US3005319A

US3005319A - Refrigeration apparatus with hot gas defrost

Info

Publication number: US3005319A
Authority: US
Inventors: Leslie B M Buchanan
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1959-12-01
Filing date: 1959-12-01
Publication date: 1961-10-24
Anticipated expiration: 1978-10-24

Description

REFRIGERATION APPARATUS WITH HOT GAS DEFROST Filed D60- 1, 1959 FIG].

Oct. 24, 1961 L. B. M. BUCHANAN 2 Sheets-Sheet 1 EVA =ORATOR INVENTOR CONDEN SER FIGZ.

H H LESLIE B.M.BUCHANAN Mag/ ATTO R N EY al 8 5 2 h I.

REFRIGERATION APPARATUS WITH HOT GAS DEFROST Filed Dec. 1, 1959 Oct. 24, 1961 a. M. BUCHANAN 2 Sheets-Sheet 2 INVEN TOR LESLIE B. M. BUCHANAN ATTORNEY 3,005,319 REFRIGERATION APPARATUS WITH HOT GAS DEFROST Leslie B. M. Buchanan, Galloway, Ohio, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Dec. 1, 1959, Ser. No. 856,566

7 Claims. (Cl. 62-156) This invention relates to refrigeration apparatus and more particularly to an improved control system for socalled hot gas, or bypass, defrosting systems.

More particularly, this invention concerns an improved arrangement and control system for a valve which alter natively permits compressed refrigerant to flow through a restrictor into a refrigerant evaporator or to bypass the restrictor and flow directly into the evaporator for effecting, respectively, refrigeration or defrosting of the evaporator. In accordance with this invention, actuation of the defrost valve to initiate defrosting and subsequent actuation thereof to terminate defrosting is effected autnited States atent O matically in response to conditions of operation of the refrigerator employing the refrigeration system.

This invention constitutes an improvement upon the defrost valve arrangement and control described and claimed in my Patent No. 2,957,316, issued October 25, 1960, entitled Refrigerating Apparatus With Hot Gas Defrost Means, and assigned to the same assignee as this invention.

' The principal object of this invention is reliable and accurate control of defrosting for a refrigeration system, which objective is achieved through the use of a relatively simple, inexpensive valve and control mechanism capable of reliable performance. over an extended period of time.

In accordance with this invention a unitary selfactuating hot gas bypass valve is so disposed in the refrigerant circuit that there is a flow of warm refrigerant through the body of the valve during both refrigerating and defrosting operations. By this arrangement, heat from the warm refrigerant maintains the components of the valve at a sufiiciently elevated temperature to preclude condensation of moisture on the exposed surfaces thereof even though portion of the valve may be subjected to a cooling effect from low pressure, vaporizable refrigerant fiuid. Moreover, the valve is so connected into the refrigerant circuit that its automatic self-closing function is performed in response to pressure conditions existing at or near the outlet of the evaporator. This feature of the improved valve gives more reliable defrost termination; first, because the valve responds to the condition of that portion of the evaporator which is last to defrost and, second, the pressure responsive portion of the valve is not subjected to the initial inrush of high pressure refrigerant to the evaporator at the inception of the defrost operation, which cause premature termination of defrosting with some prior defrost controls. Also, sensing the pressure at the outlet end of the evaporator eliminates the eifect of pressure drop through the evaporator. This varies with different evaporators, and different compressor pumping rates.

Another novel feature of the improved defrost control of this invention resides in the mechanism provided for automatically actuating the bypass valve to open position to initiate defrosting in response to theoccurrence of a predetermined number of refrigerator operations. Specifically, the problem solved by this invention is the provision of a reliable mechanism for opening the defrost valve and immediately thereafter freeing the movable portion of the valve for automatic closing at the termination of the defrost operation.

The control of this invention also includes a temperature responsive compensating feature which assures reliable operation of the control under conditions of unusually low, and unusually high, ambient temperature.

Other objects, advantages and features of the invention will be made apparent by the following detailed description which refers to the accompanying drawings wherein:

FIG. 1 is a perspective view of a domestic refrigerator adapted to employ this invention;

FIG. 2 is an enlarged sectional view of the improved defrost control of this invention together with a schematic illustration of the refrigerating circuit with which it is used;

FIG. 3 is a sectional view of the defrost control taken generally as indicated by the line -IHIII in FIG. 2;

' FIG. 4 is a diagrammatic view of the defrost control illustrating a valve opening operation of the control; and

FIG. 5 is a fragmentary perspective view of the valve actuating mechanism of the control.

