US2115431A - Automatic defrosting and deicing system - Google Patents

Description

C DEFROSTING ND DE ICING S'Y'Sl'EM AUTOMA'JI INJENTOR John 02 aShivmy 5v i hnu d d ATTORNEY Patented Apr. 26, 1938 UNITED STATES PATENT OFFICE John J. Shively, New York, N. Y.

Application February 1, 1937, Serial No. 123,319

11 Claims.

This invention relates to improvements in automatic defrosting and de-icing systems.

An object of the invention is to provide a defrosting or de-icing system adapted to be controlled in response to the insulating value of an accumulation of frost, ice or the like.

Another object is to provide a control device comprising a normally insulated element and a normally uninsulated element, the latter adapted to acquire insulation during the operation of the apparatus to be controlled, the device being operable by joint influence of the two elements. Another object is to provide a device of the above character suitable for automatically controlling the defrosting or de-icing of refrigerating devices, the control being affected by the relative insulating values of the fixed insulation and of the frost or ice accumulated on the normally uninsulated element. A further object is to provide an automatic defrosting or de-icing device of the above character applicable to a refrigeration system of the intermittent type and including means operable by the above two elements to control the normal cycle of the system.

Other objects and advantages of the invention will become evident .during the course of the following description in connection with the attached drawings, in which Figure 1 is a longitudinal view of a preferred form of the device partly in section;

Figure 2 is a detail plan view of the switch contact members;

Figure 3 is a detail view of the trip lever and related parts;

Figure 4 is a detail view of the means for adjusting the trip mechanism;

Figure 5 is a cross sectional view of the normally insulated bulb applied to a cooling unit; Figure 6 is a similar view of the normally uninsulated bulb;

Figure 7 is a cross sectional view of an alternative form of the invention;

Figure 8 is a detail view of the mercury switch shown in Figure '7; s

Figure 9 is a similar view showing the mercur switch reversed;

Figure 10 is a similar detail view showing a mercury switch adapted for use in the device, Figure 7, but arranged to control two circuits;

Figure 11 is a diagram illustrating one embodiment of the device shown in Figure '7 in a refrigerating system; I

Figure 12 is a similar diagram illustrating the application of the device as shown in Figure 1 to a refrigerating system;

Figure 13 is a diagram illustrating the device as shown in Figure 7 arranged to control a piping system; 5

Figure 14 is a fragmental detail view of the toggle lever fulcrum arrangement; and

Figure 15 is a diagram illustrating an alternative application of the device to a flooded refrigerating system or the like. 10

Referring to Figure 1, the numeral I9 generally denotes a control device having a casing 20 preferably of non-conducting material such as bakelite. A rear plate 2| is secured in the casing 20. Two similar bellows members 22 and 23 have rear 15 mounting spuds 24 and 25 extending through the plate 2| and secured thereto by means of exterior nuts 26.

A tube 21, connected into the interior of the bellows 22 leads to a thermostatic bulb 28 adapt- 20 ed to be secured to a cooling unit represented herein by a refrigerating pipe 29. The bulb 28 may be secured directly in contact with the pipe 29 or may be thermally connected therewith through a saddle 30 of heat conducting material partly embracing both the pipe and bulb to facilitate conduction of heat between them. A jacket 3| of heat insulating material is disposed about the bulb 28 to insulate the greater part thereof from the surrounding air, a clamp 32 serving to 30 secure the above parts to the pipe 29.

A second tube 33, connected into the interior of bellows 23 through the spud 25, terminates in a second thermostatic bulb 34. -The bulb 34 is also secured to the cooling unit of which pipe 23 5 represents a part. The bulbs 28 and 34 may be secured to the same reach of pipe if desired, as illustrated diagrammatically in Figure 13.

The securing means for the bulb 34, herein illustrated by the metallic clamp 35, Figures 1 40 and 6, is adapted to transmit heat between the bulb and pipe 29, and no heat insulating jacket is provided around bulb 34.

