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Publication numberUS2195220 A
Publication typeGrant
Publication dateMar 26, 1940
Filing dateFeb 7, 1938
Priority dateFeb 7, 1938
Publication numberUS 2195220 A, US 2195220A, US-A-2195220, US2195220 A, US2195220A
InventorsWilliam L Mcgrath
Original AssigneeHoneywell Regulator Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Refrigeration system
US 2195220 A
Abstract  available in
Images(2)
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Claims  available in
Description  (OCR text may contain errors)

M ,1940. v w. L. McGRATH 2,195,220

REFRIGERATION SYSTEM Filed Feb. 7, 1938 2 Sheets-Sheet 1 Juventor March 26, 1940. w. MOGRATH 2,195,220

' REFRIGERATION SYSTEM 2 Filed Feb. '7, 1938 2 Sheets-Sheet 2v Fig. 8'

Jnvmtor William L. Mc Grath attorney tion to provide an electrical operating means for a refrigeration expansion valve, and a self contained superheat responsive unit mounted within the evaporator outlet for controlling the electrical operating means.

A further object of my invention is the provision of an indicating means for indicating the degree of superheat of the refrigerant within said outlet, said means being operated by the same unit that controls the electrical operating means for the valve.

Other objects will become apparent upon a study of the specification, claims, and appended drawings, wherein like reference characters represent like parts in the various views, and in which Figure 1 is a diagrammatic view of a refriger ation system illustrating one form of valve controlling means embodying my invention;

Figure 2 is a similar view illustrating a second form of valve controlling means, and

Figure 3 is a similar view illustrating a third form of valve controlling means.

Referring more specifically to Figure 1, the conventional compression type refrigeration system is illustrated. This system includes a compressor ill for withdrawing refrigerant from evaporator ll through a pipe l2, the refrigerant being compressed and then flowing through a pipe iii to a condenser It. The condensed refrigerant flows from the condenser I4 through pipe iii to a receiver l6 whence it flows through pipe I! to an expansion valve II, and from this expansion valve the expanded refrigerant flows into the evaporator Ii through pipe it.

The compressor i0 may be controlled in any well known manner and for purposes of illustration I have shown a high pressure cut-out 20 and a suction pressure controller 2i. High pressure cut-out 20 may include a bellows 22 connected by means of a pipe 22 to the outlet of the compressor ii. A lever 24 pivoted at 25 is urged against the top of the bellows 22 by tension spring 26, lever 24 carrying a mercury switch 21. The suction pressure controller 2| may include a bellows 30 connected by means of a pipe II to the suction side of the compressor ll. Bellows 30 operates a lever 22 pivoted at 31, this lever being held against the upper portion of bellows 38 by means of a tension spring 34. A mercury switch 35 is carried by the lever 32. When the switches are in the positions illustrated, current flows through the compressor motor and the refrigeration system is in operation, the current flowing through the motor by means of the following circuit: from line wire 40, through conductor ll, mercury switch 21, conductor 42, mercury switch 35, conductor 43, through the compressor motorand through conductor 44 to a line wire 45. Line wires 4. and 45 may be connected to a suitable source of power (not shown). The compressor II will stop whenever the pressure on the high pressure side reaches an excessive value or when the pressure on the suction side drops to a low enough value, as will be apparent from the drawings.

Expansion valve 18 controls the flow of refrigerant from the receiver It to the evaporator II and a motor is provided for operating the valve it. A gear Si is driven by the motor 50 and engages a rack 52 connected to valve stem 53 of the valve i8, and rotation of the motor in one direction or the other causes the opening or closing of the valve member l8. Power is conveyed to the motor 50 by means of line wires 55 and 58. Motor ill may be a floating motor of any suitable type and may comprise a pair of field windings, energization of one causing rotation of the motor in one direction and energization of the other causing rotation of the motor in the other direction. Terminals 51, 58, and 59 are provided on the motor and may be so connected to the field windings that when terminals 51 and 58 are connected together the motor 50 rotates in a direction to cause the valve to move towards closed position, and when terminals 58 and 59 are connected together the motor rotates in a direction to move the valve towards open position.