Referring to FIG. 2 in detail, the improved defrost control of this invention is identified generally by the reference numeral 11 and is particularly adapted for use in a compressor-condenser-evaporator refrigeration systern. The system illustrated includes a motor-compressor unit 12 for compressing vaporous refrigerant which is condensed in a condenser 13 and conveyed through a restrictor device 14 into a low pressure evaporator or cooling unit 15, wherein the refrigerant is vaporized to absorb heat. Vaporous refrigerant is returned to the inlet of the motor-compressor unit 1'2 through a suction conduit 16. Similar conduit means are employed to serially connect the motor-compressor unit 12, the condenser 13, the restrictor 14 and the evaporator 15. Refrigerating systems of this type are frequently employed to refrigerate food storage compartments of domestic refrigerators, such as that illustrated in FIG. 1. The evaporator 15 of the circuit may be disposed within a compartment 17 of the refrigerator for absorbing heat therefrom and the condenser 13 of the circuit disposed exteriorly of the compartment for dissipating heat to air ambient the refrigerator.

In a hot gas, or bypass, type defrostable refrigerating system, with which this invent-ion is concerned, there is provided a bypass line or conduit 18 for conveying compressed refrigerant directly to the evaporator 15, bypassing the restrictor 14. Warm vaporous refrigerant conveyed to the evaporator 15 by this line adds heat to the evaporator to effect removal of ice and frost which collects thereon. Control of the flow of refrigerant fluid through the bypass conduit 18 is exercised by a valve, indicated generally at 19, forming a part of the defrost control 11. This valve is disposed in the conduit means connecting the'discharge outlet of the motor-compressor unit 12 and the restrictor 14 and, preferably, upstream of the condenser 13 in the conduit carrying hot discharge gas from the motor-compressor 12.

The defrost control valve 19 includes a body 21 formed of metal or other good heat conducting material which contains refrigerant flow passages 22 and 22a that provide an inlet 23 and two outlets 24- and 25 for the valve. Disposed within the valve body 21 for movement in the flow passages 22 is a valve member 26 which cooperates with a seat 27 for establishing or disestablishing refrigerant flow through valve outlet 25 communicating with the bypass conduit 18. When the valve member 26 in in its closed position as shown in FIG. 2 (i.e., seated against seat 27), refrigerant entering the valve body 21 is prevented from flowing into the bypass conduit 18 and is constrained to flow through outlet 24 to the condenser 13 and subsequently to the restrictor 14. The valve member 25 is movable to an open position (illustrated in FIG. 4) in which it is displaced from its seat 27, whereby refrigerant is permitted to flow into the bypass conduit 18.

It is to be noted that regardless of the condition of the defrost control valve 19, warm refrigerant is conveyed through the passages of the valve body 21 whenever the motor-compressor 12 is operated. Heat imparted to the valve body 21 is conducted to other elements of the control valve to warm these elements and prevent condensation of moisture from the ambient air thereon. As is explained in greater detail below, this warming effect is particularly beneficial with regard to prolonging the life of the defrost termination means of the valve, which includes a pressure responsive device in the form of a bellows 28 which is brazed, or otherwise secured, in fluidtight relationship, to the valve body 21. Expansion of the bellows 28 in response to an increase in fluid pressure within the evaporator of the refrigerating system is employed to actuate valve member 26 to its closed position to terminate defrosting. For this purpose, the interior of the bellows 28 in is communication with a portion of the refrigerant circuit through a passage 29 in the valve body 21 and a pressure line 3-1 having one end secured to the valve body and opening into passage 29 and having its other end in communication with a portion of the suction conduit 16, preferably near the outlet of the evaporator, as indicated at 32 in FIG. 2.

