US2214236A - Dual pressure control for refrigeration systems - Google Patents

Description

Sept. 10, 1940. cs. E. SELDON 2,214,236

DUAL PRESSURE CONTROL FOR REFRIGERATION SYSTEMS Filed Dec. 9, 19:57

INVENTOR macaw 10,1940 l 2,214,236

UNITED STATES PATENT OFFICE DUAL PRESSURE CONTROL FOR REFRIG- ERATION SYSTEMS George E. S'eldon, Detroit, Mich. Application December 9, 1937, Serial No. 178,867 20mm. (01.23642) This inventi r lat t dual pressure exheated condition of the refrigerant in the suction pansion valves" for controlling the flow of reline at all times, regardless of the pressures in frigerant to an evaporator or several evaporators the system. The pressure of the refrigerant at or each of the several sections of one evaporator the valve is applied to one side of a diaphragm of a compression type of refrigeration system. or bellows and a pressure exerted in response to 5 i There is-at present a class of valves for contemperature conditions in the suction line is aptrolling the flow of refrigerant to evaporators plied to the o h Side the ph m- A. that is known as thermostatic expansion valves". spring or weight is connected to the diaphragm in Thermostatic expansion valves are designed tosuch manner that a constant forceis exerted in regulate the flow ofrefrigerant through refrigopposition to the pressure that is responsive to 10 eration systems in accordance with temperature the temp u e conditions in the Suction 11116 conditions in predetermined parts of the system. of the compressor. This force, therefore, is added The predetermined parts of the system usually to the pressure exerted by the refrigerant at the are the expansion valve and the suction line of valve. The pressure that is responsive to the h pressor. The valves are so designed that temperature conditions of the suction line, therevthe temperature of the refrigerant in the suction fore, must be higher than the pressure of the reline of the compressor must be a predetermined frigerant at the valve. To secure ahigher presnumber of degrees higher than the temperature sure at the suction-line, the suction line must be of the refrigerant at the valve, before the valve hotter than the valve. Since the valve will be will open. Since the refrigerant at the valve is at the boiling point. the suction line will be hot- 20 at 'the boiling point, the requirement of 'additer and willvaporize all of the refrigerant passtional degrees of temperature in the suction line ing therethrough. The operation of the valve. is of the compressor guarantees that the refrigersuch that until the temperature of the suction ant in the suction line will be superheated and, line is a predetermined number of degrees higher therefore, completelyin the vapor phase. Bethan the temperature of the refrigerant at the 25 cause the refrigerant in the suction line of .the valve, the valve will be closed. When the temcompressor is completely in the vapor phase, it perature of the suction line is high enough to is impossible for liquid refrigerant to flow into superheat the refrigerant at the pressure and in the suction line of the compressor. This avoids the system, the valve opens. The valve is demechanical breakdowns that follow the presence signed to stay open as long as the tempe tu 80 Y of liquid refrigerant in the suction line of the differential between the bulb and the valve equals cempressorv or exceeds a predetermined value, and is designed The pressure of the refrigerant in a refrigerato close when the temperature differential fails tion system is constantly changing as the amount to equal the predetermined value.

\ 5 of heat in the liquid tobe cooled changes. To Various temperature-responsive media have adequately. protect the refrigeration system from been used in the bulb thatis situated in heatthe flow of liquid refrigerant into the suction conducting relation with the suction line ofthe line of the compressor, it is necessary that the compressor. ihe media which has been found to refrigerant in the suction line be superheated. be most satisfactory ls'a'media in both the liq d 4 ns y changing Pressure in h y m r ture range of the valve, that possesses the tem- Sults in ednstantly, changing bo l p int for perature-pressurecharacteristics of the refri h r r er t a n tantly changin temrant. Such a media will permit the valve to stay perature level required to insure a superheated open as long as the predetermined temperaturecondition of the refrigerant in the suction line of differential exists between the refrigerant at the the p 'e It therefore, impractical to valve and the refrigerant in the suction line of set a fixed temperature level in the suction lineto the compressor. This permits the use of full assure a superheated condition of the refrigerant evaporator capacity under all evaporator condittherein. Adequate protection for the compressor tions. The use of such amedia makes possible ardless of the pr in the y m Th and the vapor phase during the normal tempera- 40 can be afforded byv a dual pressure expansion the use of a limited charge in the b- A 50 valve which maintains a temperature level in ited charge is partially in the liquid and partially the suction line of the compressor that is a prein the vapor phase durin he Hormel p -f I determined and constant number of degrees ture range of the valve but the mediav is com-,

r above the temperature level of the refrigerant at pletely in the vapor phase when the temperature the valve. Such a valve will maintain a superinthe suctipn line rises above a predetermined 5 temperature after a predetermined temperature is reached. This permits the valve to open in response to increases of temperature in the suction line, until the temperature reaches a predetermined level whereupon the valve will close because the media in the vapor phase will be unable to keep pace with the rising pressure of the refrigerant at the valve. The pressures exerted by the refrigerant in the suction line at temperatures above the predetermined level are so much greater than the normal operating pressure, that the motor which operates the compressor would be overloaded. Such; overloading can-seriously injure the motor and greatly shorten its life. The

use of a limited charge inthe 'bulb prevents the opening of the valve when the temperature and pressure of the refrigerant in the evaporator rise above a predetermined level.