For controlling the direction of the rotation of the motor 50, a controller generally designated by the reference character 60 is provided, this controller being responsive to the degree of superheat at the outlet of the evaporator. This controller includes an operating bellows i l mounted within the evaporator outlet and containing a volatile fill which may be the same as the refrigerant being used in the system. A plate 62 is connected to the bottom of the bellows SI and a vertically extending rod 63 is connected to the plate 62. For preventing escape of refrigerant from the system about the rod H, a sealing bellows 64 may be provided, this bellows being of smaller size than bellows 8 I. The operating bellows 6i and sealing bellows I may be connected to a plate 55 mounted in the enlargement 66 of the connection between the evaporator ii and compressor III. A cap member I! may be provided for enclosing the sealing bellows ll. Rod N is connected at 10 to a lever ll pivoted at 12. A spring member I! biases the lever H in a clockwise direction. The opposite end of the lever II is formed of a suitable conducting material 15 insulated from the rest of the lever H by insulating material ll. Portion II of lever H is connected by means of a conductor 11 to the terminal 8 of the motor ll. Contacts I9 and III which are connected to the terminals 51 and 59 of the motor, respectively, by means of conductors ll and 82 are arranged to be engaged by the portion ll of the lever ll upon the existence of certain conditions in the evaporator outlet, as will be hereinafter explained. Engagement of member II with contact ll causes terminals 51 and ll of the motor II to be electrically connected, whereupon the motor rotates in a direction to close the valve ll. Similarly, when member 15 engages contact ll, terminals I8 and II of the motor are connected together and the motor rotates in a direction to open the valve II.

when the pressure at the outlet of the evaporator increases, an upward force is exerted on the bottom of the bellows ll, whereupon lever ll tends to rotate in a clockwise direction. An increase in temperature at the outlet of the evaporator tends to expand the refrigerant sealed within the bellows II and thus a downward pressure is exerted on the bellows since bellows ii is of larger size than bellows I, and the lever H tends to rotate in the opposite direction. It will therefore be apparent that movement of lever II depends both upon the pressure of the refrigerant in the evaporator outlet and also upon the temperature of the refrigerant in the evaporator outlet. As the refrigerant becomes superheated, the force exerted downwardly on the bellows 6| becomes greater than the force degree of superheat becomes high enough the lever II will move far enough so that the end II of the lever engages contact 80, whereupon motor 50 is energized and rotates in a direction to cause valve I8 to open thus allowing the e of more refrigerant into the evaporator. As the amount of refrigerant passing into the evaporator increases, a large portion thereof becomes available for cooling purposes and the refrigerant leaving the evaporator becomes less superheated, whereupon the lever "tends to move in a clockwise direction and to break the circuit between terminals 58 and 590! the motor 50, whereupon the motor and valve come to rest. If the amount of refrigerant flowing through the evaporator is too high so that complete evaporation thereof does not take place within the evaporator, the refrigerant leaving the evaporator will be in a saturated state and as no superheat is available to move lever II in a counter-clockwise direction, the lever will rotate in the opposite direction until end I thereof engages contact I9, whereupon the motor rotates in a direction to cause the valve to move towards closed position. In this manner, the position of the 'valve I8 is controlled in accordance, with the superheat at the outlet of ,the evaporator and the major portion of the evaporator will be available for cooling purposes at all times.

In order to be able to ascertain what the degree of superheat of the refrigerant leaving the evaporator is at any time, an indicating scale is provided at the left end of the lever II, this lever being pointed as illustrated and the scale being suitably graduated. The upper portion of the scale may represent a saturated condition of the refrigerant and the lower portion of the scale may indicate a condition of high superheat 'of the refrigerant. In this manner, lever "II is utilized for controlling the operation of the motor 50 and also for indicating to the attendant at any time what the degree of superheat of the refrigerant leaving the evaporator is.

Referring now to Figure 2, a refrigeration system identical with that of Figure 1 is illustrated. In this figure, however, a diflerent kind of motor for operating the valve I8 may be employed, this motor being represented by the reference character 90. This motor may be of the type illustrated in Patent No. 2,028,110 to D. G. Taylor issued on January 14, 1936, and may include a pair of opposed relay coils connected together at one .end, the junction of these coils being connected to terminal 9| of the motor. The opposite ends of the coils may be connected to terminals 92 and 98, respectively. Motor 90 may also include a pair of field windings, one of these windings being energized when one of the relay coils becomes more highly energized than the other and causing the motor to rotate in one direction, and when the other relay coil becomes more highly energized the other field winding is energized and causes rotation of the motor in the opposite direction. The motor also includes a balancing potentiometer which causes the relay coils to be rebalanced after suflicient rotation of the motor.

