US3449923A - Refrigerant feed control and systems - Google Patents

Description

June 17, 1969 c. c. HANSEN ETAL 3,449,923

REFRIGERANT FEED CONTROL AND SYSTEMS Filed March 8, 1968 Sheet of 2 High Flow INVENTORS m CHARLES c. HANSEN KENNETH H. MAUER 5mg 3 OLAF E. KIVIOJ Supply Pressure p.s.i y

FIG. 5

Liquid Uni's June 17, 1969 c. c. HANSEN ET AL 3,449,923

REFRIGERANT FEED CONTROL AND SYSTEMS Filed March a, 1968 I Sheet 2, of 2 INVENTORS CHARLES c. HANSEN KENNETH H. MAUER F l Wffl/(VIOZA ATTY' S United States Patent 3,449,923 REFRIGERANT FEED CONTROL AND SYSTEMS Charles C. Hansen, Hinsdale, Kenneth H. Mauer, Roselle, and 0laf E. Kivioja, Villa Park, Ill., assignors to Refrigerating Specialties Company, Broadview, 11]., a corporation of Illinois 'Continuation-in-part of application Ser. No. 627,715, Apr. 3, 1967. This application Mar. 8, 1968, Ser. No. 720,431

Int. Cl. F25b 41/04, 43/00; F16k 31/12 US. Cl. 62-217 15 Claims ABSTRACT OF THE DISCLOSURE A refrigeration system in which a variable fiow rate balance valve ahead of an evaporator chamber is unaffected by pressure variations in a flooded refrigerant supply line at its inlet, but is controlled as to its fiow rate opening by downstream pressure of fluid flowing from it and through a manually adjustable orifice valve to maintain a selected constant refrigerant pressure in the evaporator chamber.

Cross-reference to related application This application is a continuation-in-part of application Ser. No. 627,715, filed Apr. 3, 1967 and now abandoned.

Background of the invention The present invention relates generally to refrigerant feed controls in systems handling fluids in their liquid phase and has particular application to refrigerant recirculating systems having one or more low pressure evaporating liquid circuits.

Such systems include dry expansion and flooded evaporators, preferably arranged in parallel between liquid refrigerant supply and vapor return lines, and contemplates single or multi-temperature evaporators, single and multiple compressors, one or more condensors and a common surge tank means from which liquid refrigerant is supplied to the supply line.

Such systems are generally characterized by a surge tank which receives both expanded refrigerant from the return line and liquefied refrigerant from the condenser. Between the tank and condenser a compressor is connected to take vapor from the surge tank, compress it and discharge it to the condenser at high pressure where it liquefied. Valve means such a a float valve is provided to supply and maintain a substantially constant level of liquiefied refrigerant in the surge tank at the low compressor suction pressure and a pump is used to hydraulically drive liquid refrigerant from the tank through the supply line to the inlets of the evaporator coils. The present invention is primarily concerned with the flow and control of liquid refrigerant to and through the individual evaporators.

The evaporators may be of many different but frequently used varieties and may be located at various locations widely spaced in a refrigerating plant on the same and different floors, it being appreciated that the circuits will further ditfer in passage areas, flow distances, elevation and refrigeration load, to the end that the effective inlet pressures of the evaporators not only vary quite widely with respect to one another but also vary individually from time to time during their work cycles. Furthermore, individual evaporator circuits can be differently equipped, some with pressure regulators at the evaporator outlet in addition to expansion valves at the inlet to maintain a constant temperature or pressure in the evaporators. Automatic valves for different cycles, and composite load peaks all further vary the supply pressure at the evaporator inlets.

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Accordingly, there will tend to be great differences in the amount of re-circulating liquid which will tend to flow through each of the various evaporators in the various locations. Thus, some evaporators will receive too much liquid refrigerant and others will receive too little. The commonly accepted method of correcting for liquid flow disparity is manually set balancing valves in the inlet to each evaporator having relatively small orifices, needle valves or fixed orifices.

However, with this expedient there is a constant adjustment of the valves because with a change at one valve a flow change with the others is engendered, and to combat this pressure regulators are permanently installed or temporarily used and calibration equations have to be determined and empirically checked from time to time.