Movement of an end wall portion 33 of bellows 28 is transmitted to the movable valve member 26 by means of a valve stem 34, which has a fluid-tight connection with the bellows wall 33 and is affixed to the valve member 26. The stem 34 slides in an elongated bore provided in a sleeve portion 36 of the valve body 21. As can be readily appreciated, a close fit is provided between stem 34 and the sleeve 36 to minimize leakage of refrigerant vapor from valve passage 22 into the interior of the pressure responsive bellows 28. It will be noted, however, that the interior of the bellows 28 is in communication with a portion of the refrigerant circuit which is operating at a lower pressure than the refrigerant flowing through valve passages 22 and that any refrigerant leaking into the bellows 23 will be carried away through pressure line 31.

It is to be expected that a small quantity of higher pressure refrigerant will leak by valve member 26 during refrigerating operation in spite of efforts to provide for tight seating of valve member 26 against its seat 27. Ex pansion of such refrigerant in valve passage 22a, of course, refrigerates the valve body 21 and by conduct-ion cools the bellows 28. Under some conditions, this might tend to promote condensation of water on the body of the valve and on the bellows. This could have a detrimental effect on the life of the control valve. This condition is obviated by the refrigerant flow arrangement of this invention because, as mentioned previously, during all operating periods of the system warm refrigerant is conveyed through the valve body 21. The latter, being constructed of good heat conducting material, conveys heat from the Warm refrigerant to the bellows and other portions of the valve to keep the temperature of these elements sufiiciently high to preclude the condensation of moisture thereon.

The valve member 26 is moved to its closed position to terminate defrosting when the bellows 28 senses the existence of a pressure condition at the outlet of the evaporator 15 which indicates that the temperature of the evaporator has risen to some value above 32 F., so that all frost and ice has been melted therefrom. The jointure of pressure line 31 connecting bellows 28 into the refrigerant circuit at point 32 near the outlet of the evaporator 15 is desirable for reliable defrost termination. The exit end of the evaporator, generally, is the last portion of the evaporator to defrost and the sensing of evaporator pressure for defrost termination purposes should, therefore, be done at this point. This connection location also minimizes the pressure surge to which the defrost termination bellows 28 is subjected at the beginning of a defrosting operation. It can readily be appreciated that the surge of high pressure refrigerant into evaporator 15 immediately following opening of defrost valve 19 will be damped, or dissipated, in the passages of the evaporator and premature closing of valve 19 as a result of this pressure surge will be avoided.

The pressure at which the bellows 28 effects closing of the valve member 26 is determined by restraining means forming a part of the control 11 and adapted to restrain movement of the valve stem 32 until the predetermined pressure occurs. This restraining means preferably takes the form illustrated in the drawings and includes a lever 37, which is pivotally mounted on a pin 38 and has an intermediate portion thereof bearing against an exposed end portion 39 of the valve stem 34. The end of the lever -37 opposite pin 38 carries a roller 40 which is adapted to be engaged and restrained by a detent spring member 41 when the lever 37 occu-. pies a raised position in which it elevates the valve stem 34 and lifts valve member 26 from its seat 27. This condition is illustrated in FIG. 4, from which it will be noted that the roller 40, and consequently the lever 37, are restrained against downward, or counterclockwise, movement by an offset finger 42 formed in the lower end portion of the detent spring 41. The holding force or effect of the detent spring 41 is overcome when suffia cient pressure exists within the bellows 28 to apply force through the valve stem 34 to the lever 37 to cause the roller 40 to push the detent spring 41 to the right and ride over the finger 42 on that spring.

The optimum defrost termination pressure may vary from one refrigeration system to another and it is, therefore, desirable to provide means for adjusting the restraining force ofiered by the detent spring 41. In the preferred embodiment illustrated, this adjustment is made possible by the manner of mounting the detent spring 41 within the control 11. As best shown in FIGS. 2 and 3, the spring 41 is pivotally carried on a fulcrum 43 formed in the control casing. The end of the spring opposite the finger 42 bears against an adjusting screw 44, also mounted in the control casing. For the arrangement illustrated in FIG. 2, turning adjusting screw 44 to move it downwardly increases the clockwise biasing force of the spring 41 to increase the pressure required in bellows 28 to cause the roller 40 to ride over the spring detent finger 42. Conversely, turning adjusting screw 44 to move it upwardly decreases the bias afforded by spring 41 and, consequently, decreases the value of the defrost termination pressure in bellows 28.

