US2264545A

US2264545A - Refrigeration control system

Info

Publication number: US2264545A
Application number: US315503A
Authority: US
Inventors: Alwin B Newton
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1940-01-25
Filing date: 1940-01-25
Publication date: 1941-12-02
Anticipated expiration: 1958-12-02

Description

Dec. 2, 1941. NEWTON 2,264,545

REFRIGERAT ION CONTROL SYSTEM Filed Jan. 25, l940 QSnuenfo: l2 Alvin L B. Newtcm Home;

Patented Dec. 2, 1941 2,264,545 REFRIGERATION CONTROL SYSTEM Alwin B. Newton, Minneapolis, Minn, assignor to- Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application January 25, 1940, Serial No. 315,503

22 Claims.

This invention relates to a control system for a refrigerating apparatus and more particularly to a control system embodying means for automatically defrosting the evaporator of the refrigerating apparatus.

In the past, control systems have been applied to a refrigerating apparatus having an evaporator, a compressor, a condenser and a thermostatic expansion valve for stopping operation of the compressor at intervals to allow the evaporator temperature to increase above freezing for the purpose of defrosting the evaporator. However, in such systems the defrosting cycle is very often prolonged by reason of the fact that liquid refrigerant flow through the expansion valveinto the evaporator and expands therein during the defrosting cycle. In addition, certain of these automatic defrosting control systems utilize the evaporator pressure as a measure of defrosting tion to overcome the above mentioned diflicul ties. In carrying out this object of the invention, I propose to so arrange and construct the expansion valve of the refrigerating apparatus to prevent the supply of liquid refrigerant to the evaporator during the defrosting cycle. More specifically it is an object of this invention to so arrange and construct the expansion valve of the refrigerating apparatus to prevent the expansion valve from opening when the evap-v orator pressure rises above a predetermined value. Preferably this value corresponds to a temperature value below freezing so that at any pressure above freezing the valve will be closed whereby defrosting of the evaporator is assured. By rea son of this arrangement, the evaporator pressure can never rise above the predetermined value while the compressor is operating regardless of the cooling load because the valve will close when the pressure reache said value and this provides an additional advantage, namely, the load on the compressor motor is limited.

Other objects and advantages will become apparent to those skilled in the art upon reference to the accompanying specification, claims and drawing in whichv is diagrammatically illustrated the preferred form of this invention.

Referring now to the drawing, a compartment to be cooled is designated at I 0, this compartment being cooled by means of a cooling coil in the form of an evaporator I I. Refrigerant is circulated through'the evaporator I I by means of a refrigerating apparatus generally designated at l2 and for purposes of illustration it is assumed that the refrigerant used is dichlorodifluoromethane, commonly known as Freon 12. The refrigerating apparatus may comprise a compressor l3 operated by an electric motor I4. Compressed refrigerant is discharged from the compressor I3 through a high pressure line IE to a condenser IS. The condensed refrigerant is collected in a receiver I1 and flows through a liquid line I8 to the evaporator II. An expansion valve generally designated at I9 is located in the liquid line I8 for regulating the fiow of refrigerant to the evaporator II. Evaporated refrigerant is withdrawn from the evaporator I I through a suction line 20 by the compressor I3.

The compressormotor I4 and hence the compressor I3 is preferably controlled by an automatic defrosting control system and for purposes of illustration in this application this automatic defrosting control system is shown to comprise a temperature responsive controller 22 responsive to the temperature of the medium in the compartment I0 and a unitary control arrangement 23 responsive to changes in suction pressure and head pressure.

The temperature responsive controller may comprise a bellows 25 charged with a volatile fluid for operating a lever 26 against the action of an adjustable tension spring 21. The lever 26 operates a mercury switch 28 and for purposes of illustration it is assumed that when the temperature within the compartment I0 rises to 42, the mercury switch 28 is closed and when the temperature decreases to 40, the mercury switch 28 is opened.