For complete adjustment of a plant many trial adjustments are necessary and when other flow control equipment varies its functions, the discrepancies again reappear, particularly where fiow is controlled by inlet solenoid or similarly functioning valves. Other cycling systems are employed but none are able to control evaporator pressure variations which occur with pressure variations in the suction line.

Summary of the invention The present invention overcomes these difficulties by the creation and use of an evaporator feed control in each evaporator circuit. All circuits are quickly adjusted any time to receive optimum liquid supply without assistance of pressure gauges, and pressure changes throughout a wide range short of emergency conditions do not materially alfect the liquid flow desired for each evaporator circuit with, or without, the use of other flow controls conventionally employed.

Two flow control valves arranged in series flow relationship control the fiow of liquid refrigerant to the evapo rator through a first conduit from a supply header, one as set by hand and the other controlled by the pressure differential across the hand set valve through another conduit interconnecting the header and evaporator. The valves open in the direction of flow in the one conduit and a pressure responsive means in the other conduit controls one of the valves and operates as a back fiow check valve for the other conduit while the other valve operates as a back flow check valve for the first conduit.

An object of the invention is to over-supply all evaporator circuits in a predetermined constant ratio which safely includes maximum expected load conditions of the circuits involved.

A further object of the invention is to provide a forward feed at a predetermined ratio irrespective of pressure changes yet instantly prevent any backflow under any adverse conditions or alternate operating conditions such as defrosting.

The invention is characterized by a balanced variable flow-control valve responsive to the differential pressure across a manually adjusted flow area and is substantially unaffected positionally by supply pressure variation, particularly when the outlet pressure is kept constant in the system.

Further characteristics include a manually adjusted readily assembled indicator knob with a lineal flow adjustment scale protected against frosting; an arrangement which freely drains itself to eliminate sludge buildup, and structure materials are compatible to minimize leakage area differences and binding of the balanced valve in its operation.

This invention makes it possible to design and erect refrigeration systems with multi-evaporators using the re-circulation method, which are considerably easier to put into operation, less costly to maintain, and provide ease of manufacturing and holding tolerances, and rapidity of assembly and testing including replacement of control spring or substitution of a variable control thereof will become apparent from the following description and the drawings, in which:

FIG. 1 is a diagrammatical representation of a typical system improved in its performance by and as a part of the present invention;

FIG. 2 is a vertical sectional view of the liquid feed control for a liquefied gas embodying the invention;

FIG. 3 is a fragmentary view of a portion of the control shown in FIG. 2 illustrating a modification of the invention;

FIG. 4 is an enlarged fragmentary view of the valve seating structure on a control element shown in FIGS. 2 and 3;

FIG, 5 is a graphical representation of the operation of the control shown in FIG. 2 in a typical system such as shown in FIG. 1; and

FIG. 6 is a sectional view similar to FIG. 2 showing another modification of the invention.

Referring now to the drawing and particularly FIG. 1, a liquid re-circulating refrigeration system is shown in which a compressor 96 draws gas at suction pressure through line 95 from the top of surge tank 90, compresses it and discharges high pressure refrigerant gas through a conduit into a condensor 98 where the hot gas is cooled by means of a cooling fluid source 100 and is converted to a liquid refrigerant which flows into a liquid line 101 equipped with a volumetric receiver type of pressure vessel 90. From the high pressure liquid line 101, the liquid passes through a pressure reducing device such as a float valve 92 and enters a surge tank 90 at a pressure which is maintained at a level approximately equal to the suction pressure of gas entering the compressor 96 through line 95. Normally, the liquid level in the surge tank is maintained by the float valve or by a float switch and solenoid valve at a desired level 93 of liquid in the surge drum. This level is maintained normally sufiiciently below the suction gas exit 95 from the surge drum to prevent carryover of entrained liquid refrigerant into the compressor suction. Likewise, the liquid level 93 is maintained high enough to ensure an adequate supply of liquid and an adequate head of liquid for a liquid re-circulating pump 94, which is used to feed the cold liquid refrigerant out through the supply line into the plant where it can be directed toward one or several of many evaporators.

