US2313391A - Refrigerating system - Google Patents

Description

March 9, 1943. A. B. NEWTON 2,313,391

REFRIGERATING SYSTEM le. 2; 26o srwentor 206 Alwi'm. Newi-ol/L.

FROM

Glforngg CONDENSER.

March 9, 1943- A. B. NEWTON REFRIGERATING SYSTEM 2 Smets-sheer 2 Filed Sept. 28, 1940 Clikorne'g fnventor Alwin.. Newham.-

EP//yre I coMPREssoR.

mom coNoENsER.

Patented Mar. 9, 1943 UNiTi-:n 'STATES PATENT OFFICE 2,313,391 REFaIGEmA'rmG SYSTEM Alwin B. Newton, Minneapolis, Minn., assigner to Minneapolis-Honeywell Regulator Company,

Minneapolis, Minn., a corporation of Delaware Application September 28, 1940, Serial No. 358,781

12 claims. (cl. s2-s) 'I'he present invention relates to refrigeration, more particularly to systems of the .compression type and it is especially concerned with improved means for preventing high evaporator pressures and consequent heavy loads on the compressor.

The invention disclosed herein is an improvement of the refrigerating systems having superheat control disclosed in my prior applications as follows: Serial No. 243,843 led December 3,

1938; Serial No. 286,594, led July 26, 1939, and Serial No. 300,400 led October 20, 1939. My prior applications show various arrangements for controlling the .superheat at the outlet of an evaporator. Thesearrangements include superheat valves having an equalizer connection, which is a pipe for communicating pressure to the pressure responsive element of the valve, and which may be connected tothe evaporator at points having diierent preures to vary the `superheatl to be maintained. These prior arrangements also-'comprehend a pressure operated expansion valve controlled by a small pilot valve which may be responsive to temperature orv superheat.

My present invention comprehends the provision of an additional small valve responsive to evaporator pressure which may be located in the I designates generally the compressor of a compression type refrigeration system. The com presser is driven by an electric motor` II-through a belt I2. The compressor discharges through a pipe I3 into a condenser. I4 of usual type. 'I'he condenserJ is connected bya pipe I5`to an expansion valve I6 of the superheat control type and the outlet of the expansion valve I6 is connected to an evaporator coil I1 by a pipe I8. 'Ihe outlet of the evaporator coil I1 is connected to the suction side of the compressor by a pipe I9.

which controls the compressor motor II through equalizer connection or may act as a supplemental i pilot valve to cause the main valve to restrict the flow of refrigerant to the evaporator when evap- I orator pressure is relatively high, that is' under 4heavy load conditions, to avoid placing unduly great loads on the compressor. This additional valve is ltherefore normally inactive, its object being to control the pressure acting on the main 'valve so as to cause the main valveto move toward closed position when the evaporator pressure rises to relatively high values for the reason .iust pointed out. In this way a very small valve may be used to limit the load placed on thecompressor but which valve is inoperative to increase the rate of refrigerant supply beyond the demands of the valves normally vin control.

For a complete understanding of my invention and appreciation of the specic manner of attainmentof its objects and advantages, reference may be had to the following detailed description and annexed drawings wherein: Figure. 1 represents diagrammatically a refrigthe wires 26, 21 and28. The operation of the controller 23 isto start the compressor at a predetermined high suction pressure and to stop it at a predetermined relatively lower suction pressure and also to shut down' the compressor in the event of occurrence of a relatively high head or discharge pressure.

'I'he evaporator coilv II forms part of -an air conditioning unit designated generally at 30, the

unit 30 comprising a longitudinal passageway for f air having openings 3I and 32 kat its lower portion whereby fresh and recirculated air may be' admitted in regulatable quantities for passage over the coil I1. The proportions of /fresh andl recirculated. air may be varied by adjustment of' eratingsystem embodying one form of my invention;

Figure Z-represents a modiiiedform of the invention, and

Figure 3 representsv a second modified form ofl thejnvention.

Referring to Figurel of the drawings, numeral 55 -lfrom the compressor is connected.

a damper 33.' A continuous circulation of val1' may be enforced through the unit 30 by means of a motor driver fan 34. f

'Ihe expansion valve I6 includes ya body 35 havingan inlet chamber 36- to which the pipe I5 Within the. body ofthe valve is a longitudinal throat 31 the lower end of'whichforms a seat `for a valve member 38. The pipe I8 leading to the evaporator I'I is connected to an intermediate portion v:if/the throat 31. The upper part of the valve body 3l forms a chamber 39Awhich is sealed by a iexible diaphragm 40, the edges of which engage a ilange 4I at the upper part of the valve body,theedg'es p f the diaphragm being secured between` the iiange 4i and ya .ilange 42 on a bulgedvalve cover I3, the cover being secured to the valve body in any -perature responsive suitable manner.

stem, one end of which is connected to the valve which normallyurges the valve stem in an upward direction so as to urge the valve member 38 against its seat. Numeral 48 designates suitable packing around the valve stem 44 between ring 45 and the upper end of throat 31.