The unitary control arrangement 23 may be of the type shown and described in application Serial No. 196,447, filed March 17, 1938, by Albert L. Judson and Carl G. Kronmiller. For purposes of illustration in this application, the unitary control arrangement is shown to comprise a bellows 30 connected by a pipe 3| to the suction line 20 so that the bellows 30 is operated-inaccordance with changes in suction or evaporator pressure. The bellows 30 operates a lever 32 the pressure setting of this portion of the unitary control arrangement may be varied at will. The lever 32 carries an insulating pad 33 which in turn carries contacts 31 and 33 which are electrically connected together. The contact 31 is adapted to engage a contact member 33 carried by a terminal 40 and the contact 33 is adapted to engage a contact member 4| carried by a terminal 42. are urged into engagement with concentrically mounted and independently rotated cams 43 and 44. By independently rotating the cams 43 and 44 the contact members 39 and 4| may be independently adjusted with respect to the contacts 31 and 38. For purposes of illustration, it is assumed that as the suction pressure increases the contact 31 first engages the contact member 39 at pounds and then the contact 33 engages the contact member 4| at 35 pounds. Upon a decrease in suction pressure the contact 33 first disengages the contact member 4| at 35 pounds and then the contact 31 disengages the contact member 33 at 15 pounds. Since the refrigerant utilized in the system is dichlorodifluoromethane a suction pressure of 35 pounds represents an evaporator temperature of substantially 38. Therefore the contact 31 is moved into engagement with the contact 39 only when the evaporator temperature has risen to 38 following defrosting ofthe evaporator.

The unitary control arrangement 33 may also comprise a bellows 45 connected by a pipe 43 to the high pressure line I! so that the bellows 45 is operated in accordance with changes in head pressure. The bellows 45 operates a lever The contact members 33 and 4| 41 fulcrumed on a fulcrum member 43 against the action of an adjustable tension spring 43.

One end of the tension spring 43 is connected to the lever 41 and the other end :is-connected to an adjusting screw arrangement 83 which is lever 41 adjustably carries an abutment member 5| made of insulating material and having

abutment surfaces

52 and 53. The abutment surface 52 is adapted to engage a contact member 54 carried by a terminal 55 for moving the ,contact member 54 out of engagement with a contact 56. The abutment surface 53 is adapted to engage a contact member 51 carried by the terminal 42 for moving the contact member 51 out of engagement with a contact 53. For purposes of illustration it is assumed that the parts are so arranged that upon an increase in head pressure the contact member 51 is first moved out of engagement with the contact 58 at 140 pounds and then the contact member 54 is moved out of engagement with the contact 56 at 185 pounds. Upon a decrease in head pressure the contact member 54 first engages the contact 53 at 185 pounds and then the contact member 51 engages the contact 58 at 140 pounds.

The unitary control arrangement 23 also includes a relay or starter generally designated at 60 which may comprise an operating coil 3| for operating bridge members 82 and 63. When the operating coil 6| is energized the bridge member 33 is moved into engagement with contacts l4 and 3! and the bridge member 33 is moved into engagement with contacts '3 and 41. When the operating coil 3| is deenergized the bridge members it and I3 are moved out of engagement with their respective contacts by means of springs, gravity, or other means, not shown. Also included in the unitary control arrangement 33 is an overload cut-out device generally designated at 33. This overload cut-out device is provided with a terminal 10 and a heater element 1| is connected between the terminal 13 and the contact 66. Upon an excess of current flow through the heater element 1| 9. thermostatic element is heated to trip a latch. not shown, for separating

control contacts

13 and 13. The control contacts 12 and 13 may be reclosed by means of a manual reset lever 14. The unitary control arrangement also includes a line terminal 1!. Power is supplied to the compressor motor l4 and to the control system by means of line wires 13 and "leading from some source of power, not shown, the line wire 13 being connected to the contact I. and the line wire 11 being connected to the terminal 13.

with the parts in the position shown in the drawing, the temperature responsive controller 32 is satisfied, the suction pressure is somewhere between 15 pounds and 35 pounds, the head pressure is below 140 pounds and the compressor I3 is not operating. Assume now that the temperature within the compartment ll rises to 42 and that the suction pressure rises to the defrosting value of 35 pounds. Since the head pressure is already reduced to 140 pounds,,a starting circuit is completed from the line wire 13 through contact 33, contact member 34, terminal Bl, wire 33, mercury switch 33, wire 3|, terminal 43, contact member 33, contacts 31 and 33, contact members 4| and I1, cotnact 33, conductor 32, contact 33, conductor 33,

contacts

13 and 13, conductor 34, operating coil 3|, conductor 3!, and terminal 13 back to the other line wire 11. Completion of this starting circuit energizes the operating coil 3| to move the bridge members 33 and 33 into engagement with their respective contacts.