Dual pressure expansion valves that are now 1 being used are divided into two classes. The first class is known as the insulated fluid type.- This type of valve has a bulb situated in heat-conducting relation with-a portion of the suction line of the compressor, an expansible bellows within a valve casing, operating in response to pressures exerted by the bulb; thattends to open the valve, and an expansible bellows, responsive to the pressure of the refrigerant in the evaporator, that tends to close the valve. There are twotempera ture-responsive bellows within the casing surrounding the valve that exert a force on the valve, but'the two bellows must be insulated from each other. In such valves, definite temperature relationships must be maintained between the bulb and the two bellows to insure continued operation of the valve.

The other type of dual pressure expansion valve is known as the intimate fluid type. In

this type pressure corresponding to the heat of the refrigerant in the suction line of the compressor is applied to one side of apressure-responsive diaphragm and tends toopen the valve, while the pressure exe ted by the refrigerant at the valve is exerted on the other side of the pressure-responsive diaphragm and tends to close the valve. This type of valve has a simpler construction than that used in the insulated type valve but must still maintain definite temperathe hottest liquid be in the ii'ulb. In the case of the insulated fluid type expansion valve, the only liquid, in the part of the control which tends to open the valve, is situated in the bulb. The pressuremesponsive bellows located in the valve casing must, therefore, be warmer than the bulb to prevent accumulation of liquid in the bellows. The accumulation of liquid in the bellows would serve to shiitthe control of the valve from the bulb to the valve casing, and the temperature of the latter would control. This obviously would be undesirable and, therefore, it is necessary that the bulb be cooler than the bellows. Such a requirement prevents the immersion of the valve of the valve casing in the liquid to be cooled and makes it advisable to locate the bellows outside of the cooling compartment. Such a requirement seriously limits theversatility and utility of this type of valve. In the case of the intimate fluid type expansion valves. the design is such that the temperature of themedia on each side of the pressure-responsive diaphragm is approximately the same, exclusive of outside influences. Since the temperature of the refrigerant in the valve is lower than the temperature in the suction line of the compressor, the bulb is usually warmer than the media in contact with the pressure-responsive diaphragm. Since-the media condenses in the cooler portions of the control system, media will be folmd in the liquid phase next to the pressure-responsive diaphragm. In order for the control to be in the bulb where it should be, the liquid inthe bulb must be hotter than the liquid next to the pressure-responsive diaphragm.

- For this reason, the valve casing which contains thepressure-responsive diaphragm cannot be immersed in very hot liquids, because the liquid in the casingwould be hotter than the liquid in the bulb, and the control would shift from the bulb to the valve casing. This condition is disadvantageous and seriously limits the utility of this type of valve.

The shifting of controlto which all dual pressure valves now in use are subject is undesirable and makes ,the-valves ineflective as a regulator of the flow of refrigerant in accordance with the superheat in the refrigerant in the suction line.

The applicant avoids this condition by absolutely confining the media in ahousing in the bulb and transmitting the pressure exerted by the media to the pressure-responsive diaphragm in the valve casing by substantially heat-insensitive means. Such an arrangement permanently restricts the control to the bulb, and insures the proper operation of the valve in accordance with the s perheat in the refrigerant in the suctionvalve does not touch the evaporator, since the capillary tube is filled with media. Ifthe tube were cooler than the valve or bulb, the media would condense there and might shift the control from the bulb. Bucli a condition has been knownto exist in practice, and it endangers the safety of the refrigeration equipment. The applicant avoids such a problem by transmitting pressures generated in the bulb by a substantially heatinsensitive liquid.

It is sometimes desirable to use one control for a number of evaporators. With every other. valve known in the prior art, such an arrangement would necessitate the re-engineering of the bulb and valve. The device of the applicant 'alone can use the same bulb for one or more valve casings.

It is an object then of this invention ,to provide a refrigerant control valve responsive to the superheat of the refrigerant wherein the temperature of the valve inno wise modifies its action or limits its adaption to a restricted field.