, The spacebetween the valve cover 43 and the diaphragm 40 is connected to a temperature responsive bulb 58 filled with volatile liquid by means of a tube 5I. The bulb 50 is disposed in intimate thermal contact with the outlet of the evaporator coil I1 so as to be responsiveto the temperature thereof. The liquid in the bulb 50 vaporizes and develops a. pressure proportional to the temperature at the evaporator outlet which is communicated to the chamber on the upper side of diaphragm 40 by tube 5I and acts to urgethe diaphragm downwardly.

Pressure on the downstream side of the valve I6 may pass throughthe packing 48 and ring 45 around the valve stem and into the chamber 39 below the diaphragm 40 so that the lower side of the diaphragm is exposed to pressure within the upper part of the body of the expansion valve. Packing 48 of course limits the ow of refrigerant into chamber 39.

The expansion valve structure as so far described corresponds to superheat control valves well known in the art wherein evaporator pressure acts to urge-the expansion valve in closing direction and a pressure corresponding to the temperature of superheated refrigerant at the outlet of the evaporator tends to urge the valve in opening direction. The arrangement of my invention however includes additional structure which will now be described.

Numeral 55 designates a pipe leading from the chamber 39 of valve I6 to a control valve 56. The outlet of the control valve 56 is connected to an additional control valve 51 by a pipe 58 and the outlet of the valve 51 is connected to the suction pipe I9, that is, the pipe leading from the outlet of the evaporator coil I1, by'a pipe 59. The connections from the chamber 38 of valve I6 to the evaporator outlet form an equalizer connection for the expansion valve I6 which in itself is a structural detail known in theA art.

The valve 56 comprises a casing 60 having an internal partition 6I which has an opening therethrough forming" afvalve 'seat for a valve member 62. The upper part of the casing 6811s closed by a suitable member 63 and the stem ,64 of the valve member 62 extends throughthe member 63 and is connected to a collapsible bellows 65, one end of which is secured tol theA member 63. Within the bellows 65 is a coil spring 66 which acts against the bellows 65 to expand it and to urge the valve stem 64 in closing direction of the valve. On the exterior of the bellows 65 is a knob 61 against which bears a cam 68 which is in the form of an eccentric disk driven by a proportioning motor 69 of the type disclosed in detail in the patent of D. G. Taylor N-o. 2,028,110.

The proportioning motor69 is supplied with velectrical power by wires 18 land 1` I and is controlled by a proportioningcontroller. designated at 12.

The proportioning controller comprises a tembellows 13 llled with a vola- L through the pipe 59 the temperature at bulb 58. 'I'here is a given Y Numeral 44 designates a valve tile liquid so that it expands and contracts in accordance with the temperature affecting the bellows. The bellows has a stem at its movable end which bears against a pivoted arm 14 which forms a slider cooperating with an electric resistance 15. A coil spring 16 normally urges the:`

arm 14 in a counter-clockwise.direction The ends of the resistance 15 are, connected to the proportioning ymotor 69 by wires 11 and 18 and the arm 14 is connected to the proportioning motor by a wire 19. When the temperature is above a predetermined value, the slider 14 is at the upper end of the resistance 15 as shown on th'e drawing and the valve 56 is wide open under these circumstances. When the temperature affecting the controller 12 falls below a predetermined value the slider 14 moves downwardly over the resistance 15 causing the motor 69 to operate in a direction to rotate the cam 68 so that it permits the bellows 65 to expand, moving the valve member 62 towards its seat. AsA the temperature alecting the controller 12 falls, the valve 56 continues to close and becomes fully closed at a predetermined temperature alecting the controller 12, the operation of the proportioning motor 69 in response to the controller 12 being the same as that described in det-ail in the above referred to Taylor patent.