Movement of the bridge member 33 into engagement with the contacts 33 and 31 completes a load circuit for the compressor motor II which may be traced from the line wire 13, through contact 33, conductor 31, terminal 13. heater element 1|, contact 33, bridge member 33, contact 31, wire 33. compressor motor I4, wire 89, and terminal 13 back to the other line wire 11. Completion of this load circuit causes 1 operation of the compressor motor- I4 and hence the compressor l3.

Movement of the bridge member 33 into engagement with the contacts 44 and I completes a maintaining circuit for the operating coil CI of the relay which is independent of the contacts 33 and i3 and the contact members 4| and 51. This maintaining circuit may be traced from the line wire 13 through contact 33, contact member 34, terminal 85, wire 30, mercury switch 33, wire 3|, terminal 43, contact member 33, contact 31, conductor 3|, contact 64, bridge member 63, contact 35, conductor 33, contacts 12 and 13, conductor 34, operating coil 3|, conductor 35, and terminal 15 back to the other line wire 11. Completion of this circuit maintains the operating coil 3| energized and hence the compressor H in operation until either the temperature within the compartment It decreases to 40 or the suction pressure decreases to 15 pounds or the head pressure increases to 185 pounds. When any of these contingencies occur the operating coil 3| of the relay is deenergized and the compressor I9 is stopped. The compressor I3 cannot again be restarted until the starting circuit is again established and this can occur only when the temperature within the compartment I rises to 42 and the suction pressure rises to the defrosting value of 35 pounds and the head pressure decreases to 140 pounds. If an overload condition should occur within the load circuit the overload cut-out 09 operates to separate the contacts 12 and 13 to deenergize the operating coil iii and hence stop operation of the compressor I3.

From the above it is seen that the control arrangement for the compressor I3 operates to maintain the temperature within the compartment I0 between 40 and 42 and loperates to automatically defrost the evaporator II every time that the compressor is shut down since it is impossible to restart the compressor until such time as the suction pressure has risen to the defrosting value of 35 pounds. Starting of the compressor motor against high head pressures is also prevented.

The thermostatic expansion valve I9 which regulates the flow of refrigerant to the evaporator II may comprise a housing I00 having a bottom plate IOI and a top plate I02. Sealed to the bottom plate IN is a bellows I03 which is also sealed to a movable wall I 04. The interior of the bellows I08 is connected by a pipe I05 to a point in the suction line 20 adjacent the outlet of the evaporator II. The bellows I03 therefore forms a pressure operated device for moving the movable wall I04 in accordance with changes in suction pressure at the evaporator outlet and hence in accordance with pressures existing within the evaporator I I. Located between the upper plate I02 and the housing I00 is a cup shaped plate I01 to which is sealed one end of a bellows I08. The other end of the bellows I08 is sealed to the movable wall I 04. A rod I09 is suitably secured to the movable wall I04 and extends upwardly through an opening in the cup shaped plate I01. A bellows ;-IIO is sealed to the cup shaped plate I01 and the rod I09 to seal hermetically the chamber within the bellows I08. The interior of the bellows I08 is connected by a capillary tube III to a bulb II2 which is thermally afi'ected by the temperature of the superheated refrigerant leaving the evaporator II. The bellows I08, the capillary tube III, and the bulb I I2 therefore form an enclosed system which is charged with a volatile fluid so that the bellows Upon an increase in evaporator pressure the movable wall I04 is moved upwardly to close the valve and upon an increase in temperature 'of the superheated refrigerant at the evaporator outlet the movable wall I04 is moved downwardly to open the valve. The spring II4 operates to assist the bellows I03 in moving the movable wall I04 upwardly so that a desired degree of superheat may be maintained at the evaporator outlet. For purposes of illustration, it is assumed that the spring H4 is so adjusted that substantially 8 of superheat are maintained at the evaporator outlet. Therefore the valve is positioned in accordance with the evaporator pressure and the temperature of the refrigerant at the evaporator outlet to maintain a substantially constant superheat of 8 at the evaporator outlet to maintain a desired amount of refrigerant in the evaporator II.