From the foregoing it is evident that bulb 28 is thermally connected to the cooling unit but 45 thermally insulated from the surrounding atmosphere, while bulb 34 is also thermally connected to the cooling unit but is thermally exposed to the atmosphere. The bulbs 28 and 34 and their respective bellows and tube members 50 are charged in the usual manner with volatile fluids, preferably of substantially identical properties.

Bellows members 22 and 23 have forward heads 36 and 31 carrying central conical noses 38 and with an exterior knob 61.

39 engaging upper and lower arms 40 and 4| of a rocker 42, the arms 40 and 4| being depressed at the points of contact to maintain proper location of the noses 38 and 39. A V-shaped depression 43 in the middle of the rocker 42 engages a knife edge 44 on a lever 45 pivoted on a stationary pin 46. The lever 45 carries a spud 41 engaging the conical point 48 of a rod 49 having a central flange 50.

A compression spring 5| is disposed between a collar 52 loosely mounted on the rod 49 against the flange 50 and a second collar 53 threaded on the rod 49 adjacent the conical point 48. A second compression spring 54, similar in strength to spring 5|, is disposed between the front wall 55 of casing 20 and a third collar 56 threaded on the rod 49, the direction of threads. in collar 56 being opposite to that of collar 53. Collars 53 and 56 have forked extensions 51 and 58 engaging stationary pins 59 and 60 secured in the casing 20.

The forward end 6| of rod 49 has therein a cross pin 62 engaging longitudinal slots 63 and 64 in a hollow cylindrical member 65 rotatably retained in a plate 66 on the wall 55 and provided It will be seen that when the knob 61 is revolved the member 65 revolves the rod 49 through the cross pin 62. The stationary pins '59 and 60 prevent the collars 53 and 56 from turning, thus causing these collars to be moved along the revolving rod 49 in opposite directions due to their right and left-hand threads. Thus a rotation of the knob 61 causes one spring to be further compressed while the other is released an equal amount.

A second lever 68, also pivoted on the pin 46, Figure 1, carries on its free end a curved spring 69 to which is secured a contact bar 10 adapted to engage stationary electrodes 1| and 12 fastened to a block 13 in the casing 20. A fork 14' straddles the lever 45 and is pivoted to the free end thereof at 15. A tension spring 16 is stretched between a pin 11 in the free end of fork 14 and an eye 18 in an extension 19 of the lever 68. It will be understood that as the fork 14 and the lever 68 are shown in central section only one spring 16 is illustrated, but that a similar spring may be provided on the other leg of the fork.

A finger secured to lever 68 hastherein a notch 8| engaging the edge of the fork 14 as shown in Figures 1 and 14.

The action of the switch is as follows: In the position shown the pin 11 on the fork 14 lies to the left of the line of centers of stationary pin 46 and the eye 18 in the main switch lever 68. The tension spring 16 therefore exerts a pull toward the left on the lever 68, holding the contact bar 10 in contact with electrodes 1| and 12. When the lever 45 is moved to the left, as occurs when the spring 54 overcomes the pressures of bellows members 22 and 23 as hereinafter explained, the leftward motion of the pin 15 in the end of lever 45 also carries the pivoted end of the fork 14 to the left. As the fork 14 is restrained by the notched finger 80 from moving bodily, the fork swings clockwise in the notch. This motion continues until the pin 11 in the end of fork 14 passes the line of centers between stationary pin 46 and the eye 18. As the pin 11 passes to the right of this dead center position the spring 16 exerts a pressure to the right on the lever 68 which is thereby suddenly swung clockwise with a toggle action, withdrawing the contact bar 10 from the electrodes 1| and 12. The lever 68 starts its motion to the right the notched finger 80 also swings the fork 14 to the right past its dead center, since its fulcrum pin 16 has been moving to the left. The fork 14 thus is also snapped to the right and through the finger 80 exerts a leverage on the main switch lever which increases the energy of the latters opening motion. A stationary stop 82 is provided to limit the opening swing of the switch lever.