These evaporators may be of many different varieties and in many different locations in the plant. Some evaporators 11 may be on the first floor, others may be of a single pipe variety, a coiled type variety, a thin coil, a shell and tube pressure vessel, or any of the many different types of evaporators that are frequentl used. Some of these evaporators may have very short refrigerant flow circuits with generous passage areas for the refrigerant gas resulting in a very low or even negiligible pressure drop as a refrigerant gas passes through the evaporator. On the other hand, some evaporators 11 may have very long and restrictive circuits which result in relatively high pressure drop as the refrigerant passes through the evaporator.

The representative system utilizing the invention as shown in FIG. 1 shows three different but representative types of evaporator circuits. The liquid refrigerant supply line is shown at 80 and the suction line is shown as 82.

The upper circuit 84 includes the feed control valve 10, the evaporator coil 11 and an evaporator pressure regulator 13 connected in series between the supply line and the suction line. A shut-off valve 17, preferably controlled by a thermal responsive device such as a thermal bulb (not shown) .actuating a solenoid which controls liquid to flow or not flow through the liquid valve 10 whether connected thereto at the inlet 18 or outlet 55 of the valve 10. In this circuit the pressure at the outlet 55 is substantially constant as controlled by the evaporator pressure outlet regulator 13, and irrespective of supply line pressure the feed control 10 will deliver liquid refrigerant, at whatever flow rate required, at a pressure that is in excess of the evaporator set pressure. This stabilized flow being constant such improves the performance and control effect of the pressure valve 13. V

In the next evaporator circuit 86 the feed control 10 is connected in series with .an off-and-on solenoid valve 21 remotely controlled, .and the evaporator 11, between the liquid supply line and suction line 82. Here the evaporator coil is at suction pressure and when the .solenoid valve is open the feed control 10 operates to increase refrigerant flow with an evaporator pressure rise.

Referring now to FIG. 2 showing a preferred embodirnent of the feed control 10 in its closed down condition, a two-piece housing is shown comprising a main body member 12 and a cap member 14 suitably secured together by bolts 15 as marginally sealed by a tonguegasket-groove joint 16. An inlet passage 18 and an outlet passage 55 are connected by two separate conduits formed in the body member 12 which bifurcate from a valve chamber 20 with oppositely opening valve guide cylindrical surfaces 22 and 32 that are held to close tolerances. The cylindrical surfaces terminate outwardly in valve ports 24 and 25 respectively. Beyond the valve ports, enlarged valve compartments 26 and 27 are provided, the lower one 26 ending in a threaded access opening 28 that is closed by a male plug 30 having a boss 31 on its upper end, and the upper one 27 ending in a reduced cylindrical valve guide opening 32 that terminates in an upwardly facing valve seat 33 on the upper face of the body member 12.

A piston element 36 is reciprocably disposed in the cylindrical surface 22 with close clearance and has on its lower end .an enlarged head 27 defining a valve element 38 that closes against the port 24 as urged by a compres- S1011 spring 40 carried by the boss 31. At the upper end a piston rod 4.1 serves as a valve stem for a flow control sleeve valve 46 cooperating with the upper valve port 25. The sleeve portion is provided with triangular castellatrons 44 and is reciprocably carried by a valve head portlon 46 secured to the upper end of the stem rod 41. The upper valve 46 is fully open when the lower valve 1s fully closed.

A sleeve valve 48 also having a multi-slot castellated gulde sleeve 49 for multiple lineal orifice flow control reclprocates in the guide opening 32 and serves also as a backfiow check valve in its closed position as urged by the compression spring 50. The sleeve valve 48 is adustably limited to its open position by a stop element 52 carried by the cap 14.

An outlet conduit 54 is provided opening coplanar with the valve seat 33 and opens at its lower end into the outlet opening at 55 and is in communication through the connecting passage 56 with the valve compartment 26. The lower end of the cap member 14 has a cavity 47 therein which places the valve seat 33 in sealed commumcatlon with the passage 54.