In accordance with the principles of this invention, the enclosed system comprising the bellows I 00, the capillary tube III, and the bulb H2 is charged with a limited amount of volatile fluid so that at some temperature at the evaporator outlet all of the volatile fluid is volatilized and therefore upon an increase in temperature above this value substantially no increase in opening force of the valve is provided. For purposes of illustration it is assumed that the amount of volatile fluid contained in the enclosed system is such that all of the fluid is volatilized when the temperature of the refrigerant leaving the evaporator rises to substantially 33". Therefore for temperatures above 33, no additional opening force is provided. Since the superheat adjustment of the thermostatic expansion valve is such as to maintain a superheat of substantially 8, then when the evaporator pressure increases to a value corresponding to 25, which value for the refrigerant utilized is 25 pounds, it then becomes impossible for the expansion valve to open whenever the evaporator pressure is above 25 pounds. In other words, whenever the evaporator pressure increases above 25 pounds it is impossible for the enclosed system to open the expansion valve.

The volumetric capacity of the enclosed system may be varied to change the temperature value at which the enclosed system becomes inefiective to open the expansion valve and this change in volumetric capacity may be accomplished by connecting the capillary tube I II through a tube I08 forms a pressure operated device for moving wall I04 carries a pin II9 which is located in a slot I20 of a lever I2I which is pivoted at I22. The lever I2I carries a valve element I23 cooperating with a valve seat I24. The valve element I23 and the valve seat I24 form an expansion valve for regulating the flow of refrigerant to the evaporator II.

I26 intoga bellows I21 which is located'in a housing I28. A spring I29 located within the bellows I21 urges the bellows into engagement with an adiusting screw I30. By rotating the adjusting screw I30 the volume in the bellows I21 and therefore the volumetric capacity of the enclosed system may be varied at will. By increasing the volumetric capacity of the control system the temperature at which the enclosed system becomes ineffective to further open the expansion valve may be lowered and by decreasing the volumetric capacity it may be raised. Thus if it be desired to prevent opening of the expansion valve when the evaporator pressure increases above 25 pounds corresponding to a 25 evaporator temperature and if the spring H4 is adjusted to give a 10 superheat in place of the 8 superheat referred to above, then the volumetric capacity of the enclosed system may be changed to render the enclosed system inefiective to further open the valve when the temperature of the superheated refrigerant leaving the evaporator rises to 25 plus 10 or 35.

From the above it is seen that I have provided a control system for a refrigerating apparatus wherein the compressor which circulates refrigerant through the evaporator is stopped for the purpose of defrosting the evaporator and wherein it is impossible to open the expansion valve during this defrosting period whenever the evaporator pressure rises above a predetermined value which corresponds to a temperature value below freezing. Thus defrosting of the evaporator is hastened and the evaporator pressure will at all times correspond to the temperature of the evaporator so that at any temperature above freezing, that is, at any defrosting temperature the valve will be closed. It will therefore be impossible to restart the refrigerating apparatus until after the evaporator has actually defrosted since no refrigerant will be allowed to leak into the evaporator during the defrosting cycle to raise the pressure in the evaporator to the defrosting value before the evaporator has actually been defrosted.

Although for purposes of illustration one form of this invention has been disclosed, other forms thereof may become apparent to those skilled in the art upon reference to this disclosure and therefore this invention should be limited only by the scope of the appended claims.

I claim as my invention:

1. In combination, an evaporator for cooling a medium, means for circulating refrigerant through the evaporator and normally to reduce the evaporator pressure to a value which reduces the evaporator temperature below freezing, means for interrupting operation of the circulating means to allow the evaporator pressure to increase to a value corresponding to a temperature value above freezing for defrosting the evaporator, and valve means for regulating the flow of refrigerant to the evaporator for maintaining a desired amount of refrigerant in the evaporator while the circulating means is operating, said valve means including mechanism for positively preventing flow of refrigerant to the evaporator when the evaporator is defrosting.

2. In combination, an evaporator for cooling a medium, means for circulating refrigerant through the evaporator and normally to reduce the evaporator pressure to a value which reduces the evaporator temperature below freezing, means for interrupting operation of the circulating means to allow the evaporator pressure to increase to a value corresponding to a temperature value above freezing for defrosting the evaporator, and an expansion valve for regulating the flow of refrigerant to the evaporator for maintaining a desired amount of refrigerant in the evaporator while the circulating means is operating and for positively preventing flow of refrigerant to the evaporator when the evaporator pressure is above a predetermined value corresponding to a temperature value below freezing.

