compres-4 sor.
The capillary tube system, which runs constantly 6 at a single ambient temperature and constant load condition, 7 is very efficient when the capillary tube is sized for these 8 conditions. When this is done and the system is operating 9 under equilibrium conditions, the refrigerant at the condens-er outlet where it enters the capillary tube is a saturated 11 or slightly subcooled liquid. This liquefied refrigerant 12 flows through the capillary tube and undergoes a substantial 13 pressure reduction until it enters the evaporator, where it 14 is vaporized to absorb heat from the interior of the refrig-erator or freezer.
16 Because the refrigerant flows in a closed system, 17 and the actual rate of flow through the capillary tube is 18 dependent upon the pressure differential between the pres-19 sures in the condenser and the evaporator, any change in load conditions will affect the operation of the system. In the 21 case of refrigerators and freezers, the changes in operating 22 conditions can result from changes in the room ambient 23 temperature, which affects the heat dissipation from the 24 condenser, as well as the internal conditions, which may be determined by the opening and closing of the door and the 26 addition of warm items to affect the load on the evaporator.
27 Furthermore, because the system must operate on a cyclic 28 basis to maintain reserve capacity for extreme conditions, 29 a thermostat inside the refrigerator causes the compressor to cycle on and off, and when the compressor is off, the 31 pressure tends to equalize throughout the system, resulting 32 in the elimination of liquid refrigerant in the capillary 33 tube, which then becomes entirely filled with gas. The 34 result of these changes in operating condition is that the 1 refrigeration system is often operating under conditions - 2 other than optimum with regard to the temperatures and 3 pressures in the condenser and the evaporator, causing a loss 4 of energy efficiency in the system.
Some of these effects can be minimized in various 6 ways. For example, to minimize the formation of flash gas 7 in the capillary tube, which would tend to reduce the capaci-8 ty of the system, the tube is usually soldered or otherwise 9 placed in heat transfer relationship with the return line from the evaporator to the compressor. Because the common 11 optimum conditions are such where the system operates at say 12 a fifty percent duty cycle, the capillary tube is usually 13 sized "loose" or with a reduced restriction which allows fast 14 flooding of the evaporator during start-up and fast equaliza-tion of suction and discharge pressure during the OFF portion 16 of the cycle.
17 The fast flooding of the evaporator allows the 18 system to quickly reach a high running efficiency, thereby 19 réducing the total compressor run time for the ON cycle.
Once the evaporator is flooded, however, this type of system 21 tends to allow gas to enter the capillary tube and pass 22 directly into the evaporator. When gas passes from the 23 condenser to the evaporator, it never goes through the phase 24 change to a liquid and back to gas that is necessary to produce effective cooling in the evaporator. Not only does 26 this load the compressor with an increased mass flow that 27 does not refrigerate, but it also transports heat into the 28 evaporator, to thereby reduce the efficiency of the system.
29 When the compressor is turned off at the end of the run cycle, the pressure equalizes between the condenser and the 31 evaporator across the capillary tube relatively quickly, and 32 this allows hot gas and liquid to pass into the evaporator.
33 This adds heat to the evaporator and decreases overall system 34 efficiency. The fast equalization, however, allows a lower -1 cost, split phase compressor motor, with its relatively low 2 starting torque, to restart after a short OFF cycle.
3 On the other hand, if the system uses a "tight~ or 4 more restrictive capillary tube, the system will tend to have a slightly greater efficiency during steady state run condi-6 tions, but the evaporator floods so slowly during start-up 7 that the advantage in efficiency may be lost over the entire 8 run cycle. Furthermore, equalization may take so long that 9 the compressor may have starting difficulties with a short OFF cycle because the low starting torque is unable to 11 overcome the remaining back pressure in the condenser.
12 In larger refrigeration systems, these problems are 13 overcome by using a controlled expansion valve as the re-14 striction instead of the capillary tube. Valves of this type generally use a diaphragm or bellows operated by a refriger-16 ant bulb that senses the temperature at some point in the 17 system and opens or closes the valve located at the evapora-18 tor inlet to vary the amount of restriction at this point.
19 For example, Owens U.S. patent No, 3,367,130 discloses an expansion valve which opens and closes in response to the 21 amount of subcooling of the refrigerant leaving the condens-22 er by responding to a sensor attached to the external surface 23 of the tube at that point, which as disclosed is remote from 24 the valve itself. However, valves of this type are too large and much too expensive to be substituted for a capillary tube 26 in small refrigeration systems.