The stop element 52 is threaded to the cap and has a stem 58 which extends upwardly through the cap 14 where it is journalled in flange 59 and sealed by a packmg 60 that is compressed by gland nut 61. The upper end of the stem is hollow to reduce its heat conductivity to the body 12 .and receives a press fitted knurled closure plug 62 at its upper end upon which is mounted a head 63 that is adjustably locked to the plug 62 by a set screw 64. A hex nut 65 is threaded on the head 63 to secure the upper flanged edge of a volume flow calibrated indicator sleeve 66 that covers the head. A sleeve 68 having sight slots 69 therein with .an indicia groove line 70 around it near its top is secured to the cap 72 over the stem so that the line 70 and calibrated indicia 67 on sleeve 66 cooperate to indicate the opening area permitted to the check valve 48 by the stop 52. A removable protective cap 72 closes the upper end of the sleeve after the stop 52 has been adjusted to the desired flow opening calibration of the valve 48. The fins 73 on the sleeve are cooling fins minimizing vaporization of refrigeration in the cavity 47 and frosting at cap 72.

In operation, with liquid refrigerant entering the inlet passage 18 under pressure, liquid, with balanced effect initially on the piston 36 and valve 46, flows through the triangular castellations 44 into compartment 27 and also presses down on piston 36 which quickly responds tending to close the valve 46 since there is no initial counter pressure in the outlet conduit 55 that is effective on the piston in compartment 26. However, once the valve 46 approaches its closed position, pressures equalize on the valve and piston and the spring 40 holds the valve 46 slightly open, same being preferably provided with a 2 p.s.i. differential pressure effect.

Thereupon the stop 52 is adjusted to the flow calibration selected and the liquid refrigerant entering the compartment 27 opens the valve 48 to its flow capacity limit determined by the stop 52. The outlet passage 54 fills and pressure builds up below the piston 36 and pressures tend to equalize on opposite sides of the piston permitting the spring 40 to determine the pressure differential drop maintained between the inlet and outlet across the fixed flow control valve 48 which constant pressure differential across the valve 48 will maintain a substantially constant volume flow independent of the back pressure of the evaporator circuit at the outlet 55 and this is irrespective of pressure variations in the inlet passage 18, the adjustment of valve 48 thereby being the ultimate flow control.

A modification of the construction just described is shown in FIG. 3, in which the pressure below the piston is established through a conduit 56a directly from the cavity 47 independently of liquid flow effects of conduit 55a thereon that might be present in conduits 54 and 55 of FIG. 2. The length and size of the conduit 56a with static liquid therein provides a dampening effect upon any flow variation effects otherwise occurring in conduit 55 of FIG. 2.

Referring to FIG. 4 where the contours of the valve port 24 and valve seat element 38 are shown somewhat diagrammatically, it is to be observed that the taper 74 to the axis 75 of the valve port 24 is sharper, or less, than the taper 76 on the valve seat so that the closing contact is at a circle located radially where the taper surfaces of revolution geometrically intersect. This circle is spaced from the cylindrical surface 22 so that repeated closings of the valve will not distort and change the close clearance intended between the piston and the cylinder. This clearance is preferably .00015" to minimize forward flow liquid leakage therebetween yet prevent binding. The valve elements close at this contact circle to prevent any backflow liquid leakage at this point when the check valve 48 is closed by its spring 50'. Thus, the operation of the piston is closely determined for longevity and constancy of performance.

FIG. 5 shows the performance curves of the construction described with liquid units in gallons per minute as ordinates against pounds per square inch of the supply pressure as abscissas for both high and low flow rates. The different flow setting of the stop 52 is represented by the abscissas marked Flow Setting, as rated by the calibrator lines 67 on the indicator 66 against the reference line 70 on the sleeve 68 when the valve stop 52 is set. The pressure drop is substantially constant across the valve 48 as determined by the tension of the spring 40, as already explained.