Connected to the junction of the relay coils by means of a center tap resistance 98 and a conductor 94 is the portion I5 of lever II, this lever being operated in the same manner as described in connection with Figure 1. The end .15 of the lever is arranged to move over a potentiometer resistance 95 as'the degree of superheat of the refrigerant varies, this potentiometer coil being connected by means or conductors I1 and. to

terminals 92 and 93, respectively, and accordingly to the ends of the relay coils. Lines 55 and 56 are also connected to the ends of the relay coils and hence it will be seen that when portion 15 of lever II is in the mid position of the potentiometer coil 95, the relay coils within the motor will be equally energized. Upon upward movement of portion .I5of arm 'II over resistance 95, the coil connected between terminals 9| and 92 of the motor becomes the more highly energized coil and the motor is caused to rotate in a direction to cause'the valve to move towards open position. After the motor has rotated an amount suflicient to cause the arm of the balancing pctentiometer to move a distance sufficient to counteract the efiect of the movement of the arm I5, the relay coils will again be equally energized, neither winding of the motor will be energized and the motor'will come to rest. It is accordingly seen that the motor 90 will operate an amount proportional to the movement of arm I5 over resistance 95, or in other words, an amount proportional to the change in superheat of refrigerant in the evaporator outlet, whereby the degree of superheat may be maintained sub-' stantially uniform.

Mounted in the space being cooled is a bulb I00 containing a 'volatile' fluid andbeing connected by means of a capillary tube IM to a bulb I00 containing a volatile fill. An arm I03 pivoted at I04 is held against the top of bellows I02 by a spring I05. As the temperature within the space being cooled increases, the fluid within the bulb I00 expands and causes expansion of the bellows I02 and movement of the arm I03 upwardly. Conversely, as the temperature falls the arm I03 will move downwardly by reason of the contraction of the volatile fluid in the be]- lows I02. The arm I03 includes an end portion I08 electrically-insulated at I09 from the rest of the arm I03, and the portion I08 is arranged ing connected in parallel by means of conductors III and II2to the potentiometer resistance 95.

The portion I08 of the arm I03 is connected by means of a conductor II5, resistance H6, and conductor III to the conductor connecting terminal 9| of motor 90 and the member I5 of potentiometer 95. It will, therefore, be apparent that member I08 and resistance IIO form a potentiometer connected in parallel with the potentiometer 95. The provision of resistance H3 in the circuit connecting terminal 9| of the motor and arm I08 desensitizes this potentimeter. In other words, a greater movement of arm I08 over resistance [I0 is required to give the same efiect to the motor than a movement of arm 15 over resistance 95, so that the main con-, troller for the'motor is the superheat responsive device and the potentiometer H0 operated by the space temperature responsive device produces a compensating efiecton the motor. As the space temperature rises, the degree of super- -heat at the outlet of the evaporator should be reduced so that a greater portion of the evaporator coilisavailable for cooling purposes. This increase in temperature is accomplished by movein the motor 90. 'I'hisalso shifts'the'control 7 range of potentiometer" 95 downwardly, and the center tap resistance 96 insures that the width of the control range does not vary even though the position of the control range is shifted by potentiometer 'IIO.

It will, accordingly, be seen that in this figure the valve I8 is controlled in the first place by the superheat in the outlet of the evaporator and is also controlled by the temperature in the space being cooled so that as the cooling requirements for the space increase the degree of superheat in the outlet of the evaporator will decrease thus making available for cooling purposes a greater portion of the surface of the evaporator.

In Figure 3 a refrigeration system similar to those of Figures 1 and 2 is illustrated. The expansion valve in this figure is shown in cross section, this valve including an inlet I20, an outlet I2I, a valve seat I22, and a valve element I23 cooperating with the seat I22 for controlling the flow of refrigerant through the valve. The upper end of valve I23 is formed as an armature I24 which is located within a solenoid I25 and the position of the valve element I23 is controlled by the energization and deenergization of the solenoid I25. This solenoid may be wound on a cylindrical member I26 connected to the valve body by means of a nut I2'I. Mounted on top of the cylindrical member I26 by means of bolts I28 is a plate I29 and screw threaded within this plate is a bolt I30 which is enclosed by a sealing bellows I3I, this sealing bellows being sealed at its upper end to the cylindrical member I26 in any suitable manner as by soldering it thereto. The lower portion of bolt I30 forms a limit for the upward movement of the valve element I23 thus limiting the amount of opening of the valve and by turning the bolt I30, the amount of openingof the valve may be varied as will be apparent. A cap member I32 may be screw-threaded to the plate I29 to enclose the top of the bolt I30.