27 In the completely different area of refrigeration 28 for automotive air conditioning, it has been proposed to 29 provide a subcooling flow control valve to control refriger-3~ ant flow to the evaporator in conjunction with an additional 31 downstream flow restrictor, such as an orifice. European 32 Patent Publication No. 255,035, published February 3, 1988, 33 shows a flow control valve with an external bulb used in an 34 automotive air conditioner with a downstream restriction that 1 may be a capillary or an orifice. U.S. patents Nos.
2 4,788,828 and 4,840.038, both in the name of Motoharu Sato, 3 both disclose control valves using an internal sealed bellows 4 filled with a refrigerant for controlling flow to a down-stream restriction in an automotive air conditioning system.
6 The first of these patents shows a bleed passage bypassing 7 the valve to allow equalization when the compressor is turned 8 off. The second patent uses a second bellows downstream of 9 the valve to expand and force open the valve closed by the first bellows, to allow equalization to take place across the 11 valve. All of these arrangements are intended for automotive 12 air conditioning where the engine provides sufficient power 13 for the compressor under all conditions, and the purpose of 14 the valve is to regulate flow under a wide range of flow rates resulting from widely varying engine, and hence com-16 pressor, speeds.

18 The present invention provides an improved and more 19 efficient refrigeration system for household refrigerators and freezers using a capillary tube restriction by adding a 21 novel subcooling flow control valve between the condenser 22 outlet and the entrance end of the capillary tube.
23 The flow control valve is an internally self-24 contained unit which modulates the flow proportional to the amount of subcooling in the refrigerant flowing through the 26 valve. The valve is set to close completely when the amount 27 of subco~ling is reduced below a minimum specified positive 28 value, and will remain closed when the compressor is turned 29 off to prevent equalization of the system and any flow of hot refrigerant into the evaporator. When the compressor starts, 31 it must discharge into a condenser that is already at an 1 elevated pressure because of the lack of e~ualization across 2 the flow control valve. Although this pressure will have 3 dropped below the normal operating pressure of the condenser 4 as a result of cooling of the condenser during the OFF cycle, the compressor still requires a high starting torque motor 6 but not one with a higher horsepower rating for run condi-7 tions. Higher starting torque can be provided by the use of 8 a capacitor start motor. After the compressor restarts, the 9 pressure in the condenser will rise until a subcooled liquid is present at the outlet. When the liquid at the outlet 11 reaches the predetermined minimum specified positive subcool-12 ing value, the flow control valve will begin to open and 13 allow refrigerant to flow to the capillary tube, and hence 14 into the evaporator. The flow control valve provides in-creased flow as the amount of subcooling increases, and such 16 increased flow will allow desirable flooding of the evapora-17 tor.
18 In this system, the capillary tube is sized as a 19 significantly looser or less restrictive tube, and the pressure drop will be less than normal, with the rest of the 21 drop taking place across the flow control valve. Thus, the 22 pressure drop across the capillary tube will remain propor-23 tional to the mass flow rate of the refrigerant, while the 24 pressure drop across the flow control valve will be inversely proportional to the mass flow rate, since the valve opens 26 more with increased mass flow which tends to be proportional 27 to the amount of subcooling of the refrigerant at the outlet 28 of the condenser. Since the flow control valve will close 29 before the amount of subcooling at the condenser outlet drops below the minimum specified value, at no time during the 31 cycle of operation of the system will gas enter the capillary 32 tube.
33 The flow control valve is a self-contained unit 34 which is responsive to the subcooling of the refrigerant 1 actually flowing through the valve. According to the pre-2 ferred embodiment of the valve, the housing has an inlet 3 connected to the outlet of the condenser and an outlet 4 connected to the inlet end of the capillary tube, leading in turn to the evaporator, and this housing defines a first 6 chamber between the inlet and the outlet. A movable wall 7 member in the form of a sealed bellows is mounted in this 8 first chamber between the inlet and outlet. The portion or 9 end adjacent the inlet is fixed with respect to the housing, while the opposite or movable portion or end carries a valve 11 element. A valve seat is mounted on the housing adjacent the 12 outlet and is engageable by the valve element to seal and 13 prevent any flow of refrigerant from the inlet to the outlet 14 when the valve is fully closed. The interior of the bellows defines a second chamber which is filled with a refrigerant 16 in a saturated state, and the refrigerant may be either the 17 same as that in the system or a fluid which has a greater 18 saturation pressure than that of the refrigerant in the 19 system. To allow better response, the second chamber in-cludes a tubular portion extending back into the inlet tube 21 and exposed to the incoming refrigerant to ensure the most 22 effective heat transfer between the system refrigerant and 23 that in the second chamber, so that the second refrigerant 24 and temperature will closely track that in the first chamber.