The valve 51 comprises a casing 88 having an internal partition 8l with an opening therethrough forming a valve seat for a valve member 82. The upper part of the casing is closed by a suitable member 83 having an opening therethrough, through which extends a stem 84 connected to the valve member 82, the upper end of the stem 84 being connected to a collapsible bellows 85 corresponding tothat of the valve 56. The bellows 85 has a knob 86 at its movable end anda pivoted lever arm 81 normally engages this knob, the lever arm 81 being pivoted to an arm 88 at one end and being connected at its other end to a coil spring 89 which normally urges the lever 81 in a counter-clockwise direction tending to'collapse the bellows 85 and urge the valve member 82 away from its seat. Pressure from within the evaporator coil I1 is free to pass `into the casing 88 and through the closure member 83 around the valve stem to the interior of the bellows 85. When the pressure within the bellows 85 builds up sufciently, it is operative to expand the bellows 85 against the force of spring 89 so as to move the valve member 82 against its seat, that is, to closed position.

When the control valves 56 and 51 are in open position there is free communication between the chamber 39 of valve I6 and the outlet of the evaporator and under these circumstances the expansion valve I6 functions in a known manner to maintain a constant degree of superheat at the outlet of the evaporator by maintaining a constant dilerence between the vpressure in chamber 39 and the pressure corresponding to pressurfdrop through the evaporator coil I1 and with the interior of the chamber 39 in free communication with the oultet ofthe evaporator the r pressure within chamber 39 is lower than it would be if this chamber were exposed to pressure at.

the inlet of the evaporator. The packing 48 permits a slight amount of leakage around the valve stein 44 from the evaporator inlet into chamber 39 and the equalizer connection. Thus normally there is a small flow of refrigerant from the evaporatorl inlet through the equalizer connection through fthe/evaporator outlet. 4connectiontherefore forms a bleed circuit from the chamber 39 and the function of the control lvalve 58 is toclose oi! the equalizer connection progressively in response to falling temperature aiIeJctl/ng.,v the controller 12 so that as valve 58 closes there is more and more restriction in the equalizer connection causing refrigerant from theinlet of the evaporator to accumulate under- 'neath the diaphragm and to build up a pressure tending to urge valve," I8' in closing direction. l,/rll'hus as valve 58 moves towards closed position valve I8 also moves. towards closed position so that refrigerant is admitted to the evaporator at a lower ratel and a relatively higher degree of superheat is maintained at the outlet of the evaporator. In other-words, the controller 12 and control' valve 58 act to control the refrigerating capacityof the eva-porating'coil I1; i

In-systems of the type. disclosed wherein the capacity of the evaporator is controlled by controlling the 'superheat' at the outlet of the 'evaporator, there may be times when the coolingloadl Ais relative/ly heavy and under these conditions theV evaporator pressure may rise to a relatively high value. Under these circumstances, the

$3,813,891: The equalizer `:s branch pipe1203 connected to the pipe l5. The chamber communicates with the inlet side .of lthe valve 82 by means of'a chanel 204 having a metering oriiice member 205 at its lower end'.

'I'he pipe 55 from-the valve I6 is connected to the l channel 204. Numeral 206 designates a filtering screen within the chamber 20|. 4From the fore,

going, )it will be apparent that. high pressure refrigerant may .be'bled through themetering orice member 205 into the equalizer connections `so that when either of the control valves in the equalizer connection is closed, high pressure refrigerant will bleed through the metering orice and pipe 55 into the chamber below the diaphragm of valve I8 so as to fully close the valve.

. This arrangement is described lin detail in my compressor is withdrawing relatively dense re- ,frigerant from the evaporator at relatively high pressure, or ,in other words, it is withdrawing 'a relatively large weight of refrigerantethat is, the

compressor is pumping refrigerant at a high rate such that the compressor motor may becomeoverloaded.` Under these circumstances, it is desirable to provide means for reducing the evaporator pressure by restricting the rate of admission of "refrigerant to the evaporator. To

provide `lor securing this result, the control valve 81 moves towards closed position when the evaporatoipressure rises` to a predetermined value ,at which the bellows 85 is expanded, overcoming the spring 89. As the control valve 51- closesiit cuts 0E the equalizer connection in the same manner as .the control valve 56 does when it closes. 'I'he effect of to cause the pressure to build up underneath the diaphragm 40, in the same manner as when the control valve 88 closes.4 Thus under heavy load conditions when the compressor-motor may become overloaded, the expansion valve is moved towards a fully restricted condition so as to decrease the rate of admission of-refrigerant to the evaporator .coil so that a relatively higher degree of superheat isfmaintain'ed at the outlet. In this manner, a very small and inexpensive valve may be employed to prevent the compressor motor from becoming overloaded by reducing the rate of admission of refrigerant to the evaporator coil.