3. In combination, an evaporator for cooling a medium, means for circulating refrigerant through the evaporator and normally to reduce the evaporator pressure to a value which reduces the evaporator temperature below freezing, means for interrupting operation of the circulating means to allow the evaporator pressure to increase to a value corresponding to a temperature value above freezing for defrosting the evaporator, and-a thermostatic expansion valve for regulating the flow of refrigerant to the evaporator for normally maintaining a desired amount of refrigerant in the evaporator while the circulating means is operating, said thermostatic expansion valve including means operated in accordance with the evaporator pressure for increasing the supply of refrigerant to the evaporator upona decrease in pressure and means operated in accordance with the temperature of the superheated refrigerant at the evaporator outlet for increasing the supply of refrigerant to the evaporator upon an increase in temperature, said thermostatic expansion valve being so arranged as to positively prevent the flow of refrigerant to the evaporator while the evaporator pressure is high enough for defrosting.

4. In combination, an evaporator for cooling a medium, means for circulating refrigerant through the evaporator and normally to reduce the evaporator pressure to a value which reduces the evaporator temperature below freezing, means for interrupting operation of the circulating means to allow the evaporator pressure to increase to a value corresponding to a temperature value above freezing for defrosting the evaporator, and a thermostatic expansion valve for regulating the flow of refrigerant to the evaporator for normally maintaining a desired amount of refrigerant in the evaporator while the circulating means is operating, said thermo-,

static expansion valve including means operated in accordance with the evaporator pressure for increasing the supply of refrigerant to the evaporator upon a decrease in pressure and means operated in accordance with the temperature of the superheated refrigerant at the evaporator outlet for increasing the supply of refrigerant to the evaporator upon an increase in temperature, said thermostatic expansion valve being so arranged as to positively prevent the flow of refrigerant to the evaporator when the evaporator pressure is above a value corresponding to a temperature value below freezing.

5. In combination, an evaporator for cooling 9. medium, means for circulating refrigerant through the evaporator and normally to reduce the evaporator pressure to a value which reduces the evaporator temperature below freezing,

means for interrupting operation of the circulating means to allow the evaporator pressure to increase to a value corresponding to a temperature value above freezing for defrosting the evaporator, an expansion valve for regulating the flow of refrigerant to the evaporator for maintaining a desired amount of refrigerant in the evaporator while the circulating means is operating, and means associated with the expansion valve for causing the valve to positively prevent flow of refrigerant to the evaporator when the evaporator is defrosting.

6. In combination, an evaporator for cooling a medium, means for circulating refrigerant through the evaporator and normally to reduce the evaporator pressure to a value which reduces the evaporator temperature below freezing, means for interrupting operation of the circulating means to allow the evaporator pressure to increase to a value corresponding to a temperature value above freezing for defrosting the evaporator, an expansion valve for regulating the flow of refrigerant to the evaporator for maintaining a desired amount of refrigerant in the evaporator while the circulating means is operating, and means whereby the expansion valve prevents flow of refrigerant to the evaporator when the evaporator pressure is above a predetermined value corresponding to a temperature value below freezing.

"I. In combination, an evaporator for cooling a medium, means for circulating refrigerant sion valve including means operated in accordance with the evaporator pressure for increasing the supply of refrigerant to the evaporator upon a decrease in pressure and means operated in accordance with the temperature of the superheated refrigerant at the evaporator outlet for increasing the supply of refrigerant to the evaporator upon an increase in temperature, and means associated with the thermostatic expansion valve for preventing flow of refrigerant to the evaporator when the evaporator is defrosting.

8. In combination, an evaporator for cooling a medium, means for circulating refrigerant through the evaporator and normally to reduce the evaporator pressure to a value which reduces the evaporator temperature below freezing, means for interrupting operation of the circulating means to allow the evaporator pressure to increase to a value corresponding to a temperature valu above freezing for defrosting the evaporator, a thermostatic expansion valve for regulating the flow of refrigerant to the evaporator for normally maintaining a desired amount of refrigerant in the evaporator while the circulating means is operating, said thermostatic expansion valve including means operated in accordance with the evaporator pressure for increasing the supply of refrigerant to the evaporator upon a decrease in pressure and means operated in accordance with the temperature of the superheated refrigerant at the evaporator outlet for increasing the supply of refrigerant to the evaporator upon an increase in temperature, and means associated with the thermostatic expansion valve for preventing flow of refrigerant to the evaporator when the evaporator pressure is above a predetermined value corresponding to a temperature value below freezing.