When the force of the bellows members increases the lever 45 is forced to the right, the entire foregoing action taking place as described except in reverse direction, causing the switch parts to he suddenly snapped into closed position as shown in Figure 1.

The rocker 42 has formed thereon or secured thereto a central arm 83 extending at right angles to the main portion. A foot 84 on the end of the arm 83 engages one arm 85 of a trip lever 86 which is pivoted to a block 81 on the rear plate 2| by means of a screw 88 as shown in Figures 1 and 3. A light tension spring 89 urges the arm 85 of the trip lever 86 into contact with the foot 84.

A channel-shaped lever 90, Figures 1 and 4, is pivoted to the casing 20 at 9|, and has an aperture 92 providing clearance around the flange 50, the sides 93 of the aperture 92 being curved to provide rocking or rolling engagement with the back of the collar 52. A pin 94 in the free end of lever has slidably mounted thereon a latch 96. A spring 96, Figure 4, urges the latch 95 along the pin 94, movement being restrained by a roller 91 on a bell crank 98 pivotally secured to the casing 20 by a pin 99. Movement of the bell crank 98 is in turn restrained by an adjusting screw I00 threaded through the front of the casing 20 and provided with an exterior head IOI, Figure 1. It will be seen that by screwing the screw I 00 inward or outward the position of the latch 95 on the pin 94 may be adjusted.

The free end of the latch 95 is provided with a hook 1102, Figures 1 and 3, adapted to engage the edge of the plate 2|. A light tension spring I03, diagonally disposed as shown in Figure 1, serves both to urge the latch 95 downward and to hold the sides 93 of the aperture 92 in the channel lever 90' against the collar 50. trip lever 86 normally engages the latch 95, as shown in Figures land 3, so as to guide the hook |02 free of the plate 2|. A depression I05, Figure 1, in the lower side of the latch 95 is provided for a purpose hereinafter explained.

A supply cord I06, led in through the plate 2|, has two conductors I01 and I01a. Conductor I01 is connected directly to the electrode 1|, while conductor I01a leads to a turn-off switch I08 of any suitable type from which a short lead I09 is connected to the electrode 12. The turn-off switch I08 is thus connected in series with the main switch, and is provided with an exterior manual control knob or button I I 0.

The operation of the device is as follows: Referring to Figure 12, the control device, generally denoted by the numeral I9, is connected in series with a motor III adapted to drive a refrigerating compressor IIZ. A discharge pipe 3 connects the compressor to a condenser I I4, from which a liquid line I I5 runs to the low side or cooling unit 29, the insulated bulb 28 and uninsulated bulb 84 being disposed in heat transmitting relation with the cooling element 29 as previously set forth. From the cooling unit the usual suction line H6 leads back to the compressor I I2.

Assuming the cooler 29 to be initially free from frost and the compressor in operation, the main switch lever 68 holding the contact bar 10 in en- The end I04 of gagement with the electrodes II and 12 as shown in Figures 1 and 2 and the manually operable switch I08 being closed, as the refrigerating system functions in the usual manner the temperature of the cooling unit falls. As both bulbs are thermally connected to the cooler 28, their temperatures also fall, and the consequent lowering of the pressures of their contained volatile fluids permits the bellows members 22 and 23 to contract under the urge of the compression spring 54, Figure 1.

when the temperature falls to a point pre-determined by the strength of the spring 54 the joint yielding of the two bellows members becomes sufllcient to allow the main switch arm 88 to be thrown to the right by the toggle action previously described, withdrawing the bar 10 from the electrodes II and 12 to break the circuit and stop the motor III. The cooling unit rises in temperature, the bulbs 28 and 34 also rising in temperature until joint expansion of the bellows members 22 and 23 again closes the toggle switch as previously set forth, to restore the system to operation. The device continues in the manner described to control the normal running cycle of the machine until defrosting action occurs, which comes about in the following manner:

Throughout the normal cycle described the temperatures of both bulbs rise and fall simultaneously in response to the temperature changes of the cooling unit. However, the bulb 34, being also thermally exposed to the warmer surrounding atmosphere, absorbs heat therefrom, while the bulb 28 due to the insulating jacket 3| is protected from such heat. As a result the temperature of bulb 28 follows closely that of the cooling unit 29 alone, but bulb 34, while also responding to the temperature changes of the cooling unit, is maintained at a higher temperature than bulb 28 throughout the entire operating range due to its absorption of atmospheric heat. Thus throughout the normal operating range the fluid pressure in bulb 34 is higher than that of 28. At all points in the range therefore, expansion of the bellows 23 remains greater than that of bellows 22, maintaining the rocker 42 inclined as shown in Figure 1.