It will be observed that the back seating of the piston over a port area is appreciably greater than the piston area. A fiow over-shoot upon start up after shut off is substantially eliminated with the long piston-cylinder overlap and the close clearances provided. A drop in pressure established in the valve compartment 26 permits the piston to throttle the valve 46 without the area differential between the cylinder 22 and valve port 24 being of signifi cance. Thereafter, as resumed flow brings up the pressure in compartment 26, the pressures on both sides of the piston re-establish the pressure control differential, it being noted that the supply pressure effective for opening the valve 46 is balanced by the same supply pressure on the piston urging closure of the valve, the effective crosssectional area of the piston rod 41 being equal for both. Thus, the throttling valve is drawn immediately to a 2 psi. working position and then gradually returned to its flow control position with respect to the flow permitted by the valve 48.

There is shown a gradual increase in the liquid units delivered as the supply pressure increases. This is due to the leakage past the piston indicating the importance of close clearances. However, this leakage factor can be interpolated by empirically locating the indicator lines 67 to reflect the percentage leakage to flow. Either the curve inclinations can be used as a computation base with an average supply pressure, or, an aver-age flow volume requirement used. The close similarity of the curves however indicate the wide adaptability of the feed control in the major number of multi-evaporator refrigerating systems.

A further modification is shown in FIG. 6 wherein the adjustably fixed flo-w control valve 48 is located ahead of, but close to the variable flow, differential pressure controlled valve so that the fiow control element having the greatest flow area and variability is the last valve in the liquid refrigerant flow path. This is desirable with some refrigerants which have a high volatility and are operating within a working range of pressures where there is a possibility of vaporization occurring in the conduit space between the valves that might disrupt liquid solid flow through the last valve.

In this embodiment the inlet passage 18a of the main body 1211 is in open communication to the upper face thereof where its ends in the cylindrical valve guide opening 32a that terminates in the upwardly facing valve seat 33 receiving the sleeve valve 48 cooperatively therein. The outlet passage 55a leads from the upper face of the main body 12a through a cylindrical valve guide port 25a that terminates in an outlet valve compartment 27a.

A second conduit 56a interconnecting the valve compartment 27a and the inlet passage 13a includes a cylindrical surface 22a that is of the same size as the size of the port 25a and is coaxial therewith. Below the cylindrical surface 2211 the second conduit is enlarged to form a valve compartment 26a having a valve seat land 24a around a valve port leading to the inlet 18a through passage 56a.

A piston element 36a is reciprocably disposed in the cylindrical surface 22a with close clearance and defines on its lower end a valve element 38a preferably of Teflon which closes against the port 24a. At the upper end a piston rod 41a carried by the piston element serves as a valve stem for the flow control sleeve valve 46a which cooperates with the valve port 25a. As noted, the sleeve valve 46a is provided with triangular castellations 44a disposed to coact with the lower edge of the cylindrical valve port as reciprocably carried by the rod 41a whereby the lower valve 38a is fully closed when the upper valve is fully open as urged by the compression spring 40a interengaging the cap portion 14a and the sleeve valve 46a.

Except for the interchange of the two sleeve valves of the embodiment shown in FIG. 2 and the adaptation of the lower housing to accommodate them side by side the operation of the modification shown in FIG. 6 is similar to that of FIG. 2. Thus, the pressure differential responsive valve maintains the pressure differential across the manually adjusted valve at a constant pressure differential.

In both embodiments, the valve sleeves and piston are preferably hardened and ground to close tolerances to retard erosion and similarly the cylindrical guide surfaces are preferably hardened and ground, or ballburnished, for the same reason.

'Referring again to FIG. 1, for the circuit 84, evaporator pressure is maintained constant by regulator 13. Thus, the outlet pressure of feed control 10 is constant but the pressure at inlet 18 may vary due to pumping supply pressure variations. Feed control 10 maintains constant liquid flow to the evaporator in spite of this inlet pressure variation.

For the next circuit 86, solenoid valve 21 is operated by an electric switch or thermostat (not shown) to admit or deny flow to this evaporator. When the solenoid valve is open, the pressure at the outlet 55 of flow control 10 will vary widely as the pressure in suction line 82 deviates due to changes in total system load on the comressor. In addition, as for circuit 84, the pressure at inlet 18 will also vary. Despite these variations in its inlet and outlet pressure flow control 10, once set, will maintain constant liquid refrigerant flow in spite of changing inlet or outlet pressures caused by such factors as pressure regulators or compensating devices, solenoid valve resistances at the entrance or exit of the evaporator, liquid traps in the suction lines, dirty strainers, orifices, temperature mod- .ulated valves, compressor unloader cycling, subcooling fluctuations, and the varying demands of the evaporator being fed or of other evaporators in the system.