9. In combination, an evaporator for cooling a medium, means for circulating refrigerant through the evaporator and normally to reduce the evaporator pressure to a value which reduces the evaporator temperature below freezing, means for interrupting operation of the circulating means to allow the evaporator pressure to increase to a value corresponding to a temperature value above freezing for defrosting the evaporator, a thermostatic expansion valve for regulating the flow of refrigerant to the evaporator for normally maintaining a desired amount of refrigerant in the evaporator while the circulating means is operating, said thermostatic expansion valve including means operated in accordance with the evaporator pressure for increasing the supply of refrigerant to the evaporator upon a decrease in pressure and means operated in accordance with the temperature of the superheated refrigerant at the evaporator outlet for increasing the supply of refrigerant to the evaporator upon an increase in temperature, said temperature operated means of the thermostatic expansion valve being so arranged as to be effective to prevent the supply of refrigerant to the evaporator when the evaporator pressure is above a predetermined value corresponding to a temperature value below freezing.

10. In combination, an evaporator for cooling a medium, means for circulating refrigerant through the evaporator and normally to reduce the evaporator pressure to a value which reduces the evaporator temperature below freezing, means for interrupting operation of the circulating means to allow the evaporator pressure to increase to a value corresponding to a temperature value above freezing for defrosting the evaporator, and a thermostatic expansion valve for regulating the flow of refrigerant to the evaporator for normally maintaining a desired amount of refrigerant in the evaporator while the circulating means is operating, said thermostatic expansion valve including means operated in accordance with the evaporator pressure for increasing the supply of refrigerant to the evaporator upon a decrease in pressure and means opposing said last means operated in accordance with the temperature of the superheated refrigerant at the evaporator outlet comprising an enclosed system charged with a limited amount of volatile fluid for increasing the supply of refrigerant to th evaporator upon an increase in temperature said fluid being of such amount as to become completely vaporized when the evaporator pressure is above a value corresponding to a temperature value below freezing whereby said temperature operated means develops no appreciable further pressure as the temperature of super-heated refrigerant increases and said pressure operated means keeps the valve positively closed as the evaporated temperature increases.

11. In combination, an evaporator for cooling a medium, means for circulating refrigerant through the evaporator and normally to reduce the evaporator pressure to a value which reduces the evaporator temperature below freezing, means for interrupting operation of the circulating means to allow the evaporator pressure to increase to a value corresponding to a temperature value above freezing for defrosting the evaporator, a thermostatic expansion valve for regulating the flow of refrigerant to the evaporator for normally maintaining a desired amount of refrigerant in the evaporator while the circulating means is operating, said thermostatic expansion valve including a valve for regulating the supply of refrigerant to the evaporator, pressure operated means responsive to the evaporator pressure for closing the valve upon an increase in pressure, and pressure operated means comprising an enclosed system charged with a limited amount of volatile fluid and responsive to the temperature of the superheated refrigerant at the evaporator outlet for opening the valve the amount of fluid being such that it becomes completely vaporized at a predetermined temperature of the superheated refrigerant whereby no appreciable further valve opening pressure is developed so that the valve remains positively closed as the evaporator pressure increases.

12. In combination, an evaporator for cooling a medium, means for circulating refrigerant through the evaporator and normally to reduce the evaporator pressure to a value which reduces the evaporator temperature below freezing, means for interrupting operation of the circulating means to allow the evaporator pressure to increase to a value corresponding to a temperature value above freezing for defrosting the evaporator, a thermostatic expansion valve for regulating the flow of refrigerant to the evaporator for normally maintaining a desired amount of refrigerant in the evaporator while the circulating means is operating, said thermostatic expansion valve including a valve for regulating the supply of refrigerant to the evaporator, pressure operated means responsive to the evaporator pressure for closing the valve upon an increase in pressure, pressure operated means comprising an enclosed system charged with a limited amount of volatile fluid and responsive to the temperature of the superheated refrigerant at the evaporator outlet for opening the valve the amount of fluid being such that it becomes completely vaporized at a predetermined temperature of the super-heated refrigerant whereby no appreciable further valve opening pressure is developed so that the valve remains positively closed as the evaporator pressure increases, and means for adlusting the volumetric capacity of the enclosed system to vary the evaporator conditions under which the valve remains fully closed.