The minimum specified subcooling value or set point 26 must be selected to be high enough in terms of the subcooling 27 pressure in the surrounding refrigerant in the first chamber 28 to ensure that the valve never opens unless there is a 29 subcooled liquid in the first chamber and always closes before any gas can enter the capillary tube. On the other 31 hand, the set point cannot be too high or there will be 32 difficulty in promoting the initial flow as the valve opens 33 after the system has started.

2 FIG. 1 is a schematic representation of a 3 refrigeration system incorporating a flow control valve 4 constructed according to the present invention;

FIG. 2 is a cross-sectional view of one preferred 6 flow control valve constructed according to the present 7 invention; and 8 FIG. 3 is a cross-sectional view of another pre-9 ferred flow control valve constructed according to the present invention.

12 Referring now to the drawings in greater detail, 13 FIG. 1 is a schematic illustration of a vapor compression 14 refrigeration system 10 which is typically used in the household refrigerator or freezer. The system 10 includes 16 an electric motor-driven compressor 12, preferably of the 17 hermetic type, having an output connected to a condenser 14, 18 and an evaporator 16 which is mounted inside of an insulated 19 compartment 22 and the return from the evaporator 16 is connected back to the inlet of the compressor 12. This 21 system is a closed recirculating system filled with a suit-22 able refrigerant such as R12 and, to provide the necessary 23 flow restriction between the condenser 14 and the evaporator Z4 16, typically a capillary tube 18 is used as the expansion controlling device. While not shown in FIG. 1, typically the 26 capillary tube 18, which is carefully sized to a given-1 internal diameter and length, is connected in heat conducting2 contact with the line between the compressor 12 and the 3 condenser 14. In accordance with the present invention, a 4 control valve 20 is connected in the line between the con-denser 14 and the entrance end of capillary tube 18.
6 In order to maintain the compartment 22 at desired 7 temperature, a suitable thermostat 19 is provided to operate 8 responsive to a sensing bulb 21 placed within the compartment 9 22 to sense its temperature. The thermostat 19 operates through electrical contacts which connect or disconnect the 11 electrical supply from supply lines 23 to the electric motor -12 driving the compressor 12. Thus, when the temperature sensed 13 by the bulb 21 rises to a predetermined level as the result 14 of heat influx into the compartment 22, the contacts in thermostat 19 will close to energize the compressor 12 for 16 a length of time until the compartment 22 drops to a lower 17 temperature, which allows the thermostat 19 and compressor 18 12 to cycle off until the temperature again rises to the 19 predetermined level.
It will be understood that the length of time that 21 the compressor 12 is running, the duty cycle, depends upon 22 the ambient temperature surrounding the compartment 22, and 23 the other components of the system, as well as other factors 24 such as the thermal mass inside the compartment 22 and the number of times any access door is opened and closed to allow 26 admission of the warmer external air. Thus, under most 27 conditions, the system is sized so that the compressor will 28 have a duty cycle or run time of approximately fifty percent, 29 but this can rise, particularly when door openings and closings occur often or there is a high ambient temperature.
31 Likewise, if the refrigerator or freezer is placed where the 32 ambient temperature is low, the duty cycle may be much lower.
33 One embodiment of the control valve 20 is shown 34 schematically in FIG. 2 in longitudinal cross section. The 1 valve 20 includes a short tubular valve housing 26 having an 2 inlet fitting 28 welded or soldered to one end and defining 3 a reduced diameter inlet opening 29 which is connected to the 4 tubing from the condenser 14. At the other end is an outlet fitting 30 which may be similar to inlet fitting 28 and has 6 a reduced outlet opening 31 which is, in turn, connected by 7 a suitable fitting to the inlet end of the capillary tube 18.