This valve under normaloperating conditions' is open and does not interfere with the superheat control valve or the control by the temperature responsive controller 12. y

. Referring to Figure 2 of the drawings, the system is essentially the same as that of Figure 1, e like numerals designating like elements in the two figures. The embodiment of Figure 2 may ,include the compressor, condenser, and controller 23 of Figure l, these parts of the system not being shown on Figure 2. The control valve 256 of Figure` 2 is like the valve 56 of Figure l except that it provides for'rnetering refrigerant from the'high side of the system into theequalizer connection. Its casing 280 has an internalchamber 20| and the lower `part of the casing 280 is closed by amember 202. 'Ihe chamber 20| isin compriory application referred to above Serial No. 286,594, filed July 26,' 1939. `In some systems the pressure drop through the evaporator may not be suicient to provide for c'omplete modulation of the expansion valve, that is to fully closed posi- The control valve 251 of the present embodiment corresponds to the valve 51 of the previous embodimentv and operates in the same manner. Y

However, in the present embodiment there is a coil spring 2|0 within the bellows 85 which urges the bellows in opening direction of the valve.4 f A lever 281 is pivotedgnear its mid point, one end -end of the lever bearing against the knob 88 of the bellows and the other end of the bellows being urged in aA counter-clockwise direction'by the coil Aspring 89. Numeral 2li designates a pressure responsive bellows, the interior of which is connected to the suction pipe I0 by a pipe 2I2. 'I'he movableend of the bellows 2li carries a stem acting on the lever arm 281 urging it in a counter-clockwise direction tending to collapse the bellows 05 so as to move the valve lin closing direction. Similarly to the operation in the pre(- vious embodiment when the pressure .within the evaporator and Within the pipe I 9 rises to a relatively high value', the bellows 2|I expands 4collapsing the bellows 85 and moving the valve 251 to closed'position. I

The operation of the embodiment vof Figure 2 is the same as that of Figure 1v except for the differences pointed out above. Whenever either of the control valves 256 or 251 is fully closed, flow through the equalizer connection is cut 01T` entirely. Under these circumstanceathe lower side of the diaphragm within the expansion valve I8 is subjected to the pressure of the high side refrigerant .bled through the metering orifice member 205 and through the pipe 55, This high pressure refrigerant accumulating within the chamber 39 serves to fully vclose the expansion valve. When the ow through the equalizer connection is modulated by either of the control valves, higher pressure is available for closing the expansion valve I6 than is available in the arrangement of Figure 1 wherein high s idrel frigerant is not metered into the equalizer con-f nection. As pointed out in my prior applications,

thearrangement of Figure 2 provides for moduv lation from'zeropercent to' one hundred percent capacity'of the evaporator coil while with the arrangement of Figure l normally modulation munication with the condenser by means o f a 7.5l

from approximately'iiqper cent to 100 per cent of coil capacity only may be obtained. In Flgure 2, as in Figure 1, -when\t-he evaporator pressure rises above a predetermined relatively high value the valve 251 cuts off low through the equalizer connection 'causing the expansion valve to move towards fully restricting position so that previous embodiments but which have not been Cil therewithin and accordingly moving the valvel head 326 toward -or away from its seat. A cap` 335 engages the nipple 3|4 in screw-threaded relationship Iexterior of the casing 306 and a bleed `pipe 336 is connected to the cap 335. The pipe 336 is connected to a pilot valve 331 which, as

- presently described is of the superheat control type.' The outlet of the valve 331 is connected by a pipe 338 witha control valve 56 which is the same as the valve 56 of the previous embodiments. The outlet of the valve 56 is connected shown on Figure 3, the outlet of the condenser v being connected to av pressure operated expansion valve 30| by a pipe 302. The outlet of the expansion valve 30| is connected to an evaporator |1 by a pipe 303 and the evaporator has an outlet pipe 304 which is connected to the suction side of the compressor. A portion 305 of the outlet pipe of the evaporator is shown enlarged for purposes which will presently become apparent.