A controller I35 responsive to superheat of the refrigerant leaving the evaporator is provided for controlling the energization of solenoid I25.

' This controller may include a power bellows I36 similar to the power bellows H of Figures 1 and 2 and sealed at the bottom to a plate I31, this bellows being mounted within the evaporator outlet and enclosing a volatile fill which may be the same as the refrigerant used in the system. Extending upwardly from plate I3'I is a rod I36 connected at its upper end to a spring retaining assembly I40. A sealing bellows I is provided for sealing the upper end of this rod to a plate I42 to which the upper end of the power bellows I36 may be suitably connected. A housing I45 is screwed into the upper end of the enlargement I46 of the evaporator outlet and holds the plate I42 firmly in place, suitable packing I41 being provided to prevent leakage of refrigerant from the evaporator outlet. In the upper end of housing I45 is mounted a screw-threaded member I46 connected to a nut I49 supported by the exterior of the housing I45. The lower end of member I48 is connected to a spring retainer I50 and a tension spring I5I connected to the spring retainers I40 and I50 serves to urge the spring retainers towards one another. The downward movement of member I50 is limited by th' nut I49 so that the spring I5I serves to contract the power bellows I 36 and move the rod I36 upwardly.

Mounted on the plate I42 and suitably insulated therefrom by means of insulation I52 is a contact member I53. A second contact member suitably connected to the spring retainer assembly I40 and insulated therefrom is designated by the reference character I54. Contact I53 is connected by means of conductor I to the solenoid I25 and contact I54 is connected by means of conductor I6I to the line wire 40. The other end of solenoid I25 is connected by means of conductor I62 to the line wire 45. It will, therefore, be apparent that engagement of contacts I53 and I54 will close a circuit from the line wire 40 through the solenoid I25 and back to the line wire 45, thus energizing the solenoid and causing movement of valve member I23 to open position. Movement of the bellows I36 is effected in the same way as in Figure 1. Thus an increase in pressure in the evaporator outlet causes the bellows to contract whereas an increase in temperature at the evaporator outlet causes the volatile fill withinthe bellows I36 to expand and thus cause the bellows to move downwardly, this latter movement of the bellows being opposed by the spring I5I. Thus when the degree of superheat at the evaporator outlet reaches a high enough value so that bellows I36 expands causing rod I36 to be moved downwardly thus moving contact I54 into engagement with contact I53, the solenoid I25 becomes energized thus opening the expansion valve and allowing more refrigerant to pass to the evaporator. After the degree of superheat has dropped to a low enough value, bellows I36 will be contracted due to the combined effects of the pressure within the evaporator outlet and the spring I5 I, thus moving contact I54 away from contact I53, deenergizing solenoid I25 and causing the valve I23 to again close. Thus in this form of the invention, the valve is at all times either in open or closed position so that instead of a modulating control, a two-position control is effected. The amount of superheat required to cause the valve to be opened may be varied by adjusting the nut I49 upon the threaded member I46. A cap I10 may be screwthreaded to the top of the housing I45 and enclose the adjusting nut I49.

The spring retainer assembly I40 may have connected thereto an arm III arranged to move across the graduated scale I12 whereby the degree of superheat of the refrigerant at all times at the outlet of the evaporator may be noted by an attendant.

If desired, a thermostat could be wired in series with the solenoid, so that when the temperature of the space being cooled dropped below a predetermined value, the valve would be closed, thus preventing the flow of refrigerant to the evaporator.

It will, accordingly, be seen that in the various forms of my invention an expansion valve has been provided which is operated by an electric motor or a solenoid, the motor or solenoid being controlled in turn by the superheat of the refrigerant at the outlet of the evaporator. In this manner, large expansion valves as may be used in large refrigeration systems may be controlled by the superheat at the evaporator outlet without requiring a large amount of superheat to effect the opening of the valve as may be the case where the valve is operated directly by a superheat responsive device. Accordingly, since less superheat is required to cause the opening of the valve, the superheat at the outlet of the evaporator may be maintained at a lower degree and a larger portion of the evaporator surface may be available for cooling purposes.