8 The internal mechanism for the control valve 20 is 9 shown in generally schematic arrangement, and includes an inlet plate 32 extending across the inlet side of the housing 11 26 and having a plurality of inlet openings 33 extending 12 therethrough and providing sufficient area to allow free flow 13 of the refrigerant from the inlet fitting 28 into the interi-14 or chamber 36 of housing 26. At the other end, the chamber 36 is closed off by an outlet plate 34 extending across the 16 housing 26 in sealing relation and defining a valve seat 35 17 at its central opening in coaxial alignment with the inlet 18 fitting 28 and the outlet fitting 30.
19 Thus, a first chamber 36 is defined by the valve housing 26 and the two plates 32 and 34, and the operating 21 valve mechanism is located in this chamber. A boss 38 is 22 formed on the side of inlet plate 32 within chamber 36, and 23 serves as a seat for one end of an elongated bellows 40, 24 whose other end is closed off by a base 43 of valve member 42, which in turn has a tip 46 adapted to engage the valve 26 seat 35. The bellows 40 is designed to allow free longitudi-27 nal expansion so that the valve member 42 can move axially 28 within the chamber 36 in a direction toward and away from the 29 valve seat 35 carried on outlet plate 34. Thus, the bellows 40 defines within itself a second chamber 44 which is com-31 pletely sealed from the first chamber 36, and is filled with 32 a calibrated charge of a suitable refrigerant, which may be 33 either the same refrigerant as is used in the system, such 34 as R12, or one having a higher vapor pressure at the same ll 1 temperature under saturated conditions, such as R500. The 2 amount of this change is calibrated to ensure that the valve 3 is completely closed as long as the conditions in the first 4 chamber are such that the amount of subcooling of the system refrigerant is below a predetermined minimum value or set 6 point. Only when the subcooling exceeds the set point does 7 the valve open to allow subcooled liquid refrigerant to enter 8 the capillary.
9 It should be noted that a tubular portion 48 projects from the boss 38 and is engageable by the valve 11 member base 43 under extremely low temperature conditions to 12 limit the movement of the valve member 42 away from the 13 outlet plate 34. An extension tube 49 is mounted within the 14 tubular portion 48 and extends back through the inlet opening 29, where it is sealed and, therefore, made a part of the 16 second chamber 44. The extension tube 49, by extending back 17 through the inlet, is in thermal transfer contact with the 18 incoming refrigerant to ensure that the temperature of the 19 refrigerant within the second chamber 44 will track as closely as possible the temperature of the incoming system 21 refrigerant, to ensure a minimum of delay in response time 22 of the valve. It should also be noted that the valve member 23 tip 46, which extends through the valve seat 35, may be 24 configured to provide a varying orifice size with the valve seat 35 as the valve member 42 moves to different axial 26 positions in response to pressure and temperature changes 27 within the valve.
28 When the compressor 12 is off and has not been run 29 for some time, the valve 20 is closed, with the valve member tip 46 in tight engagement with the valve seat 35 to posi-31 tively prevent any flow of refrigerant from the inlet to the 32 outlet, and hence from the condenser to the evaporator. When 33 the compressor is started after an OFF cycle, it pumps 34 residual refrigerant out of the evaporator and into the 1 condenser to cause an increase in pressure within the 2 condenser. Since the refrigerant at the outlet of the 3 condenser is already at a relatively cool temperature, the 4 increase in pressure which is reflected throughout the condenser results in a sub-cooling of the refrigerant at the 6 condenser outlet and inlet to the control valve 20. This 7 pressure increase will act on the refrigerant within the 8 chamber 44, which will be retained at the same low subcooling 9 temperature as the incoming refrigerant, causing the volume within the chamber 44 to decrease. This will cause the 11 bellows 40 to shrink and move the valve member 42 toward the 12 inlet so that the valve member tip 46 moves away from the 13 valve seat 35 and the valve opens to allow refrigerant to 14 begin to flow into the capillary, and hence to the evapora-tor. When the compressor initially starts, the opening of 16 the valve member 42 will tend to be somewhat gradual, and 17 there will be a substantial pressure drop across the valve 18 so that only a portion of the total pressure drop between the 19 condenser and evaporator will occur across the capillary tube 18. As the valve member 42 moves farther away from valve 21 seat 35, the resultant drop in restriction will decrease ~he 22 pressure drop across the control valve 20 and increase the 23 pressure drop across the capillary tube 18, and the total 24 mass flow of refrigerant will increase In cases where the evaporator may have warmed up to a temperature substantially 26 above the normal operating temperature, as would be the case 27 in a frost-free refrigerator or freezer after a defrost cycle 28 in which the evaporator had been additionally heated by an 29 electric defrost heater, the rate of flow of refrigerant will be at a maximum and the valve 20 will be at a substantially 31 wide open position, so that substantially all of the pressure 32 drop takes place across the capillary tube 18, and the 33 capillary tube must be sized to allow this flow under these 34 conditions.