In this position, as previously noted, the end I04 of trip lever 88 maintains the hook I02 clear of the plate 2|. As a result the latch 95 and lever 90 move to the right and left during the movements of the rod 49 and cap 52, the only opposition to the latters movement to the right being that the light retracting spring I03.

As frost begins to form on the cooling unit 29 it also forms around the outside of the uninsulated bulb 34 as indicated by the numeral II8, Figure 6. This formation around the bulb 34 interposes an insulating blanket between the bulb and the atmosphere, causing the bulb temperature to be influenced more closely by that of the cooling unit with a consequent nearer approach of the bulb temperature to the cooling unit temperature. As the frost blanket II5 around bulb 34 continues to increase in thickness its insulating effect also increases, so that the temperature and consequent pressure conditions of bulb 34 approach those of the insulated bulb 28.

As the pressure in bellows 23 approaches that in bellows 22 the formers length also approaches that of bellows 22, decreasing the angularity of the position of the rocker 42 and thereby causing the foot 84 to move the trip lever 86 clockwise, Figure 3. When the equalizing effect of the accumulated frost blanket has progressed sufllciently, the end I04 of trip lever 88 is carried clear of the latch 95. Thereafter, when the hook I! has been carried to the left of the plate 2| as shown in dotted and dashed lines in Figure 1, during the operating phase of the cycle, and thereafter starts its movement to the right during the idle phase, the hook engages the plate 2| which restrains its further movement. The lever 90 is thereby stopped and in turn stops the collar 52 from movement to the right. Thereafter, for the bellows members to move the rod 49 sufficiently to the right to re-close the toggle switch, their joint pressure must become sufficient to overcome not only the normal control spring 54 but also the auxiliary spring The additional pressure required for the bellows members to close the switch allows the cooling unit to rise to a defrosting temperature determined by the joint strength of springs 54 and 5|.

Since, due to the right and left hand threaded mounting of the collars 53 and 55, the total normal strength of the springs remains substantially equal during adjustment of the normal cycle control spring 54 by means of the knob 81, it is evident that the defrosting temperature remains substantially the same irrespective of adjustment of the cycling temperatures.

Defrosting having been completed and the joint pressure of the bellows members 22 and 23 having overcome both springs 5| and 54, the switch is reclosed as previously noted, restoring the system to operation. As the cooling unit temperature falls, the cooling of bulbs 28 and 34 causes the bellows members to relax their pressure and be once more contracted. However, as the bulb 34 is no longer insulated, it again absorbs atmospheric heat which causes its temperature drop to lag behind that of the insulated bulb 28. Consequently, the bellows 23 again retains a greater pressure and length than those of bellows 22, again tipping the rocker 42 as shown in Figure 1 and allowing the foot 84 to release the arm 85 of trip lever 80. When the depression I05 registers with the end I04 of the trip lever the spring 89 snaps the end I04 into the depression, the trip lever thereafter holding the latch 95 upward and preventing engagement of the hook I 02 until a new accumulation of frost again trips the device as described.

By moving the screw I00 inward or outward, as previously noted, the lateral position of the latch 95 may be adjusted as shown in Figure 4. This lateral adjustment changes the amount the end I04 of trip lever 86 must move in order to clear the latch and start the defrosting action. A change in the necessary movement of lever 86 entails a change in movement of the foot 84, which latter change can be effected only by a change in the nearness to equalization of pressures in the two thermostatic bulbs, in turn requiring a change in the amount of frost accumu lation. It is evident, therefore, that the amount of frost blanket necessary to initiate defrosting may be controlled by adjustment of the screw I00.