The expansion valve comprises a generally cylindrical casing 306, the lower part of which is closed by a plate 301, there being va gasket '308 interposed between the plate 301 and the'adjacent portions of the casing 306 so as to make the interior of the casing 306 fluid tight. The plate 301 has suitable ears as shown at 309 through 'whichextend hook bolts 3|'0 and 3|| having hooks which engage the upper part of the casing 306 and which have nuts 3|2 and 3|3 engaging their opposite ends. Numeral 3|4 designates a screw-threaded nipple, member which engages the central part of the plate 301 in screw-thread ed relationship. The portion of the nipple 3|4 2 within the casing 306 is of slightly larger diameter and it has an annular grooove 3|5 communicating with a longitudinal oriiice 3|6 in the nipple 3|4 by means of a transverse channel orice 3|1. Secured to the'portion of nipple 3|4 within the casing 306 is an expansible and contractable cell 320 formed by two flexible diaphragms' 32| and 322 secured together at their edges. Within the cell 320 is a metal disk 323 of'suitable thickness to prevent the cell from completely collapsing so as to avoid overstressing of the diaphragms. disk 323 and the upper diaphragm 32| is a spring member324 in the form of a spider having a number of ngers which normally urges the cell into expanded position. Secured to the upper diaphragm 32|,is a disk 325 having a stud to which is secured a valve head 326. The valve 'head 326 cooperates with a seat formed by a rounding the portion of the nipple 3|4 within: the casing 306 `and covering the groove 3|5 so that refrigerant entering the groove 3|5 must pass through the screen. Numeral 33| designates a ringeshaped screen member disposed within the casing 306 so that refrigerant entering through the inlet pipe 302 must pass through the screen 33| before it cancome in contact .with the cell 320.

Refrigerant which enters the casing 306 is free to pass'through the groove 3|5 .and the orifices 3|1 and 3I6 to the interior of the cell 320 and the cell 320 expands and contracts in accordance Interposed between the with the pressure of the refrigerant developed to a control valve 51 which is the same as the valve 51 of the previous embodiment by a pipe 339. The .outlet of the valve 51 is connected to an intermediate point of the evaporator il by a pipe 340. As shown on the drawing, the pipe 340 is connected to one of the last passes of the evaporator I1 but it is to be understood that it might be connected to other intermediate points of the evaporator or to the outlet.

From the foregoing, it is apparent that high pressure refrigerant is metered into the interior of the cell 320 and that this refrigerant is bled oi y from the interior of the cell through the control valves` 331, 56 and 51 to the evaporator |1. The valves 56 and 51 operate to control the bleed connection4 in the same manner as the valves 56 and 51 control the flow through the equalizer connection of the previous embodi-v ments. The valve 51 is responsive to pressure in the vbleed connection and closes in response to rise in pressure' therein and the valve 56 is operated by the proportioning motor 69 and the controller 'l2 as in the previous embodiments.

Superheat control valve 331 comprises a tube 345 having a detent 346 at one end which se.

cures an' end plug 341 in position. A screw 348 extends through the end plug 341 and near its Y l inner end the screw 346 has a shoulder 349, and

between the shoulder 349 and the end plug 341- is a fiben washer or disk 350 to preventleakage of fluid from within the tube 345 around the screw 348. A lock nut 35| may be provided on the screw 348 external of-the tube 345 so that screw 348 may be locked in any adjusted posi tion. The inner end of the screw 348 is slotted4 356 or other suitable clamping means so that the tube 345 and the portion 305 of the outlet pipe are in intimate thermal engagement whereby'the bimetal element 352 is responsive to the temperature of superheated refrigerant in the outlet pipeof the evaporator.

The pilot valvt` mechanism 331 includes another tube 360. the end of which is telescoped within the tube 345 .and itsend being in abutting relationship with the disk 354. The opposite end of the tube 360 is closed by an end plug 136| having a bore 362 to vwhich the pipe 336 is connected, and a counter-bore 303.v Within the tube 360 is lanother helical bimetal element 364, the right end of which engages in a slot at the end of pin 353 and the left end of which is engaged in a slot in a screw-threaded-member 365 which engages ,the counterbore 363 in screwthreaded relationship. The member 365 carries a valve head 366 which engages with the bore 362. The member 365 has a longitudinal groove 361 so that refrigerant entering through the bore 362 can pass through the groove into the tube 360. 'I'here is another bore 368 in the end plug 36| to which is attached the pipe 330.