-1 As the compressor continues running during the ON
2 cycle, the refrigerated compartment 22 will continue to cool 3 and the temperature of the evaporator 16 will likewise drop.
4 Thus, there is a drop in the total mass flow of refrigerant and the subcooling at the outlet of the condenser 14 will 6 decrease and the valve member 42 tend to move closer to a 7 closed condition. However, the valve will remain open as 8 long as the subcooling condition exists at the condenser 9 outlet.
When the compressor 12 stops for any reason, such 11 as by operation of the thermostat 19 detecting a minimum 12 temperature in the chamber 22, there is no longer any flow 13 of refrigerant into the condenser 14 and the pressure at the 14 outlet will tend to rise as liquid refrigerant continues the flow through the valve 20 and into the capillary tube 18.
16 However, as soon as the pressure reaches a set point which 17 is still within the subcooling range, the valve member 42 18 will close so that the tip 46 seals off the valve seat 35-to 19 prevent any further flow of refrigerant from the condenser to the evaporator. This ensures that no vapor will enter the 21 evaporator, and prevents heat from being transferred from the 22 condenser to the evaporator as long as the compressor is on 23 the OFF cycle. Since vapor entering the evaporator as a 24 result of the refrigerant's being above the subcooling threshold would decrease the efficiency of the system, the 26 prevention of refrigerant flow during the OFF cycle prevents 27 the heating of the evaporator, and hence the compartment 22, 28 that would otherwise occur if the valve 20 were not present.
29 Although the pressure within the condenser will continue to drop from cooling of the refrigerant during the 31 compressor OFF cycle, there will still tend to be a substan-32 tial back pressure at the discharge side of the compressor 33 when it restarts at the beginning of the next ON cycle, and 34 this back pressure will require substantially higher starting 1 tor~ue from the compressor motor than would otherwise be 2 required if the pressure were allowed to equalize between the 3 condenser and evaporator. This can be overcome by using a 4 high starting torque electric motor for the compressor, and it has been found that the use of capacitor start motors for 6 the compressor will easily provide sufficient starting torque 7 that restarting of the compressor will not be a problem.
8 After the compressor restarts, because of the 9 pressure differential between the condenser and evaporator as a result of valve 20 being closed, running conditions are 11 more quickly re-established than if the pressure had equal-12 ized. The evaporator is reflooded more quickly, thus result-13 ing in a decrease of the run time of the compressor for a 14 given amount of cooling during the ON cycle.
Another embodiment of the control valve is shown 16 at 58 in FIG. 3, and it will be understood that this valve 17 is located in the system shown in FIG. 1 in the same position 18 as control valve 20. This control valve includes a housing 19 60 comprising cup-shaped inlet and outlet members 61 and 62, each having peripheral flanges 63 and 64. Within the housing 21 60 is located a transverse partition member 65, also having 22 a peripheral flange 66 which is clamped between the flanges 23 63 and 64 in the form of a sandwich, which may then be brazed 24 and welded around its periphery to provide a unitized sealed housing 60. The inlet member 61 is provided with a central 26 inlet fitting 67 which is connected to the condenser 14, 27 while the lower or outlet member 62 is provided with an 28 outlet fitting 68, which in turn is connected to the capil-29 lary tube 18. Then, as control valve 58 is located in the system, it is preferably positioned so that the inlet fitting 31 67 is uppermost and the axial alignment between the fittings 32 67 and 68 is substantially vertical. The valve should be 33 located at a generally low point in the system to ensure 1 positive liquid flow from the condenser 14 into the inlet 2 fitting 67.
3 The partition member 65 separates the interior of 4 housing 60 into an inlet chamber 71 between the inlet member 61 and partition 65 and an outlet chamber 72 between the 6 partition 65 and the outlet member 62. Within the inlet 7 chamber 71, a support plate 74 is positioned a spaced dis-8 tance from the partition 65 and has an outer peripheral edge 9 76 which is secured by welding or brazing to the flange 66 and partition 65 within the inlet chamber 71. The support 11 plate 74 has a plurality of openings 77 therein to ensure 12 free fluid communication within the chamber 71 on both sides 13 of the support plate 74.
