US2977039A - Control circuit - Google Patents

Description

March 1961 w. E. GREEN EI'AL 2,977,039

CONTROL CIRCUIT Filed July 10, 1958 2 Sheets-Sheet 1 FIG. 1.

F E J. 6 l7 C 40 INVENTORS.

ERNEST H. STARK WILLARD E. GREEN L WW ATTORNEY 2 Sheets$heet 2 30 A Y U \RKFM.

CONTROL CIRCUIT W. E. GREEN EI'AL March 28, 1961 Filed July 10, 1958 INVENTORSZ WILLARD E. GREEN BY ERNEST H. STARK ZZZ/ W ATTORNEY gg k V un sd W8 Pa ent .0

2,977,039 CONTROL CIRCUIT Willard E. Green, Olean, N.Y., and Ernest H. Stark, Michigan City, Ind., assignors to Joy Manufacturing Company, Pittsburgh, Pa., a corporation of Pennsyl- Vania Filed July 10, 1958, Ser. No. 747,784 13 Claims. (Cl. 230-2) This invention relates to a control circuit and more particularly to a fiuid control circuit for isolating a rotary compressor from its receiver.

In the art of rotary compressors it is common practice to discharge the high pressure medium directly to a receiver from which the high pressure medium is drawn as needed. Where there is a steady demand for the compressed medium the compressor continues to discharge the high pressure medium to the receiver. Underconditions of small or no demand for the compressed medium no compressed-medium is drawn from the receiver and the high pressure ofthe receiver is exerted against the high pressure stage of the compressor. As can readily be appreciated more energy is required to drive the compressor against the receiver pressure than is required to drive the compressor against a pressure substantially lower than the receiver pressure. Heretofore with rotary compressors driven by a variable speed prime mover, suchas a gasoline or diesel engine, it is possible to reduce the energy consumption of the prime mover by merely reducing its speed in some suitable manner such as that shown in the copencling application of Willard Green, entitled Control Device, Serial No. 699,838, filed November 29 1957, which application hasbeen assigned to the same assignee as-the assignee of this invention. In other rotary compressors in which the rotating elements are driven by a constant speed prime mover, such as an electric motor, no means heretofore have been' provided for reducing the energy requirements of the compressor during its unloaded condition. As can readily be appreciated such isolation of the receiver must be discontinued upon increased demand of the compressed medium and from a practical commercial standpoint such isolation and non-isolation must occur automatically to insure efiicient operation of the compressor and a sufficient supply of the compressed medium.

Accordingly one object of this invention is to provide a new and improved control circuit for a rotary compressor for isolating the compressor from its receiver when there is little or no demand for compressed medium and for discontinuing such isolation upon increased demand for the compressed medium.

Another object of this invention is to provide a new and improved control circuit for a rotary compressor for isolating the compressor from its receiver which employs the changes in pressure-in an intermediate receiver of the compressor to obtain such-isolation.

'A specific object of this invention is to provide a new and improved control circuit for a rotary compressor forisolating the compressor from its receiver which obtains, such isolation in response to positive and negative 1,

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pressures existing in an intermediate receiver of the compressor. V These and other objects of this invention will become more apparent upon consideration of the following detailed description of a preferred embodiment thereof, when taken in conjunction with the following drawings, in which: 1

Fig. 1 is a cross section view including the inlet and discharge valves therefor of a typical rotary compressor which a circuit constructed in accordance with the principles of this'invention is adapted to control, and Fig. 2 is a diagrammatic representation of a rotary compressor, receiver, and auxiliary equipment connected together by a control circuit constructed in accordance with the principles of this invention.

In the description of this invention air has been employed as the medium'compressed by the compressor; however, it is to be realized that such use of air is for convenience only and that the principles of this invention are equally applicable to all types of compressor fluids. Referring .to Fig. 1 of the drawings it will be noted that a rotary compressor 1 of a construction which isadapted to be controlled by a control circuit of this invention comprises a suitable formed housing 2 having a vane supporting 'first stage rotor 4 which initially com' presses air admitted through an open inlet valve 6 from atmospheric pressure to an intermediate pressure. Such initially compressed air is discharged from the first stage rotor 4 through an opening 8 in the housing 2 through an intermediate receiver 10 formed integrally by the housing 2. Thereafter the initially compressed air is admitted through an'opening 11 in the housing 2 into a vane supporting second stage rotor 12 wherein it is further compressed to a desired final, high pressure. The

high pressure air is then discharged from the second stage is connected to a receiver 20. Inasmuch as the structure of such a rotary compressor 1, inlet and outlet valves, and receivers are well known in the art and do not constitute a part of this invention further descriptionthereof is not believed to be warranted.