What has been said also applies to circuit 88, which has no control devices other than flow control 10.

Thus it will be seen how this invention overcomes all of the problems mentioned by the creation and use for each evaporator circuit of an evaporator feed control. Within acceptable tolerable limits of error, this evaporator feed control and its method of use will permit each evaporator circuit to be quickly adjusted to receive the optimum quantity of re-circulated liquid supply without reference to pressure gauges during the adjusting procedure. In addition, the evaporator feed control will maintain this desired mass flow rate of liquid supply within tolerable limits in spite of very drastic changes in liquid supply pressure, evaporator pressure, evaporator pressure drop, evaporator load changes, suction line pressure drop changes, or suction pressure changes. In this way, each evaporator is supplied with the ideal quantity of re-circulating liquid.

If, for instance, an evaporator has been designed for a 3:1 re-circulation rate: that is, three times as much liquid is to be supplied to the evaporator as is evaporated by the evaporator at full load, the evaporator will continue to be supplied with this quantity of liquid despite changes in any of the variables mentioned previously. Likewise, if an evaporator has been designed for a 1.25 full load recirculation rate, this can be quickly adjusted and constant quantity rate maintained. Similarly, even a 10:1 full load re-circulation rate can be adjusted and constant quantity rate maintained. The means by which this flow rate is maintained constant has been described and it will be further observed that one overall benefit of this invention will be to permit systems to be designed at lower feed rates than have been hitherto possible. In the past, high re-circulation rates were invariably required in order to overcome the fact that many evaporators in the field were being supplied with an excess amount of liquid under conditions that could not be corrected except at great expense because of the ditficulty of determining which evaporators were over-feeding and the difficulty of readjusting these evaporators and the rest of the evaporators in the system after the problem was pinpointed.

To give an example of the operation of the evaporator feed control system, assume that an evaporator has a normal loading of 10 tons of refrigeration. If the desired recirculation rate is 2:1, then the evaporator feed control would be set for 20 tons. Within the limitation of the invention that the pressure drop available for the evaporator feed control must be a minimum of 2 p.s.i., the mass flow rate to the evaporator would be maintained within plus or minus 20%, at a quantity which would be twice as much liquid as required during normal full load conditions. Suppose that at the time the device is set, the liquid supply pressure is 32 pounds and the evaporator pressure is 25 pounds. This would be a pressure difference of 7 pounds per square inch across the evaporator feed control. If several other evaporators in the system had their flow interrupted by solenoid valves, the liquid supply pressure would rise perhaps to 38 pounds, resulting in a pressure drop across the evaporator feed control of 13 pounds per square inch. Yet, this invention would continue to maintain, within tolerable limits, a mass flow rate to the evaporator equivalent to two times the normal full load refrigeration effect requirement.

In another situation, the liquid supply pressure may be 32 pounds and the evaporator pressure maintained at 25 pounds by a variable evaporator pressure regulator. If the evaporator pressure regulator is reset by an external control system to maintain 28 pounds per square inch evaporator pressure, then the pressure drop across the evaporator feed control, assuming no change in liquid supply pressure, would be 4 pounds per square inch. However, this invention would continue to maintain, under normal full load conditions, a re-circulation rate of 2:1. Similarly, if both the liquid supply pressure and the evaporator pressure varied, mass flow rate to the evaporator would still be maintained at the desired level.

Moreover, the present invention eliminates the need of a check valve, to prevent back-up of the liquid from the evaporator into the liquid supply mains as an evaporator is washed down with hot water when it has the suction line closed or when the evaporator is supplied with hot gas and the suction line of the evaporator is closed during a hot gas defrost period.

Thus, it will be observed how in operation the invention delivers to the inlets of various evaporator circuits a flow that is constant, and how the stated objects and novel results are attained.