It is also recognized that the optimum defrost termination pressure may vary with changes in ambient temperature. Under high ambient temperature conditions, the quantity of heat which is available from the motorcompressor unit 12 to warm refrigerant being pumped to the evaporator 15 during defrosting is higher than under average temperature conditions, with the result that that portion of the evaporator through which refrigerant flows is rapidly elevated in temperature. Other, more remote, portions of the evaporator structure and other frost covered portions of the refrigerator may lag behind the refrigerant carrying portion and actually still have frost or ice remaining thereon when the pressure of the refrigerant in the refrigerant carrying portions of the evaporator rises to the value for which the defrost control valve 19 is set to close. To overcome this problem it is desirable to increase the period of defrost during high ambient temperature conditions to provide sufficient time for the most remote portions of the evaporator to defrost. This can be accomplished by raising the pressure value at which the defrost control is set to close.

A different condition exists under extremely low ambient temperature conditions, of the order of =60 F. and below. In low room temperatures an increasing quantity of refrigerant in the system is absorbed in the body of lubricating oil contained in the motor-compressor unit 12 and, in part, circulating through the refrigerating system. The resulting decrease in the quantity of refrigerant being circulated through the system limits the maximum pressure which may occur in the evaporator. Under extreme conditions, this maximum pressure may be less than that pressure which is required to close the defrost control valve under average operating conditions. It is, therefore, desirable to lower the pressure setting of the defrost control valve under extremely low ambient conditions to provide insurance against'the possibility of the pressure in the evaporator never reaching defrost termination pressure.

. In accordance with this invention, the defrost control includes means for respectively increasing or decreasing the restraining force acting in opposition to the valve closing forces from the bellows 28 in accordance with a rise or a fall in ambient temperature. In the first place, the defrost control 11 is preferably located in the vicinity of the motor-compressor unit so as to be subjected to substantially the same temperature conditions as the motor-compressor. In addition, the detent spring 41 of the restraining means is formed of a bimetallic strip to provide automatic variation of the force characteristics of the spring with changes in ambient temperature. In the embodiment. of the invention illustrated in FIGS. 2 and 3, the more active material of the bimetallic spring 41 is located on the back face of the spring 41 (Le, to the right as the spring is viewed in FIG. 2). Thus, an increase in ambient temperature prompts the spring 41 to deflect to the left (as viewed in FIG. 2) to increase the restraining force applied to the roller 40 by the spring finger 42; Conversely, a decrease in ambient temperature causes the spring 41 to tend to move to the right relieving in part the restraining force offered to the roller 40. Because the restraining force imposed on roller 40 is transmitted to the bellows 28 through the lever 37 and the valve stem 34, the bias of spring 42 directly determines the pressure required to be sensed by the bellows 28 in order to close valve 19 and effect termination of a defrosting operation.

Any suitable provision may be made for initiating a defrost operation by moving the valve control lever 37 from the position shown in FIG. 2 to the position shown in FIG. 4. For example, this may be accomplished manually by the user of the refrigerator. However, in accordance with this invention, it is preferable that initiation of the defrosting operation take place in response to certain conditions of operation of the refrigerator in which the system is employed. In the illustrated apparatus, means are provided for initiating defrosting when the refrigerator door has been opened and closed a predeterminednumber of times. As has been previously known, the accumulation of frost and ice on the evaporator of a domestic refrigerator is related to opening and closing of the refrigerator door.

Referring to FIG. 1, the refrigerator cabinet is provided with a plunger 46 which projects from the front of the cabinet and is en-gageable by a portion of the cabinet door 50 when the door is moved to closed position. This plunger 46 forms a part of the defrost control 11 and is an extension of a slider 47 (see FIGS. 2 and 3) mounted for reciprocating movement in the control casing. Each time the refrigerator door 50 is closed it engages plunger 46 and moves slider 47 to the left, as viewed in FIG. 2. Rightward movement of the slider 47 and extension of plunger 46 when the refrigerator door is opened is effected by a spring 48.

- Reciprocations of the slider 47 are reflected in rotary movement of a ratchet wheel 49 having a plurality of teeth 51 on the periphery thereof, presenting an annular series of drivensurfaces which are engageable by a spring pawl 52 carried by slider 47. The majority of the pawl teeth 51 have the same configuration and the driven surfaces they present to the pawl 52 are uniformly spaced about the periphery of the ratchet wheel, thus enabling the pawl 52 to effect equal increments of rotation of the wheel 49 for most of the reciprocating movements of the slider 47. One region of the ratchet wheel 49, however, is provided with an enlarged tooth 53 adapted to cause a large increment of rotation of the wheel 49 for one reciprocation of the slider 47, the purpose of which is explained hereinafter. This is accomplished because the driven surface of tooth 53 presented to the pawl 52 isv spaced a greater peripheral distance from the driven surface of the tooth 51 preceding it in the direction of wheel movement than the uniform distance between adjacent teeth 51.