As is customary the inlet valve 6 is provided with a valve head 5 which is movable into a closed position, as shown, so that no air can be admitted to the first stage rotor 4. Similarly the discharge valve is provided with a valve head 17, shown open, which is biased at all times by means of a suitable spring 22 towards its closed position. Under normal or loaded operating conditions, the second stage rotor 12 discharges high pressure air against the valve head 17 to overcome the bias of the spring 22 to open and hold the discharge valve 16 in its open position.

The control circuit of this invention depends upon the following operating characteristic of a constant speed rotary compressor. When the inlet valve 6 is closed the rotors 4 and 12 continue to rotate at a constant speed and, since no air is supplied to the first stage rotor 4, the rotation of the rotor 4 createsa vacuum in the space between the closed inlet valve 6 and the inlet of the rotor 4 which vacuum passes progressively through the compressor as the continually rotating second stage rotor 12 causes the intermedia eteceiyer 10in turn to. be evacuated-which is sensed by line D in valve 100. When the receiver 20 remains connected to the discharge connection 15 the rotor 12 must continue to operate against the receiver pressure on its discharge side while a vacuum exists on its inlet side. The following pressure conditions of a rotary compressor under normal operating conditions have been setfor the purpose of illustration only. The first stage rotor 4 compresses air from atmospheric pressure to an intermediate pressure of 30 lbs. per square inch gauge in the intermediate receiver 10 and the second stage rotor 14 compresses the intermediate receiver air from 30 lbs. per square inch gauge to 100 lbs. per square; inch gauge. In view of the fact that the air discharged from the rotor 12 holds the discharge valve 16 open the receiver 20 is normally .at a pressure of 100 lbs. per square inch gauge. With the :inlet valve 6 closed the same compressor has a vacuum of l to l2 .lbs. per square inch gauge in .the intermediate receiver and the second stage rotor '12 operates :between a vacuum of l0 lbs. per square :inch gauge to l2 lbs. per square inch gauge on its inlet side to 100 lbs. per square inch gauge on its discharge side. In addition it should be borne in mind that in compressors of this type oil is normally injected into the air flowing through the compressor to provide for lubrication of and a sealing medium on the vanes of the rotors 4 and 12 and also to absorb the heat of the compression. Accordingly, such injected oil is discharged from the second stage rotor 12 to the receiver 20.

Referring to Fig. 2 it will be noted that the rotary compr'essor 1 shown in and described with relation to Fig. 1 has been shown diagrammatically therein. As is customary with the receiver 20, the inlet line 18 extends in wardly thereof to cause the majority of the oil discharged therein to collect at the bottom of the receiver 20.. Although not shown it is to be realized that even the most eflicient oil separating means does not remove all oil from the line 18 so that some high pressure air having oil entrained therein is also contained in the receiver 20 above the oil in the bottom of the receiver 20. In order to limit the amount of oil used in the compressor 1 a suitable oil flow line B is connected between the oil collecting portion or sump of the receiver 20 and to a novel control valve 100 the structure of which is more fully shown, described and claimed in Serial No. 747,725, filed July 10, 1958, entitled Control Device by Ernest H. Stark which application has been assigned to the same assignee as this invention. As will become apparent upon reviewing the above identified copending application the letterdesignation of the various fluid transmission lines connected to the control valve 100 in this application have been given the same letter designation as the fluid transmission lines in the above identified copending application so that ready comparison may be made there- 7 between. The valve 100 is provided with an exit line A which is connected to the line B under normal operating conditions of the compressor.

The line A is connected to a thermal bypass valve 24 which has an exit line 26 connected thereto with the remote end of the line 26 being connected to a suitable oil pump 28. The oil pump 28 is provided for the purpose of both lubricating the compressor and injecting oil into the air flowing therethrough. In addition the oil pump 28 may be employed to lubricate a driving means 7 which is connected to the rotary compressor to cause rotation thereof as is well known in the art. has much as the internal structure of the compressor and the drive means 7 for obtaining such lubrication and injection of oil is well known'in the art the particular description thereof is not believed to be necessary. It will be noted, however, that the oil pump 28 is provided with a suitable discharge line 31 connected to the compressor 1.