It should be noted that the defrosting action is controlled not by the mechanical thickness of frost accumulation but by its insulating effect as compared to that of a fixed insulation. It is immaterial whether the cooling unit be covered with dense icy accumulation or with very light dry frost, as the defrosting control will operate whenever the insulating effect of the accumulated blanket reaches the pie-determined value.

It further follows that the device is operable in substantially the manner described to control the accumulation of ice on cooling units submerged in water, as for instance in soda fountain water coolers, in which case the deposit II3, Figure 1, represents ice instead of frost. In other words, the operation is not confined to cooling units immersed in the atmosphere, as the device is operative in any fluid medium, either gaseous or liquid, which tends to deposit an insulating blanket during operation of the system's apparatus.

It will also be noted that while the control of the normal cycle is dependent on the average temperature and consequent pressure of the two bulbs, the defrosting operation of the device is dependent on changes of difference in pressures of the two bulbs rather than on their absolute pressures, so that this action is substantially independent of the absolute temperatures or temperature ranges of the operating system.

Figure 7 shows a simplified form of the device adapted for use in connection with systems having other means of controlling the normal operation, In this form the control unit, generally denoted by the numeral II1, has bellows members H3 and H3 corresponding to 22 and 23, Figure 1, secured to lugs I23 in a casing I2I. Tubes I22 and I23 connected into the bellows members H3 and H3 lead respectively as shown diagrammatically in Figure 13 to an insulated bulb I24 and an uninsulated bulb I25 adapted to be disposed on a cooling unit such as a pipe I23. The rocker I21, Figure '7, engaging the tapered noses I23 and I23 in the manner previously described, has a central V-notch I33 engaging a knife edge I on a lever I32 pivoted to the casing I2I at I33, the lever I32 being provided to maintain the rocker and bellows members in proper alinement.

A stud I34, secured in the wall of casing I2I, has screwed thereon a stepped collar I33. A compreasion spring I33 is disposed between the collar I33 and a cap I31, the latter having a central point I33 engaging a depression I33 in the lever I32 above the knife edge I3I.

The rocker I21 has formed thereon or attached thereto a central arm I43 extending downward between the bellows members.

In operation, the higher pressure in the bellows H3, due to its connection to the uninsulated bulb I23, Figure 13, normally maintains bellows III at greater expansion than bellows H3 in the manner previously set forth, thus keeping the arm I43 normally swung toward the right as shown in Figure 7. When the accumulation of frost on the normally uninsulated bulb causes equalization of the bellows pressures the arm I43 is swung to the left, and by its motion is adapted to actuate any suitable type of switch, in the present case illustrated by a mercury switch havirig a bulb I4I secured in a clip I42 on a shaft I43 rockably mounted in a support I44. The support I44 may be slidably mounted in the casing I2I and its lateral position may be adjusted by means of a screw I43 threaded into the support and rotatably retained in the casing I2I.

A lever I43 secured to the shaft I43 is adapted to laterally engage the end of the arm I43, while a lateral lever I 43a formed integrally with lever I43 extends through a slot I41 in the arm I43. The mercury switch illustrated in Figure 7 is arranged as shown in detail in Figure 8, that is with electrodes I43 and I43 in the right end of the bulb I and adapted to be electrically joined by a quantity of mercury I53 when the bulb is tipped to the right. a

When the arm I43, Figure 7, is swung to the left by equalization of the bellows pressures as noted above, it also swings the lever to the left, tipping the bulb I4,I to the right to close a circuit through the flexible leads I3I and I32 attached to the electrodes I43 and I43. with this arrangement it is evident that the tripping of the switch by the insulating action of accumulated frost closes the circuit. If desired, however, the position of the bulb I H in the clip I42 may be reversed so that the mercury contact is normally closed as shown in Figure 9, in which case the tripping of the device opens the circuit.