The valve head 366 is slightly scored so that at least a small amount of refrigerant can always pass through the pipe 336 and the bore 362 and groive 361 to the interior of tube 360. When the valves 56 and 51 are in wide open position, the interiorof the tube 360 is in communication with the evaporator by means of the pipes 338,v 333 and 340 and the said valves. Thus, the pressure within the tube 360 is substantially the sane as that within ther evaporator and the temperature within the tube 360 is the vaporization temperature corresponding to the pressure existing at the time within the evaporator. The temperature alecting the'bimetal element 364 therefore corresponds to the pressure within the evaporator and the bimetal element 364 therefore operates the valve head 366 responsively to the pressure within the evaporator. 'I'he bimetal elements 364 and 352 act in opposition, the bimetal ele`- ment 364 acting to move the valve member 366 towards its seat when the temperature aiecting that element rises and the bimetal element 352 acting to move the valve member 366 away from its seat when the temperature aifecting that element rises. When element 364 moves valve member 366towards its seat, the rate 'of vbleed from within the interior of cell 320 is reduced tending to cause the pressure therewithin to increase and move the valve member 326 towards its seat to restrict the ow of refrigerant to the evaporator. When the bimetal element 352 moves the valve member 366 away from its seat, the rate` of bleed from the 'interior of-,the cell 320 is increased causing the pressure within the cell to be reduced so that the expansion valve 30| -tendsv to open. Thus it can'readily be seen that the pilot valve mechanism 331 controls the expansion valve 30| in accordance with the degree of superheat existing at the outlet of the evaporator |1 inasmuch as the elements 364 and 352 control the expansion valve 30| in accordance with the pressure within the evaporator and the temperature of the superheat at the outlet, increasing evaporator pressures tending to close the expansion valve and increasing temperatures of refrigerant at the outlet of the evaporator tend-g ing to open the expansion valve. words,a constant difference is maintained between the temperature of saturated refrigerant in the evaporator and superheated" refrigerant at the outlet.

The degree of superheatto be maintained may be readily adjusted manually by adjusting the -screw 346 to adjust the bimetal elements and the position of the valve head 366.

In normal operation when the control valves 56 and 51 are Widebpen the pilot valve mechanism 331 controls the superheat at the, outlet of the evaporator. As in the previous embodiments however, the capacity ofthe evaporator may be controlled by the control valve 56. yAs the temthe valve 56 is moved.` As the pressure within the tube 360 is increased the temperature of the refrigerant therein, will correspondingly increase,

the vapor within the tube at all times being saturated of course. As the temperature affecting element '364 increases, 'valve member 366 is moved towards its. seat tending to restrict the rate of bleed from `within the cell 320. Thus the pressure within cell 320 will increase causing the valve 30| to move towards closed position. From the foregoing it will be seen that as valve 56 is moved towards closed position the temperature affecting element 364 is increased and the pilot valve mechanism 331 will maintain a higher degree of superheat at the outlet of the evaporator. In other Words, the valve 56 is effective to control the capacity of theevaporatr but the pilot valve mechanism 331 atall times is incontrol of the superheat at the outlet and maintains the degree is determined by the valve 56.

As in the previous embodiments, under certain circumstances there may be heavy cooling loads l and the pressure 4within the evaporator willbe relatively high tendingrto place a heavy load on the compressor motor. At these times it is de` sirable to reduce the capacity of the evaporator` by restricting the admission of refrigerant thereto. When the evaporator pressure rises to a predetermined value, the bellows 85 is expanded against the force exerted by spring v89 moving the control valve 51 towards closed position. This action of the control valve 51 will cause the pressure within tube 360 to be increased in the same manner as when the valve 56 moves towards closed position as described above.v Thus as the valve 51 closes in the sameV manner as described above when valve 56 closes the pressure within the cell 320 will build up causing the valve 39| .'such avalue as to completely close the expan to restrict the flow of refrigerant to the evaporator. If the pressure in the evaporator rises to a given 'relatively high value causing the valve 51 to completely close, the bleed from within the cell 320 is entirely cut off and the high pressure being metered to the interior of the cell 320 causes the pressure therewithin to build up to sion valve 30 l Thus it is to be s eenthat the control valve 51 serves to limit the evaporator pressure and to thus limit the capacity of the evaporator` andthe load which maybe placed upon the compressor motor. Normally, however, the valve 51 is in openposition andit does not interferewith the control ofthe'expansion ,valve by perature aiecting the controller 12 tends to fall, l

the pressure within the tube 360 will build up to a value higher`- thanthe pressure in the evaporator. Thepressurewith'in-1theltube 360 will be higher than the pressure'within the' evaporator depending upon how far towards closed position the superheat control valve 331' and the temperature responsive valve 56. A

From the foregoing, one skilled in the art will appreciate that I have provided avery convenient system wherein a small and inexpensive valve serves to limit the capacity of an evaporator so as to prevent the compressor motor from becoming overloaded. This small supplemental valve is normally inactive and-"does not interfere rwith the control of the 'system from the other control valves which arenormally in control.