Mounted on the ratchet wheel 49 for rotation therewith are a pair of cam surfaces 54 and 55 having follower surfaces engageable, respectively, with a valve actuating arm 56 and a return arm 57. The follower surface of cam 54 is substantially cylindrical except for a small arcuate portion thereof which contains a cutout 58 adapted to loosely receive a follower shoe 59 carried by actuating arm 56. Cam 54 is adapted to restrain movement of the valve actuating arm 56 against the bias of an actuating spring 61 connected to the arm 56 and to release the actuating arm at that point in its rotary movement at which the follower shoe 59 is aligned with cutout 58. It can be seen that when the shoe 59 is aligned with cutout 58 the actuating arm 56 is free to move clockwise about a pivot pin 60 so that a finger 62 projecting from the end of actuating arm 56 engages lever 37 and moves it to open the defrost control valve 19. Actuating arm 56 is released once in each revolution of cam 54 to initiate a defrosting operation. The number of door openings required to rotate cam 54 through a complete revolution is determined by the number of teeth on the ratchet wheel 49. It has been determined that satisfactory operation can be obtained by initiating defrosting each time the refrigerator door has been opened and closed twenty-nine times, so approximately twenty-nine teeth may be provided on ratchet wheel 49.

Return arm 57 of the valve operating mechanism is employed to return actuating arm 56 to the position shown in FIG. 2 to free valve lever 37 from the influence of the actuating arm 56 immediately after valve 19 has been opened. The'follower surface on cam 55, which controls movement of return arm 57, has a spiral configuration with its high point terminating in an abrupt cutoff 63. When cam 55 is rotated to the point at which the cutoff 63 is moved beyond the end of return arm 57 a return spring 64 connected to return arm 57 rotates the latter counterclockwise about the pivot pin 60 and a portion of arm 57 engages a finger 66 on actuating arm- 56 and moves arm'56 away from the valve lever 37. In order for this operation to take place it is necessary that return spring 64 apply a greater turning moment to return arm 57 than is applied to actuating arm 56 by actuating spring 61.

The angular position relationship between the cutout 58 of cam 54 and the cutofl? 63 of cam 55 is such that the release of actuating arm 56 is effected prior tothe release of return arm 57 but only a small increment of rotation of the ratchet wheel 49 separates release of the two

arms

56 and 57. The object of this arrangement is to enable the release of actuating arm 56 and its return, through release of the return arm 57, to be eifected in that increment of rotation of the ratchet wheel 49 which can be effected by a single reciprocation of the slider 47. Certain manufacturing tolerances must, of course, be permitted with respect to the relative locations of the cam cutout58 and the cam cutofi 63 as well as in the configuration of those portions of

arms

56 and 57 which are engaged by earns 54 and 55. A definite increment of rotation, say on the order of 5 degrees, should be provided in the camming system between the release of

arms

56 and 57 to prevent premature release of the return arm 57, which malfunction prevents opening the defrost valve 19 at the desired time. It is necessary, therefore, that ratchet wheel 49 be rotated a sufiicient amount to insure the release of the return arm 57 after the release of actuating arm 56. In accordance with this invention, the ratchet wheel 49 is caused to undergo a larger incre- 7 ment of rotation at that increment in its rotation in which the arms 56; and 57 are released. This increased increment of movement is effected by the enlarged tooth 53 on the ratchet wheel and which is disposed in a region of the ratchet wheel which is presented to the slider pawl 52 as the

arms

56 and 57 are to be released.

It should be apparent that the extent of movement and path of movement of the slider pawl 52 is such that it will normally pick up the next tooth on the ratchet wheel 49 whether it be one of the smaller teeth 51 or the large tooth 53.