What is claimed is:

1. A liquified refrigerant feed control comprising a housing having an inlet and an outlet for the flow of gas 1n its liquid phase therethrough, a first conduit interconnecting the inlet and the outlet having spaced flow control means disposed in series for limiting the volume of liquid flowing through said conduit, 2. first one of said flow control means limiting the flow of liquid to said outlet, a second one of said flow control means being movable in said conduit for varying the quantity of flow of liquid from said inlet to first one of said flow control means, a second conduit interconnecting said inlet and outlet, means reciprocably mounted in said second conduit for movement responsive to a pressure differential between said inlet and outlet, and means interconnecting said reciprocably mounted means and one of said flow control means for movement of the latter by the former to vary the amount of flow of liquid through the other flow control means to maintain a constant flow at the outlet at a predetermined pressure below the liquid pressure at the inlet.

2. The combination called for in claim 1 in which said spaced control means each comprise valve ports facing the outlet and valve elements cooperating therewith, and said reciprocably mounted means comprises a valve port facing the outlet, a piston reciprocably mounted in said second conduit responsive to said pressure differential, and a valve member carried by said piston closing against said valve port, an adjustable stop means for limiting the opening movement of the valve element of said other flow control means, said means interconnecting said piston and the valve element of said one of said flow control means for adjusting said valve element with respect to said pressure differential, and resilient means urging closure of said piston valve element and opening of said valve element of said one of said flow control means for establishing and controlling said pressure dilferential.

3. The combination called for in claim 1 in which said reciprocably mounted means is balanced against relative movement when pressures on opposite sides thereof are equalized, spring means urging said piston and thereby said one of said flow control means to its open position to maintain in association with said other flow control means a constant pressure differential across the piston and a constant flow through said conduits.

4. The combination called for in claim 1 in which said reciprocably mounted means and said one of said flow control means each include a backflow check valve.

5. The combination called for in claim 1 including an adjustable stop means controlling the opening of said one of said flow control means having a control shaft, means for substantially reducing heat conductivity of said control shaft, a finned sleeve carried by the housing and enclosing said shaft, indica means carried by said sleeve and shaft cooperating to indicate the flow potential of said one of said flow control means.

6. The combination called for in claim 1 in which said second conduit and said reciprocably mounted means comprise a cylinder and piston therein and includes a valve port bordered by a tapered valve seat, and a valve member having a valve head cooperating with said valve seat with a seat of greater taper for contact at a radial distance spaced from said cylinder, the effective pressure areas of said reciprocably mounted means and the flow control means exposed to pressure in said inlet being substantially equal and opposite, and resilient means urging said valve head to its closed position.

7. The combination called for in claim 1 in which said serially spaced flow control means each include a valve port and a valve member, the reciprocably moved valve member including a castellated sleeve element telescoping in the valve port in which the castellations having converging edges and the other valve member having a castellated sleeve element telescoping in its valve port in which the castellations have substantially parallel edges.

8. A liquified refrigerant feed control comprising a housing having an inlet and outlet, a first conduit interconnecting said inlet and outlet, a valve port facing the outlet mounted in said conduit, pressure responsive member having a valve element closing against said valve port, resilient means urging said pressure responsive element in the direction closing said valve, a second conduit interconnecting said inlet and outlet having spaced valve ports facing towards said outlet, a first valve member connected to said pressure responsive element and cooperating with one of said valve ports, said first valve member being urged by said resilient means to its wide open position and moved by said pressure responsive element to its closed position, a second valve member cooperating with the other of said valve ports opening in the direction of flow of liquid from said inlet to said outlet, means for limiting the opening of said second valve to throttle flow therethrough.

9. The combination called for in claim 8 including resilient means urging closure of said second valve member for operation thereof as a back flow check valve in association with said pressure responsive member to block reverse flow of liquid in said conduits.

10. In a refrigerating system having a refrigerant sup ply line, a suction line and means for supplying said supply line with liquid refrigerant under a pressure greater than its vapor pressure therein, an evaporator circuit discharging to the suction line comprising an evaporator, means in said evaporator circuit for reducing the pressure in said suction line and evaporator below the vapor pressure of the refrigerant, and an evaporator feed control means in said circuit between said evaporator and said supply line for supplying said circuit with liquid from said supply line at a constant rate of flow and a pressure appreciably above the pressure at the outlet of said evaporator, said feed control means including flow control means for establishing a predetermined rate of flow through said feed control means, a variable opening valve connected in series with said flow control means, and means responsive to the pressure differential across said flow control means and said variable opening valve for adjusting said variable opening valve to maintain a constant pressure drop across said feed control means at said flow rate.