In the system of Figure 3:1l'oat operated pilot valves might be-substituted for the valve 331 so as to control the refrigerant supply in accordance with the accumulation of refrigerant in the high or low side of the system. 'In all the embodiments, a proportioningcontroller responsive to evaporator pressure might be used in lieu of the pressure responsive valve, tl`1is controller be- In the form of the invention shown in Figure 1 it is`-within the purview of my invention to provide communication between the inlet of the evaporator and chamber 39 by means of a separate pipe connection. With such a pipe connection the relative effectiveness of the communica- .tion between chamber 39 and the inlet and the outlet of the evaporator might be varied by means of a three Way valve as in my prior application Serial No. 243,843 referred to above.

hTe embodiments of my invention which I have disclosed are representative of various forms which it may take. Many modifications and changes may be made in the invention and its scope is to be determined not in accordance with my disclosure but only by the claims appended hereto.

I claim as my invention:

1. In a refrigerating system, in combination, an evaporator of a type having a pressure drop between its inlet and outlet, an expansion valve of the superheat control type having a pressure responsive element, means connecting said element and a portion of said evaporator wherein the pressure is' lower than at the inlet so as to subject said element to said lower pressure, valve means in said connecting means, and an element responsive to evaporator pressure for maintaining said valve open for all normal evaporator pressures but closing said valve when said evaporator pressure reaches a value indicating that the cooling load is excessive so that the pressure responsive element of said expansion valve is less l subject to said lower pressure as said valve means closes off the connecting means.

2. In a refrigerating system, in combination, an evaporator of a type having a pressure drop between its-inlet and outlet, an expansion valve of the superheat control type having a pressure responsive element, means connecting said element and a portion of said evaporator wherein the pressure is lower than at the inlet so as to subject said element to said lower pressure, means providing relatively restricted communication 'between said element and a portion of said evaporator at relatively higher pressure, and valve means in said connecting means having an'element responsive4 to pressure within said connecting means for closing off said last means as the pressure therein increases so that the pressure responsive element of said expansion valve is less subject to said lower pressure as said valve means closes off the connecting means.4 i

3. In a refrigerating system, in combination, an evaporator of a type having a pressure drop between its inlet and outlet, a pressure operated expansion valve having a pressure responsive element, means connecting said element to a portion oi' said evaporator wherein the pressure is lower than at the inlet so as to expose said element to said lower pressure, said pressure urging said valve in closing direction, a valve in said connecting means, and means responsive to vaporator pressure for maintaining said valve open for all normal variations in evaporator pressure but closing oi said connecting means as the evaporator pressure increases above a value indicating an excessive cooling load so that as evaporator pressure increases above such value said element is exposed progressively less and less to said lower pressure, causing said expansion valve to move progressively in closing direction irrespective of temperature conditions.

4. In a refrigerating system,in combination, anl evaporator of a. type having a pressure drop between its inlet and outlet, a pressure operated expansion valve having a pressure responsive element, means connecting said element to a portion of said evaporator wherein the pressure is lower than at the inlet so as to expose said element to said lower pressure, said pressure 4urging said valve in closingI direction, a valve in said connecting means, means responsive substantially to evaporator pressure for maintaining Zsaid valve open for all normal variations in evaporator pressure but closing oi said connecting means as the evaporator pressure increases above a value indicating an'excessi've cooling load so that as .evaporator pressure increases above such value said element is exposed progressively less and less to said lower pressure causing said expansion valve to move progressively in closing direction irrespective of temperature conditions, and an additional temperature responsive valve in said connecting means for controlling said expansion valve.

5. In a refrigerating system, in combination,

between its inlety and outlet, a -pressure operated expansion yvalve having a pressure motor, means connecting said motor and a portion of said evaporator wherein the pressure is lower than at the inlet, so as to expose said motor to said lower pressure, said pressure tending to move said valve in closing direction, means providing restricted communication between said motor and the upstream side of the expansion Ivalve, a valve in l said connecting means responsive substantially to evaporator pressure for closing off said connecting means as evaporator pressure increases whereby pressure accumulates in said 4 motor tending to cause expansion valve to move proportionately in closing direction as evaporator pressure increases, and a valve in said connecting means of a superheat control type responsive to superheat at the outlet of the evaporator controlling said -connecting means to control said expansion valve in accordance with superheat. l