13. A thermostatic expansion valve for a refrigerating apparatus having an evoparator and means for circulating refrigerant through the evaporator to be evaporated therein, comprising in combination, a valve for regulating the supply of refrigerant to the evaporator, pressure operated means responsive to the evaporator pressure for closing the valve upon an increase in pressure, pressure operated means including an enclosed system charged with a limited amount of volatile fluid and responsive to the temperature of the superheated refrigerant at the evaporator outlet for opening the valve upon an increase in pressure, the amount of fluid being such that it becomes completely vaporized at a predetermined value of the super-heated refrigerant whereby no appreciable further valve opening pressure is developed so that the valve remains positively closed as the evaporator pressure increases, and means for adjusting the volumetric capacity of the enclosed system to vary the value of the evaporator pressure at which opening of the valve is prevented.

14. In combination, an evaporator for cooling a medium, means for circulating refrigerant through the evaporator and normally to reduce the evaporator pressure to a value which reduces the evaporator temperature below freezing, means for interrupting operation of the circulating means to allow the evaporator pressure to increase to a value corresponding to a temperature value above freezing for defrosting the evaporator, means responsive to evaporator pressure to allow restarting of the circulating means only when the evaporator pressure rises to a value corresponding to a temperature value above freezing, and an expansion valve for regulating the flow of refrigerant to the evaporator for maintaining a desired amount of refrigerant in the evaporator while the circulating means is operating and said expansion valve having structural characteristics whereby flow of refrigerant to the evaporator is positively prevented when the evaporator pressure is above a value corresponding to a temperature value below freezing.

15. In combination, an evaporator for cooling a medium, means for circulating refrigerant through the evaporator and normally to reduce the evaporator temperature below freezing, means for interrupting operation of the circulating means to allow the evaporator pressure to increase to a value corresponding to a temperature value above freezing for defrosting the evaporator, means responsive to evaporator pressure to allow restarting of the circulating means only when the evaporator pressure rises to a value corresponding to a temperature value above freezing, and a thermostatic expansion valve for regulating the flow of refrigerant to the evaporator for normally maintaining a desired amount of refrigerant in the evaporator while the circulating means is operating, said thermostatic expansion valve including means operated in accordance with the evaporator pressure for increasing the supply of refrigerant to the evaporator upon a decrease in pressure and means operated in accordance with the temperature of the superheated refrigerant at the evaporator outlet for increasing the supply of refrigerant to the evaporator upon an increase in temperature, said thermostatic expansion valve embodying means so arranged as to prevent the flow of refrigerant to the evaporator when the evaporator pressure is above a value corresponding to a temperature value below freezing.

16. In combination, an evaporator for cooling a medium, means for circulating refrigerant through the evaporator and normally to reduce the evaporator pressure to a value which reduces the evaporator temperature below freezing, means for interrupting operation of the circulating means to allow the evaporator pressure to increase to a value corresponding to a temperature value above freezing for defrosting the evaporator, and control means for regulating the flow of refrigerant to the evaporator for maintaining a desired amount of refrigerant in the evaporator while the circulating means is operating, said control means including mechanism responsive to a condition which is a measure of evaporator temperature for positively preventing flow of refrigerant to the evaporator when its temperature exceeds a predetermined value.

17. In combination, an evaporator for cooling a medium, means for circulating refrigerant through the evaporator and normally to reduce the evaporator pressure to a value which reduces the evaporator temperature below freezing. means for interrupting operation of the circulating means to allow the evaporator pressure to increase to a value corresponding to a temperature value above freezing for defrosting the evaporator, and control means for regulating the flow of refrigerant to the evaporator for maintaining a desired amount of refrigerant in the evaporator while the circulating means is operating, said control means including mechanism responsive to a condition which is a measure of evaporator temperature for positively preventing flow of refrigerant to the evaporator when its temperature exceeds a predetermined value, and means operative at a predetermined value of evaporator pressure representative of a relatively high temperature for causing the circulating means to start, said mechanism for positively preventing admission of refrigerant to the evaporator serving to avoid delay in the evaporator pressure rising to said predetermined value when the circulating means are not operating.