As defrosting progresses and both bellows members H3 and H3 expand against the pressure of the spring I33, the bottom of slot I41 in arm I43 encounters the lever I43a, raising the latter until, when defrosting is complete, the mercury bulb is again tipped to the left into normal position as shown, either breaking or restoring the circuit dependent on whether the bulb is arranged as shown in Figure 8 or Figure 9 respectively.

The device thus can be arranged either to complete a circuit when defrosting is required and to break the circuit when defrosting is completed or to break the circuit to cause defrosting and restore it upon completion thereof. A typical illustration of the first arrangement is shown diagrammatically in Figure 13, in which the device I I1 is adapted to control the opening of a solenoid valve I33 in a pipe line I34 carrying warm brine, not ammonia or other defrosting fluids such as are commonly directed through the cooling coils in certain types of refrigerating plants when defrosting is required.

The second arrangement, in which the circuit is broken to cause defrosting, is illustrated in Figure 11, wherein the device I I1 is electrically connected in series with the system's normal control thermostat I33. In this case the device normally remains closed while the thermostat I33 controls the usual operating cycle of the system, but when accumulated frost on the bulb I23 trips the device the circuit is opened until defrosting is completed.

The device arranged to break the circuit to cause defrosting may also be used as shown in Figure 13 when the pipe I34 is used as gas supply line for an absorption refrigeration system.

The point at which defrosting is completed and the switch thrown back to normal position may be adjusted by screwing the collar I33 up or down on the stud I34 to vary the pressure of the spring I33 applied to the bellows members H3 and H3. Also, by turning the screw I43 and thereby moving the support I44 and its supported parts laterally with respect to the arm I43, the tripping point and hence the required frost insulation to initiate defrosting may be adjusted.

From the foregoing description it is obvious that the device is adapted to operate in conjunctions with a wide variety of auxiliary devices such as solenoid valves, relays and the like. In some cases it may be desirable to control two circuits, in which event a mercury switch having two sets of electrodes arranged in opposite ends of the bulb I33 as illustrated in Figure 10 may be used.

In the case of certain flooded refrigerating systems or the like, wherein the low side fluid pressure of the refrigerant itself varies substantially in accordance with the temperature of the cooling coil, the insulated bulb 23 may be dispensed with and the tube 21 connected directly into the suction line 3 or other convenient means of access to the low side as in Figure 15. In this case the operation is substantially as described previously, the temperature and pressure in bulb ll approaching those of the cooling coil as frost or ice accumulates.

While the invention has been described in preferred form it is not limited to the precise structures illustrated, as various modifications may be made without departing from the scope of the appended claims.

What is claimed is:

1. In combination with a refrigerating system including a cooling unit and means to operate the same, a temperature responsive element thermally connected to said cooling unit and thermally exposed to a fluid medium surrounding said cooling unit, a second temperature responsive element thermally connected to said cooling unit and thermally insulated from said surrounding medium, and means connected to said elements and controllable by the difference in temperatures of said elements to disable said operating means and controllable by the average temperature of said elements to cause said operating means to function.

2. In combination with a refrigerating system including a cooling unit and electrical means to operate the same, a bulb disposed in heat exchange relationship with said cooling unit and thermally exposed to a fluid medium. engaging said cooling unit, an expansible bellows connected to said bulb, said bulb and bellows containing a thermostatic fluid, a second bulb disposed in heat exchange relationship with said cooling unit and thermally insulated from said medium, a second expansible bellows connected to said second bulb, said second bulb and said second bellows containing a thermostatic fluid, a switch adapted to control said electrical means, and means engaging both said bellows and operable by the joint expansion thereof to actuate said switch in one direction and responsive to the difference in expansion of said bellows to actuate said switch in the other direction.