It is another object to provide a valve adapted '2,214,ase 3 to remain closed above a fixed evaporator.pressure yet requiring no insulation of the power element from the rest of the valve thereby reducing its cost. v 5 It is a further object to produce a valve and a temperature responsive bulb independent of each other for purposes of manufacture, shipping and field assembly, but complementary in actual use. a e 1 It is a further object to provide a thermostatic bulb and closed pressure control system whereby one thermostatic bulb can control more than one .valve... It is a further object to provide a valve or 15 cluster of valves controlled by a closed hydraulic system having a hydraulic brake in thesystem to dampenthe fluctuations of the valves. 7

Other objects will be apparent to one versed in the art from the following description and the 20 accompanying drawing. f

The drawing shows a compression type refrig- 'eration system as applied to a cooling evaporator of two sections one of which is below the other and in a tank 39 containing water. The numeral I denotes a compressor, 2 is a condenser,

3 a reservoir, 4 a liquid refrigerant line to two dual pressure expansion valves 5 and 6 discharging into two sections] and 8 of the evaporator which is connected to the return mani- 30 fold 9 leading tothe compressor. Clamp. I0

holds 'the master thermostatic bulb in intimate contact with the return manifold allowing the free exchange of heat between them.

The master thermostatic bulb II contains two 35 chambers an inner I2 and an outer I3 separated by a pressure responsive surface which in this case is bellows I4. A casing I5 forms the outside wall and has outlet fitting I! which is brazed to connecting pipe I8. Orifice I9 forms the con- 40 nection between this chamber I3 and the tube I8. The inner chamber is charged with the volatile thermostatic fluid through tube I6 of the chamber sealing header 2! and is surrounded by the inert hydraulic liquid filling chamber I3.

5 and passing out through the orifice I9 into the closed and sealed hydraulic control system.

The orifice acts as a hydraulic brake checking the tendencies of the hydraulic liquid to respond to fluctuations set up by the needle in the valve 50 seat. The inner chamber is charged with the volatile thermostatic fluid which is usually the same as the refrigerant used in the refrigeration system and preferably charged at a pressure lower than that corresponding to the charg- .55 ing temperature, thereby establishing a pressure below which the charge is partly in vapor phase and partly in liquid phaseeand above which it is entirely in vapor phase and the pressure no longer increases according'to the characteristic 60 vapor pressure temperature relation of the hind but rather the laws of Boyleand Gay-Lussac.

Hence within the temperature range of the valve the charge can be so adjusted in amount that a definite predetermined pressure is the maximum 5 thecharge can exert and consequently the maximum that the hydraulic liquid can .be subjected to and in turn can exert.

The closed hydraulic control system comprises chamber is, tube I8, header 2 tubes 22 and 2a 7 and the hydraulic liquid control chamber ,of

the valves as shown in section at 25. Header 2| distributes the hydraulic control liquid to the valve or valves of the system, it also serves as a disconnecting and filling point. The tubes I6. 75 22 and 23 are brought to this header and there without disturbing the operation of-the other valve. The number of valves that can be con- .trolled by one master thermostatic bulb is governed by the relative size of the bellows I4 and 10 the area and movement of diaphragm 29. The closed systemis charged with liquid through opening in the header 2| normally closed by plug 24.

Filling the closed hydraulic control system with the liquid is an operation that can readily be performed in the field though usually the' con-' nections will be -made at the plant making the assemblies. However if necessary say to lengthen the tube connecting the-bulb and the valve in the field such lengthening can be accomplished by simply opening the control system brazing in the required length of tubing and refilling the system with liquid and replacing plug 24. Heretofore such a lengthening of a tube in the field was most inexpedient if not impossible,

especially with vapor charged valves using the maximum operating pressure charge. Not only is it now possible to lengthen the tube in the field but also to add additional valves or thread the connecting tube through a hole too small for the bulb in a fitting or evaporator wall and connect the bulb on the other side.

Since valves 5 and 6 are of identical construction it will suifice to describe one only, consider 6. The control liquid enters the dual pressure valve through sweat-connection which isthe means for connecting the valve to the closed con-- trol system; and the tube 22 is solder sweated or brazed tothe valve at this point. There is also orifice 21 which can be a hole of very fine bore say .016 inch diameter. The orifice is a means for dampening the fluctuations and-vibrations sometimes set upby the throttling action of needle valve on the orifice seat. The hydraulic liquid control chamber 25 of the valve is made of the cover 28 and the pressure responsive surfacethe diaphragm 23. On the other side of the diaphragm is the chamber 30 which is ported to connect with the outlet and tube 3I of the evaporator section 6. Housing 32 forms the other side of chamber 30. Orifice 33 opens into this chamber and has needle valve 34 placed therein and adapted to close it and regulate the size of the opening available tothe Iii;v