18. In combination, an evaporator for cooling a medium, means for circulating refrigerant through the evaporator and normally to reduce the evaporator pressure to a value which reduces the evaporator pressure to a value which reduces the evaporator temperature below freezing, means for interrupting operation of the circulating means to allow the evaporator pressure to increase to a value corresponding to a temperature value above freezing for defrosting theevaporator, and control meansfor regulating the flow of refrigerant to the evaporator for maintaining a desired amount of refrigerant in the evaporator while the circulating means is operating, said control means including mechanism responsive to a condition which is a measure of evaporator temperature for positively preventing flow of refrigerant to the evaporator when its temperature exceeds a- "predetermined value, said control meansand mechanism comprising an expansion valve and an enclosed system having a thermal bulb containing a limited amount of volatile liquid, the bulb being thermally associated with the evaporator, the amountof'liquid being such as to be completely vaporized at a predetermined temperature so as to develop no appreciably further pressure at higher temperature, and said expansion valve being of a type responsive to evaporator pressure and to said bulb wherein for interrupting operation of the circulating means to allow the evaporator pressure to increase to a value corresponding to a temperature value above freezing for defrosting the evaporator, and control means for regulating the flow of refrigerant to the evaporator for maintaining a desired amount of refrigerant in the evaporator while the circulating means is operating, said control means including mechanism responsive to a condition which is a measure of evaporator temperature for positively preventing flow of refrigerant to the evaporator when. its temperature exceeds a predetermined value, said control means and mechanism comprising an expansion valve and an enclosed system having a thermal bulb containing alimited amount of volatile liquid, the bulb being thermally associated with the evaporator, the amount of liquid being such as to be completely vaporized at a predetermined temperature so as to develop no appreciably further pressure at higher temperature, and said expansion valve being of a type responsive to evaporator pressure and to said bulb wherein evaporator pressure urges the valve in closing direction and pressure in said bulb urges the valve in opening direction so that if the evaporator pressure increases after the pressure in the bulb reaches its maximum the valve is held positively closed, and means responsive to evaporator pressure arranged to start the circulating means at a predetermined value thereof.

20. In combination, an evaporator for cooling a medium, means for circulating refrigerant through the evaporator and normally to reduce the evaporator pressure to a value which reduces the evaporator temperature below freezing, means for interrupting operation of the circulating means to allow the evaporator pressure to increase to a value corresponding to a temperature value above freezing for defrosting the evaporator, and control means for regulating the flow of refrigerant to the evaporator for maintaining a desired amount of refrigerant in the evaporator while the circulating means is operating, said control means including mechanism responsive to a condition which is a measure of evaporator temperature for positively preventing flow of refrigerant to the evaporator when its temperature exceeds a predetermined value, said control means and mechanism comprising an expansion valve and an enclosed system having a thermal bulb containing a limited amount of volatile liquid, the bulb being thermally associated with the evaporator, the amount of liquid being such as to be completely vaporized at a predetermined temperature so as to develop no appreciably further pressure at higher temperature, and said expansion valve being of a type ,responsive to evaporator pressure and to said bulb wherein evaporator pressure urges the valve in closing direction and pressure in said bulb urges the valve in opening direction so that if the evaporator pressure increases after the pressure in the bulb reaches its maximum the valve is held positively closed, and means for adjusting the volumetric capacity of said enclosed system.

21. In apparatus of the character described, in combinatio n, an expansion valve for controlling a volatile fluid, means responsive to pressure of fluid after it has passed through said valve for urging the valve in closing direction, means for urging the valve in opening direction against the force of said first means, said second means comprising an enclosed system including a thermal bulb filled with a limited amount of volatile liquid, said bulb being positioned so as to respond to the temperature of said fluid after passing through the valve, the amount of said liquid being such that it becomes completely vaporized at a predetermined temperature of said fluid so that noappreciable further pressure is developed in said enclosed system and further increases in pressure of said fluid beyond the valve positively hold it in closed position;

22. In apparatus of the character described, in combination, a thermostatic expansion valve having means comprising an enclosed system having a thermal bulb filled with a limited on the valve as the temperature increases, means for exerting a variable closing force balancing said first force on the valve, whereby if said closing force increases after said predetermined temperature is reached the valve is closed and held firmly closed. ALWIN B. NEWTON.