Having described three forms of my invention.

other modifications may become apparent to 14 those skilled in the art, and I wish it to be understood that my invention is limited only by the scope of the appended claims.

I claim as my invention:

l. A refrigeration system including a condenser and an evaporator, a valve for controlling the flow of refrigerant from the condenser to the evaporator, means for controlling the position of said valve, movable means located adjacent the evaporator outlet positioned in accordance with the amount of superheat at the outlet of the evaporator for controlling said position controlling means in accordance with the position of said movable means, and means responsive to the condition of the air being cooled also in control of said position controlling means.

2. A refrigeration system including a condenser and an evaporator, a valve for controlling the flow of refrigerant from the condenser to the evaporator, electrical means for controlling the position of said valve, and means directly responsive to the amount of superheat at the outlet of the evaporator for controlling said electrical means.

3. In a refrigeration system including a condenser and an evaporator, a 'valve for controlling the ilow of refrigerant from the condenser to the evaporator, an electric motor for causing movement of said valve to closed position upon rotation thereof in one direction and for causing movement of said valve to open position upon rotation of said motor in the other direction, means directly responsive to a condition of high superheat of refrigerant for causing rotation of said motor in valve opening direction, and means directly responsive to a condition of low superheat for causing movement of said motor in valve closing direction.

4. In a refrigeration system including a condenser and an evaporator, a valve for controlling the flow of refrigerant from the condenser to the evaporator, a bellows containing a volatile fluid positioned within the outlet of the evaporator and sealed therefrom, motor controlling means operated thereby in response to variations in pressure differential inside and outside of said bellows occasioned by variations in superheat of the refrigerant leaving the evaporator. and motor means controlled by said motor con trolling means for operating said valve.

5. In a refrigeration system including a con- .denser and an evaporator, a valve for controlling 6. In a refrigeration system including a condenser and an evaporator, a valve for controlling the flow of refrigerant from the condenser to the evaporator, a solenoid for causing the opening of said valve in response to the energization thereof, a bellows containing a volatile fluid, said bellows being positioned at the evaporator outlet so as to be subjected to variations in the superheat of the refrigerant at said outlet, and circuit controlling means for said solenoid operated by said bellows, whereby said solenoid is energized when the superheat at the evaporator outlet reaches a predetermined value.

7. In a refrigeration system including a condenser and an evaporator, a valve for controlling the flow of refrigerant from the condenser to the evaporator, a controller for said valve including an expansible chamber containing an expansible fluid, said chamber being remotely located from said valve, and being subjected to the refrigerant leaving the evaporator so as to expand and contract in accordance with the degree of superheat existing at the evaporator outlet, and means operated by said chamber to cause said valve to assume positions corresponding to the degree of superheat of the refrigerant at the evaporator outlet.

8. In a refrigeration system including a condenser and an evaporator, a valve for controlling the flow of refrigerant from the condenser to the evaporator, a controller for said valve including an expansible bellows located within the evaporator outlet and being sealed therefrom, said bellows containing a volatile fluid whereby said bellows expands and contracts in accordance with the degree of superheat existing at the evaporator outlet, said valve being operatively connected to said bellows whereby the amount of opening of said valve varies in accordance with the degree of superheat of the refrigerant at the evaporator outlet, and means operated by said bellows for indicating the degree of superheat of the refrigerant at said outlet.

9. In a refrigeration system including a condenser and an evaporator, a valve for controlling the flow of refrigerant from the condenser to the evaporator, a control device responsive to the degree of superheat of the refrigerant at the evaporator outlet, an indicator for indicating the degree of superheat of the refrigerant at the evaporator outlet, and means connecting said control device, and said valve and indicator whereby the valve is controlled in accordance with the degree of superheat and the degree of superheat is indicated by said indicator.

10. In a device of the class described, an enclosure for a fluid, an expansible chamber located within said enclosure and sealed therefrom, said chamber containing a volatile fluid, said chamber being subjected on the exterior thereof to the pressure of the fluid within said enclosure and on the interior thereof to a pressure corresponding to the temperature of the fluid within said enclosure whereby said chamber expands or contracts in accordance with the superheat of the fluid within said enclosure, and means operated by said chamber for indicating the de-' gree of superheat of the fluid in said chamber.