3. In a device for use in a refrigerating system having a cooling unit and means to operate the safn e, said unit being immersed in a fluid medium adapted to deposit an insulating accumulation thereon, in combination, means connected to said cooling unit and containing a fluid variable in pressure substantially in sole correspondence to the change of temperature of said cooling unit, said means including a member expansible by said pressure, a second expansible member, a receptacle secured in heat exchange relationship with said cooling unit and, normally in heat exchange relationship with said fluid medium, a tube connectihg said receptacle to said second expansible member, a fluid in said receptacle, tube and second expansible member and variable in pressure in correspondence with changes of temperature in said receptacle, said receptacle being adapted to receive said accumulation and thereby become thermally insulated from said medium whereby the temperature in said receptacle may approach the temperature of said cooling unit to cause the expansion of said expansive members to approach equalization, and means engaging both said expansive members and operable by said approach to equalization to disable said first operating means and operable thereafter by joint expansion of said members to cause said first operating means to function.

4. A device as claimed in claim 3 including manual means to adjust the degree of said approach to equalization necessary to operate said disabling means.

5. In combination, a cooling unit, a thermostatic element in heat exchange relation with said unit and thermally insulated from a medium enveloping said unit and element, a second thermostatic element in heat exchange relation with said unit and thermally exposed to said medium, and switching means connected to both said elements and controllable jointly by said elements,

6. In a device of the character described, in combination, switching means, a pair oi. bellows members associated with said switching means and jointly expansible to actuate said switching means in one direction, resilient means opposing said bellows members and adapted to actuate said switch in the other direction, an uninsulated bulb connected to one of said bellows members and adapted to engage a cooling unit in heat exchange relation and to be thermally exposed to a medium enveloping said unit, a second bulb connected to said other bellows member and adapted to engage said cooling unit in heat exchange relation, said second bulb having a jacket adapted to thermally insulate the same from said medium, thermostatic fluids in said bulbs adapted to provide expansive pressures in said bellows members in accordance with the respective temperatures in said bulbs, means to augment the pressure of said resilient means, said augmenting means being normally disabled, and means responsive to the difference in respective expansions of said two bellows members to cause said augmenting means to function.

7. A device as claimed in claim 6 including means to adjust the pressures of said resilient means and means cooperative with said adjusting means to adjust the pressure of said augmenting means whereby the combined maximum operative pressures of said resilient means and said augnenitdng means may remain substantially cons an 8. In a device of the character described, in combination, thermostatic means including an element adapted to engage a cooling unit in heat exchange relationship therewith and to be thermally exposed to a medium enveloping said unit, a. second thermostatic means including a second element adapted to engage said cooling unit in heat exchange relationship therewith and having means to thermally insulate said element from said medium, a switch operable jointly by said two thermostatic means in accordance with the average temperatures in said elements within a pre-determined range, and means operable by said two thermostatic means in accordance with the difference in respective temperatures in said elements to modify said range.

9. In a refrigerating system, a refrigerating means, a medium to 'be refrigerated by said means, a member in thermal contact with said means and insulated from said medium, a second member in thermal contact with said means and in heat exchange relation with said medium, and a control device for causing said means to cease refrigerating, said device being conjointly controlled by both said members.

10. In a device of the character described, in combination, a rocker, an expansible bellows member engaging one end of said rocker, a second bellows member engaging the other end of said rocker, means to provide varying and mutually differing pressures in said two bellows members, a guide member rockably engaging the middle of said rocker, spring means urging said guide member against said rocker and said rocker against said bellows members in opposition to the exexpansion of said bellows members, an arm on tile fluid, a pressure responsive member connected to said unit and responsive to the pressure therein, a receptacle engaging said unit in heat exchange relation therewith and thermally exposed to an exterior fluid medium engaging said unit, said receptacle containing a thermostatic fluid, a second pressure responsive member connected to said receptacle and responsive to the pressure therein, and switching means associated with said first and second pressure responsive members and 10 operable jointly by said members.

JOHN J. SHIVELY.

Patent No. 2,115,431 Granted April 26, 1938 JOHN J. SHIVELY The above entitled patent was extended October 23, 1951, under the provisions of the act of June 30, 1950, for 5 years and 38 days from the expiration of the original term thereof.

Commissioner of Patents.

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