14 Between support plate 74 and partition 65 is lS located a movable wall member in the form of upper and lower 16 diaphragm members 81 and 82, which are sealed together around 17 the edges 83 and define a chamber 80 between them. The upper 18 diaphragm member 81 is stationary with respect to the support 19 plate 74, while the lower or movable diaphragm or wall member 82 carries on its lower side a cup 84 secured thereto by 21 welding or brazing, and carrying a valve seal 86 which may 22 be formed of a suitable resilient material such as polytetra-23 fluoroethylene or a suitable rubberlike elastic material 24 which is fully compatible with the refrigerant of the system.
The valve seal 86, in turn, is adapted to make contact with 26 the valve seat 87 formed around opening 88 extending through 27 the partition member 65 and providing the sole communication 28 between the inlet chamber 71 and the outlet chamber 72. If 29 it is so desired, the cup 84 or other members can be config-ured to engage the partition 65 to limit travel of the cup 31 84 and seal 86 against the valve seat 87 to minimize the 32 effects of cold flow or set on the material forming the 33 seal 86.

1 To secure the upper diaphragm member 81 in posi-2 tion, it is secured to a flange 91 on a fitting 90, with the 3 flange 91 also being held in position against the lower side 4 of support plate 74 by a bead 92 formed on the fitting 90 above the support plate 94. The upper end of fitting 90 is 6 formed with an open end 94, where it is sealingly secured to 7 the end of a tube 95 which extends upwardly through the inlet 8 fitting 67. At its lower end, tube 95 makes a sealing fit 9 against an opening 96 in the upper diaphragm member 81, so that the interiors of tube 95 and chamber 80 are in full 11 fluid communication but sealed from the inlet and outlet 12 chambers 71 and 72. Thus, the chamber 80 is filled with a 13 second refrigerant in a saturated condition in the same 14 manner as second chamber 44 of control valve 20.
It will thus be seen that the valve of FIG. 3 16 operates in the same manner as the valve of FIG. 2, in that 17 as long as the conditions of the fluid within the inlet 18 chamber 71 and inlet fitting 67 are at temperatures and 19 pressures above a subcooling level, the valve seal 86 will be in tight engagement with the valve seat 87 to prevent 21 fluid communication between the inlet and outlet chambers 71 22 and 72, and hence prevent any flow through the valve. As 23 soon as a subcooling condition exists when the system is in 24 operation, such subcooling will reduce the temperature and/
or increase the pressure within the inlet chamber 71, and 26 hence the second chamber 80, and the result will allow the 27 valve seal 86 to move away from the valve seat 87 so that 28 refrigerant will flow through the valve in the same manner 29 as described above.
Although several preferred embodiments of the 31 invention have been shown and described in detail, it is 32 recognized that various modifications and rearrangements may 33 be resorted to without departing from the scope of the 34 invention as defined in the claims.

Claims (2)

1. A refrigerated cabinet comprising a compartment in said cabinet, a compressor and a condenser mounted on said cabinet, an evaporator in said compartment, a capillary tube connecting said evaporator and said condenser in a closed circuit containing a first refrigerant, a thermostat responsive to the temperature in said compartment for selectively energizing said compressor to maintain the temperature in said compartment within a predetermined range, a flow control valve between said condenser and said capillary tube, said flow control valve having a housing defining a first chamber, an inlet to said first chamber connected to said condenser, and outlet from said first chamber to said capillary tube, said housing being mounted on said cabinet at a low point in the system with said inlet and said outlet fittings being in substantially vertical alignment to insure that only a subcooled liquid flows to said inlet, a valve seat on said housing at said outlet, a moveable wall member within said first chamber defining a second chamber, said movable wall member being secured to said housing, a valve member operable by movement of said movable wall member to move to and from said valve seat, said second chamber being filled with a predetermined saturated charge of a second refrigerant whereby said valve member is spaced from said valve seat when the subcooling of said first refrigerant in said first chamber is greater than a predetermined amount and said valve member is moved into engagement with said valve seat when the subcooling of said refrigerant in said first chamber is less than said predetermined amount, engagement of said valve member with said valve seat preventing any flow of said first refrigerant from said inlet to said outlet.

2. A refrigerated cabinet as set forth in claim 1, wherein a portion of said second chamber is in an extension tube extending upward through said inlet toward said condenser.