11. In a refrigeration system including a condenser and an evaporator, a valve for controlling the flow of refrigerant from the condenser to the evaporator, an impervious bellows containing refrigerant located within the evaporator outlet and sealed therefrom, said bellows depending from the upper wall of said outlet, a rod extending upwardly through said bellows and connected to the lower portion thereof whereby changes in superheat of refrigerant surrounding said bellows causes vertical movements of said rod, and means responsive to movements of said rod for causing operation of said valve.

12. In a refrigeration system including a condenser and an evaporator, a valve for controlling the flow, of refrigerant from the condenser to the evaporator, an impervious bellows containing refrigerant located within the evaporator outlet and sealed therefrom, said bellows depending from the upper wall of said outlet, a rod extending upwardly through said bellows and connected to the lower portion thereof whereby changes in superheat of refrigerant surrounding said bellows causes vertical movements of said rod, and indicating means operated by said rod for indicating the amount of superheat of refrigerant at the evaporator outlet.

13. in a refrigeration system including a condenser and an evaporator, a valve for controlling the flow of refrigerant from the condenser to the evaporator, an impervious bellows containing refrigerant located within the evaporator outlet and sealed therefrom, said bellows depending from the upper wall of said outlet, 9. rod extending upwardly through said bellows and connected to the lower portion thereof whereby changes in, superheat of refrigerant surrounding said hellows causes vertical movements or said rod,-

means responsive to movements of said rod for causing operation of said valve, and indicating means operated by said rod for indicating the amount of super-heat of refrigerant at the evaporator outlet.

i l. A refrigeration system including a condenser and an evaporator, a valve for controlling the flow of refrigerant from the condenser to the evaporator, means for controlling the position of said valve, movable means located adjacent the evaporator outlet positioned in accordance with the amount of superheat at the outlet of the evaporator for controlling said position controlling means in accordance with the position of said movable means, and means for varying the position of said valve for a given position of said movable means.

15. In a refrigeration system including a condenser and an evaporator, a valve for controlling the flow of refrigerant from the condenser to the evaporator, a controller for said valve including an expansible chamber containing an expansible fluid, said chamber being located adjacent the evaporator outlet and being subjected to the reirigerant leaving the evaporator so as to expand and contract in accordance with the degree of superheat existing at the evaporator outlet, power transmitting means between a movable wail of said chamber and said valve whereby the valve assumes positions corresponding to the degree of superheat of the refrigerant at the evaporator outlet, and means for adjusting the position of said vaive for a given position of said movable wall.

WILLIAM L. McGRATH.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2467219 *Dec 21, 1942Apr 12, 1949Willard L MorrisonMultistage refrigerating apparatus
US2504435 *Nov 24, 1942Apr 18, 1950Gen Controls CoSystem for controlling refrigeration
US3271971 *Dec 31, 1964Sep 13, 1966Westinghouse Electric CorpLow pressure cut-outs for refrigerant compressors
US3498075 *Jan 22, 1969Mar 3, 1970William A ZumbielRefrigeration control apparatus
US3808827 *Mar 7, 1973May 7, 1974Avon ERefrigeration unit
US5477701 *May 3, 1995Dec 26, 1995Parker-Hannifin CorporationApparatus and method for mass flow control of a working fluid
US5522231 *Jul 26, 1995Jun 4, 1996Parker-Hannifin CorporationApparatus and method for mass flow control of a working fluid
US6460354Mar 2, 2001Oct 8, 2002Parker-Hannifin CorporationMethod and apparatus for detecting low refrigerant charge
WO1994017346A1 *Jan 18, 1994Aug 4, 1994Parker-Hannifin CorporationSystem for controlling flow of working fluids
Classifications
U.S. Classification62/211, 337/320, 137/468, 338/41, 62/228.3, 337/332, 137/80, 337/331, 62/225, 251/26, 236/92.00B, 251/29, 92/40, 137/500, 200/81.4, 251/129.18, 137/553, 62/226, 251/14
International ClassificationF25B41/06
Cooperative ClassificationF25B2341/065, Y02B30/72, F25B41/062, F25B2600/21
European ClassificationF25B41/06B