In operation of the improved defrost control valve 19 and the control therefor, defrosting is initiated when the refrigerator door has been opened and closed a sufilcient number of times to bring cam cutout 58 in alignment with shoe 59 on actuating arm 56. Movement of actuating arm 56 under the action of spring 61 lifts valve actuating lever 37 sufficiently to cause the valve member 26 to be lifted from its seat, thereby admitting warm refrigerant directly to the evaporator through bypass conduit 18. The valve 19 is retained opened by the action of detent spring 41 on roller 40 carried by lever 37. Immediately following release of the actuating arm 56 and during the same movement of slider 47 caused by closing the refrigerator door, the return arm 57 is released to return actuating arm 56 to the position shown in FIG. 2 in order to permit the defrost control valve 19 to be automatically closed to terminate defrosting. The valve 19 is closed when bellows 28 senses the defrost termination pressure at the outlet of the evaporator 15 which is suflicient to overcome the restraining force of detent spring 41.

Subsequent reciprocations of slider 47, effected by opening and closing of the refrigerator door 50, rotate ratchet wheel 49 and

cams

54 and 55 counterclockwise as viewed in FIG. 2. The gradual rise on the spiral follower surface of cam 55 moves return arm 57 in small increments against the bias of its spring 64. This gradual movement of return arm 57 requires relatively light actuating forces on the plunger 46 and slider 47. When cam 55 has been rotated suificiently to commence clockwise rotation of return arm 57 away from finger 66 on the actuating arm '56, the cutout in cam 5-4 will have been rotated out of alignment with the actuating arm shoe 59, which then comes to rest against the cylindrical surface of cam 54. Movement of the actuating arm 56 in a direction to actuate defrost control valve 19 is thus prevented until cutout 58 is again aligned with shoe 59.

While the invention has been shown in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications without departing from the spirit thereof.

What is claimed is:

l. Refrigerating apparatus including a compressor, a condenser, a restrictor, an evaporator, said elements being connected in series flow circuit in the order named, said compressor having an inlet and an outlet, valve means connected to said circuit between the outlet of said compressor and said restrictor, a bypass conduit providing for refrigerant flow from said valve means to said evaporator bypassing said restrictor, said valve means having a body portion formed of good heat conducting material and having refrigerant flow passages therein, the refrigerant flow circuit between said compressor outlet and said restrictor extending through one of the passages in said valve body, a valve member movable to closed and open positions in said passages for directing refrigerant respectively to said restn'ctor or to said bypass conduit, means for moving said valve member to its open position, a device responsive to an increase in suction pressure beyond a predetermined value-for actuating said valve member to its closed position, said device being carried by said body portion in heat transfer relation therewith, and a pressure line connecting said device to said circuit between said evaporator and the inlet of said compressor subjecting said device to the pressure in said circuit between said evaporator and said compressor inlet in closing direction of said valve member.

2. Refrigerating apparatus including a compressor, a condenser, a restrictor, an evaporator, conduit means connecting said elements in series flow circuit in the order named, said compressor having an inlet and an outlet, valve means connected to said conduit means between the outlet of said compressor and said restrictor, a bypass conduit providing for refrigerant flow from said valve means to said evaporator bypassing said restrictor, said valve means having a body portion formed of heat conducting material and having refrigerant flow passages therein, the refrigerant flow circuit between said compressor outlet and said restrictor extending through one of the passages in said valve body, a valve member movable to closed and open positions in said passages for directing refrigerant respectively to said restrictor or to said bypass conduit, means for moving said valve member to its open position, a bellows responsive to an increase in suction pressure beyond a predetermined value carried by said body portion in heat transfer relation therewith for actuating said valve member to its closed position, and a pressure sensing line connecting said bellows to said conduit means between said evaporator and the inlet of said compressor, said bellows being subjected to atmospheric pressure in a direction opposite to the closing direction of said valve member and being subjected to the pressure in said conduit means between said evaporator and said compressor inlet in the closing direction of said valve member.