6. In a refrigerating system, in combination, an evaporator of a type having a pressure drop between its inlet and outlet, a pressure operated expansion valve having a pressure motor, means connecting said motor and a portion of said evaporator wherein the pressure is lower than at the inlet so as to expose said motor to said lower pressure, said pressure tending to move said valve in closing direction, means providing restricted communication between 'said motor andr the upstream side of the expansion valve, a valve in said connecting means responsive substantially to evaporator pressure for closing off l said connecting means as evaporator pressure increases to cause said expansion valve to move proportionately in closing direction as evaporator pressure increases, a valve in said connecting means of a superheat control type responsive 7. In a refrigeratingsystem, in combination,

refrigerant supply means, an evaporator and an expansion valve controlling the supply of refrigerant tothe evaporator, said expansion valve having pressure responsive operating means. r

means for conveying pressure from the upstream amasar side ofsaid valve to said operating means and means for bleeding pressure from said operating means to the downstream side of the valve, pilot valve means controlling the pressure applied to said pressure responsive operating means, and means responsive to evaporator pressure for maintaining said pilot valve means in a position to permit said expansion valve to open wide under all normal evaporator pressures, said evaporator responsive means being arranged to control the pressure on said pressure responsive operating means to cause closure of said expansion valve when said evaporator pressure increases to a value indicating an excessive load on said refrigerant supply means. i 8. In a refrigerating system, in combination, refrigerant supply means, an evaporator, and an expansion valve controlling the supply of refrigerant to the evaporator, said expansion valve having pressure responsive operating means, means for conveying pressure from the upstream side of said valve to said operating means and means for bleeding pressure from said operating means to the downstream side of the valve, pilot valve means controlling said bleeding means, said pilot*l valve means being responsive substantially to evaporator pressure and having means whereby flow through said bleeding means is permitted by said pilot valve means for all normal evaporator pressures but is cut olf at predetermined relatively high evporator pressures causing pressure to build up in said operating means, said relatively high evaporator pressures being indicative of an excessive load on said refrigerant supply means, and said operating means being arranged to close said expansion valve when the pressure builds up in said operating means. y 9. In a refrigerating system, in combination, refrigerant supply means, an evaporator, and an expansion valve controlling the supply of re frigerant to the evaporator, said expansion valve having pressure responsive operating means. means for conveying pressure from the upstream side of said valve to said operating means and means for bleeding pressure from said operating means to the downstream side of the valve, pilot valve mean's controlling the pressure applied to said pressure responsive operating means, said pilot valve means being responsive to evaporator pressure and being constructed and` arranged to so control the pressure applied to said operating means as to cause said expansion valve to close in response to relatively high predetermined evaporator pressures which indicate an excessive load being placed on the refrigerant supply means and to permit said expansionvalve to open for al1 normalevaporator pressures, and additional temperature responsive valve means controlling the pressure applied tosaid operating means for controlling said expansion valve.

10. In a refrigerating system, in combination, refrigerant supply means, an evaporator, and an expansion valve controlling the supply of refrigerant to the evaporator, said expansion valve having pressure responsive operating means, means for conveying pressure from the upstream sidev of said valve to said operatingmeans and means for bleeding'pressure from said operating means to the downstream side of the valve, pilot valve means controlling the pressure applied to said pressure responsive operating means, said pilot valve means being responsive to -evaporator pressure and being constructed and arranged to so control the pressure applied to said operating means as to cause said expansion valve to close in response to relatively high predetermined evaporator pressures to 'prevent excessive load being placed on the refrigerant supply means, and valve means responsive to the superheat at the outlet of the evaporator controlling the pressure applied to said operating means for normally controlling said expansion valve.

' 11. In a refrigerating system, in combination, refrigerant supply means, an evaporator, a main valve in control of the flow of refrigerant from said supply means to said evaporator for maintaining a constant superheat at the outlet of said evaporator, a pressure motor in control of said main valve, a pilot valve control of the pressure to which said pressure motor is subjected, means responsive to the load on the refrigerating system in control of said pilot valve, and a second pilot valve in control of the pressure to which said pressure motor is subjected, said'second pilot valve being responsive to the pressure in the evaporator and being operative only upon a pressure in the evaporator indicative of an excessive cooling load on said refrigerant supply means to control the lpressure of said pressure motor in a manner to increase the superheat maintained by said main valve.

12. In apparatus of the character described. in combination, means forming a refrigerating system including a source of refrigerant and an evaporator, valve means comprising an expansion valve adapted to maintain a constant superheat at the outlet of the evaporator for all normal evaporator pressures by controlling theadmission of refrigerant thereto, and means responsive to a relatively high evaporator pressure indicative of an excessive cooling load operativelyconnected with said expansion valve for increasing the superheat maintained thereby.

ALWIN B. NEWTON.

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