11. The combination called for in claim 10 wherein said evaporator circuit includes a refrigerant pressure reducing means downstream of said feed control means re ducing the pressure of the refrigerant in the evaporator to a pressure less than its vapor pressure therein.

12. The combination called for in claim 10 wherein said evaporator circuit includes a refrigerant expansion means between said feed control means and said evaporator reducing the pressure of the refrigerant in the evaporator below the controlled pressure at the outlet of said feed control means.

13. The combination called for in claim 10 in which a surge drum interconnects said suction and supply lines and said supply line and includes a liquid re-circulating pump which feeds cold, low pressure liquid refrigerant to said feed control means at a pressure above its vapor pressure therein.

14. In a refrigerating system having a refrigerant supply line, a suction line and means for supplying said supply line with liquid refrigerant under a pressure greater than its vapor pressure therein, a evaporator circuit discharging to the suction line comprising an evaporator, means in said evaporator circuit for reducing the pressure in said evaporator to below its vapor pressure therein, and an evaporator feed control means in said circuit between said evaporator and said supply line for supplying said circuit with liquid from said supply line at a constant fiow and pressure appreciably above the pressure at the outlet of said evaporator and comprising a housing having an inlet connected to said supply line and an outlet connected to the evaporator circuit for the flow of refrigerant in its liquid phase therethrough, a first conduit interconnecting the inlet and the outlet having serially spaced flow control means for limiting the volume of liquid flowing through said conduit, the downstream one of said flow control means limiting the flow of liquid to said outlet, the upstream one of said flow control means being movable in said conduit for varying the quantity of flow of liquid from said inlet to said downstream flow control means, a second conduit interconnecting said inlet and outlet, means reciprocably mounted in said second conduit for movement responsive to pressure differential between the inlet of said downstream valve and said outlet, and means interconnecting said reciprocably mounted means and said upstream one of said flow control means for movement of the latter by the former to vary the amount of flow of liquid to said downstream flow control means to maintain a constant flow at the outlet at a determined pressure below the liquid pressure at the inlet.

15. In a refrigerating system having a refrigerant supply line, a suction line and means for supplying said supply line with liquid refrigerant under a pressure greater than its vapor pressure therein, an evaporator circuit discharging to the suction, line comprising an evaporator, means in said evaporator circuit for reducing the pressure in said evaporator to below its vapor pressure therein, and an evaporator feed control means in said circuit between said evaporator and said supply line for supplying said circuit with liquid from said supply line at a constant flow and pressure appreciably above the pressure at the outlet of said evaporator and comprising a housing having an inlet connected to said supply line and an outlet connected to the evaporator circuit for the flow of refrigerant in its liquid phase therethrough, a firstconduit interconnecting the inlet and the outlet having serially spaced flow control means for limiting the volume of liquid flowing through said conduit, the upstream one of said flow control means limiting the flow of liquid from said inlet to the downstream flow control means, the downstream one of said flow control means being movable in said conduit for varyingtthe quantity of flow of liquid to said outlet, a second conduit interconnecting said inlet and outlet, means reciprocably mounted in said second conduit for movement responsive to pressure differential between said inlet and the outlet of the upstream flow control means, and means interconnecting said reciprocably mounted means and said downstream one of said flow control means for movement of the latter by the former to vary the amount of flow of liquid to said outlet 12 to maintain a constant fiow at the outlet at a determined pressure below the liquid pressure at the inlet.

References Cited UNITED STATES PATENTS 2,374,568 4/1945 Terry 137-503 2,387,364 10/1945 Terry 137503 XR 2,617,265 11/1952 Rutt 62512 XR 3,020,892 2/1962 Arbogast 137-503 MEYER PERLIN, Primary Examiner.

US. Cl. X.R.

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