liquid refrigerant entering the valve through refrigerant line 4; The valve 34 can be moved oflits seat by the action of the diaphragm due to pressure of'the hydraulic control liquid, theaction of the valve is also modified by thespring 0 35 with its adjustment screw 36 and this spring 35 is the means-used to apply an 'exteriorload to the pressure sensitive surface.- Gasket 31 and screw 38 close the valve. In action during the refrigeration cycle, after the motor has started .65 the compressor begins to draw the refrigerant vapor out'of the evaporator thus lowering the ,terior spring load the valve opens and allows imately that of the evaporator and the valve can not open due to the fluid and the refrigerant acting on the same effective area of the pressure responsive surface. The valve can only open when the pressure in chamber 25 is greater than the combined pressure of chamber ill and the spring load. But the pressures in 25 and 30 would be equal for equal temperatures so it is apparent that the spring 35 is useful to regulate the difference of temperature between the two points considered, in'other words the load of the spring -35 controls the superheat of the vapor. It will also be seen that each dual pressure valve in the refrigeration system can have its own superheat setting without interference fromthe other valves of the system and each valve can be adjusted to compensate for variations of load and refrigerant head on it. It is also feasible to have several evaporator-s at different points similarly controlled, i. e. a valve on each evaporator and a master bulb at the outlet of one' of them. .It will beseen for such operation the bulb containing the volatile fluid is in intimate contact with an outlet pipe leading from the evaporator which pipe with its rapidly moving refrigerant is a body having more than ample thermal capacity to control the temperature of the bulb and consequently its vaporization pressure. This vaporization pressure is converted at the bulb to hydraulic pressure at practically the same value which in turn can control the refrigerant flow to several evaporators through dual pressure valves. These evaporators need not be in the same refrigeration system, it is only necessary that the other system operate at a temperature so related to the master system in which the bulbJs' located that the temperature difference comes within the range of the spring adjustment available, and the refrigerant used should be the same or have substantially similar characteristics and the evaporators should have approximately the .same elevation.

What I claim and desire to secure by Letters Patent 'of the United States is: y

1. A dual pressure control for a refrigeration system comprising a valve casing having an inlet for refrigerant, an outlet for refrigerant, a

valve adapted to regulate the flow of refrigerant through said valve casing, a pressure-responsive diaphragm to operate the valve, means biasing the valve to closed position, means to permit refrigerant at evaporator pressure to contact one" side of the diaphragm and exert pressure thereon tending to close the valve; a'feeler bulbcasing having an expansible bellows positioned therein and attached thereto, said feeler bulb casing containing a temperature-responsive media that partially in the liquid and partially in the vapor phase throughout the normal temperature range of the feeler bulb casing and completely in the vapor phase whenever the temperature of the feeler bulb casing rises above a predetermined level, said temperature-responsive media being adapted to exert pressure on the expansible bellows in response to the temperature in a predetermined portion of the refrigeration system,

- and a hydraulic system comprising a fluid tight chamber in the valve casing having a portion of one of its walls formed by the pressure-responsive surface, .tubing connecting'said fluid tight chamber and the feeler bulb casing, and a substantially heat-insensitive liquid completely filling the fluid tight chamber in the valve casing the tubing connecting theifluid tight chamber and the feeler bulb casing and that part of the feeler bulb casing not occupied by temperatureresponsive media, said hydraulic system being adapted to transmit pressure from the bellows,

, phragm, an inlet for refrigerant, an outlet for refrigerant, a valve adapted to regulate the flow of refrigerant through said valve casing said pressure-responsive diaphragm being adapted to operate the valve, means biasing the valve to closed position, means to permit refrigerant at evaporator pressure to enter the refrigerant chamber and contact the pressure-responsive diaphragm and eiert pressure thereon tending to close the valve; a feelerbulb casing having an expansible bellows positioned therein and attached to one end thereof, said feeler bulb casing containing a temperature-responsive media that is adapted to exert pressure on the expansible bellows in response to the temperature in a predetermined portion of the refrigeration system, said temperature-responsive media being partially in the liquid and partialy in the vapor phase throughout the normal temperature range of the feeler'bulb casing and completely in the vapor phase whenever the temperature of the feeler bulb casing rises above a predetermined level whereby the pressures exerted by said temperature-responsive media increase greatly for small increases in temperature during the 'normal temperature range of thefeeler bulb casing and increase slightly for large increases in temperature whenever the temperature of the feeler bulb casing rises above a predetermined level,

ing'said hydraulic chamber, the tubing connecting 'the feeler bulb casing with the hydraulic chamber and that part of th feeler bulb casing not occupied by temperature-responsive media,-

said lwdraulic system being adapted totransmit pressure from the bellows in the feeler bulb casing to the other side of the pressure-responsive diaphragm in the valve casing whereby the temperature conditions at the valve casing cannot directly affect the temperature responsive media, said pressure transmitted by the hydraulic system being adapted to bias the valve to open position. 1

GEORGE E. SELDON.

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