3. Refrigerating apparatus including a compressor, a condenser, a restrictor, an evaporator, conduit means connecting said elements in series flow circiut in the order named, said compressor having an inlet and an outlet, valve means in said circuit between the outlet of said compressor and said restrictor, a bypass conduit providing for refrigerant flow from said valve means to said evaporator and bypassing said restrictor, said valve means having a body portion having refrigerant flow pasages therein, a valve member movable to closed and open positions in said passages for directing refrigerant respectively to said restrictor or to said bypass conduit, a device responsive to an increase in suction pressure beyond a predetermined value for actuating said valve member to its closed position, a presure line connecting said circuit from between said evaporator and the inlet of said compressor to said device whereby said device is subjected in closing direction of said valve member to the pressure in said circuit between said evaporator and said compressor inlet, means for moving said valve member to its open position, and means for applying a restraining force to said valve member when said member is in its open position, the force applied by said last named means being varied in relation to changes in arm bient temperature.

4. A valve structure including a valve movable to closed and open position, means for moving said valve from open position to closed position, and means for ac. tuating said valve to open position comprising an actuating arm biased for movement from a first positlon to a second position, a return arm for returning said actuating arm to its first position, cam means having first and second follower surfaces for, respectively, restraining movement of said actuating armaway from its first position and con trolling movement of said return arm, said surfaces said cam means being shaped to effect release in rapid succession of said actuating arm and then said return arm whereby said actuating arm moves from 1ts first po sition to its second position for actuation of said valve and is immediately returned to its first position to permit self-actuation of the valve, a toothed ratchet for driving said cam means and a reciprocating pawl for effecting incremental movement of said ratchet, said ratchet lii b tantially uniform tooth configuration except 9 in the region thereof engaged by said pawl as said cam means is moved to efiect release of said arms, said region of the ratchet having an oversize tooth thereon for effecting increased movement of said cam means to insure release of both of said arms.

5. A se" actuating valve structure for defrostable refrigerator systems comprising a valve body having refrigerant fiow passages therein, a valve member movable to closed and open positions for controlling flow of refrigerant through said passages, means for moving said member from its closed position to its open position, a pressure sensitive device for moving said member from its open position to its closed position, and a spring detent applying a force to said valve member restraining movement thereof in closing direction, said detent comprising a bimetallic member which increases its restraining force in response to increase in ambient temperature.

6. A valve structure comprising a valve body having fluid flow passages therein, a valve member movable to closed and open positions for controlling flow of fiuid through said passage, means for actuating said valve member to open position comprising an actuating arm biased for movement from a first position to a second or valve open position, a return arm for returning said actuating arm to its first position, cam means, means for driving said cam means, said cam means having first and second follower surfaces for, respectively, restraining movement of said actuating arm from its first position and controlling movement of said return am, said surfaces of said earn means being shaped to effect release in rapid succesion of first said actuating arm and then said return arm whereby said actuating arm moves from its first position to its second position for actuation of said valve member to open position and is thereafter returned by said return arm to its first position to permit closing of the valve member, and means independent of said actuating means for moving said valve member from open position to closed position; said valve member when moved to open position by said actuating member remaining in open position until closed by said last named means.

7. A valve structure including a valve member movable to closed and open positions, means for actuating said valve to open position including an actuating arm biased for movement from a first position to a second or valve opening position and a return arm for returning said actuating arm to its first position, cam means having first and second follower surfaces for, respectively, restraining movement of said actuating arm away from its first position and controlling movement of said return arm, said surfaces of said cam means being shaped to effect release in rapid succession of first said actuating arm and then said return arm during one incremental movement of said cam means following a plurality of preliminary incremental movements of said cam means whereby said actuating arm moves from its first position to its second position for opening of said valve and is immediately thereafter returned to its first position by said return arm, and means for driving said cam means for effecting one incremental movement at a time of said cam means repeatedly through said preliminary movements and then said one movement, said driving means including a movable element and a reciprocable pawl for effecting incremental movement of said movable element, said movable element comprising a series of first members which are spaced apart to present uniformly spaced drive surfaces to said pawl, and a second member on said element presenting to said pawl a drive surface which is spaced fro-m the drive surface of the first member preceding it, in the direction of movement of said movable element, a distance greater than the space between the drive surfaces of said first members; the incremental movement of said movable element effected by engagement of said pawl with said second member cor-responding to said one incremental movement of said cam means, whereby said cam means is moved a greater incremental distance during said one incremental movement than during said preliminary incremental movements.

References (Iited in the file of this patent UNITED STATES PATENTS 2,344,215 Soling Mar. 14, 1944 2,666,298 Jones a Jan. 19, 1954 2,717,494 Doeg Sept. 13, 1955 2,743,587 Hubacker r May 1, 1956