The structure of the bypass valve 24 is well known in theart and does not constitute a part of this invention.

As is well known when the injected oil is cold, as during the initial starting of the compressor 1, oil flows from line A to line 26, so as to be immediately circulated through the valve 24'. After operation of the compressor 1 the oil collected in the receiver 20 which has been heated and the bypass valve, by means of a suitable thermal device actuated by the flow of heated oil therearound, disconnects the low resistance line A from the line 26. When the line A and the line 26 are so disconnected, the oil from the line A flows through a suitable fluid transmitting line 30 having a suitable filter 32 and a radiator 34 therein as are well known in the art to a portion of the bypass valve 24 to permit flow therethrough to the line 26. With such .a thermally controlled alternate path for the heated oil the heat of the oil may readily' be removed so as to insure its ability to absorb the heat ofthe compression in a manner as well known in the art.

The oil entrained in the oil-air mixture in the receiver 20 is also employed to lubricate. portions of {the compressor sequentially located after the intermediate receiver 10. Accordingly the air-oil mixture portion of the receiver 20 is connected by a suitable line H through a valve 52 to a line G the other end of which is connected to the intermediate receiver it). Such connections and lines as the other connections and lines heretofore and hereinafter described may be made in any suitable manner as is well known in the art. The valve 10!) connects the line H to the line G when the compressor is running loaded as is shown in Figure 3 and more fully described in the latter identified copeudiu'g application. As indicated the compressor is isolated from the receiver 26 in response to pressure diflerences occurring in the interrncdiate receiver 10. Accordingly the intermediate receiver 10 is; connected to a chamber 130 in the valve by means of a suitable line D so that when the compressor 1 is operated to discharge compressed air the line B is connected to the line -A and line H is connected to the line G as is clearly shown by Fig. 3. Thus reciprocable piston 122 mounted in bore 106 of control valve 100 is biased rightwardly communicating line B with line A as shown in Fig. 3.

When the inlet valve 6 of the compressor is closed and a vacuum created in the intermediate receiver '10 such vacuum is transmitted through a line Dto the chamber of the valve 100 to thereby sense the fall in pressure and thereby cause operation of the valve "100 to an unloaded position so that the discharge lines B and H from the receiver 20 are closed. As shown in phantom lines in Fig. 3, the piston 122 will move leftward since a vacuum is created in chamber through line D whereas the right side of piston 122 and chamber 130 is connected to atmosphere via conduit 136 to thereby force the piston 122 in the direction of the vacuum. In order to obtain complete isolation of the receiver from the compressor it is also necessary to close the discharge valve 16 so that the pressure from the receiver 20 cannot be exerted against the second stage rotor 12. Such complete isolation of the receiver 20 is obtained by having the valve 100 when moved to an unloaded position as shown in phantom lines in Fig. 3 actuate an auxiliary valve 54 whereby a control line F is connected to a vent line B. This is accomplished by piston 122-striking a plunger upon leftward movement of the piston 170 wherein the plunger 170 unseats a spring loaded ball valve 16% thereby communicating control line F to vent line B. The operation of an auxiliary valve 50 and 52 of the valve 100 are more fully shown, described and claimed in the latter identified copending application. As shown in Fig. l the line F is connected between the discharge connection 15 and the auxiliary valve 50 and the line E is connected between another portion of the auxiliary valve 50 and passageway 36 (Fig. 1') extending through the discharge valve 16. The end of the passageway 36 remote from the line Eis connected to "a suitable line 6% eta-rag a It will be realized that when the valve 100 is moved from its normal loaded position when the compressoris discharging high pressure air to the receiver 20 to its alternative unloaded position shown in phantom lines in Fig. 3 when the compressor is disconnectedfrom the receiver 20, the high discharge pressure of the second stage rotor 12 exists in the discharge connection 15 which high pressure is transmitted by thelines F and ,E to the passageway 36. Thereafter. the high pressure air in passageway 36 is ventedslowly to atmosphere by means of the line 40 through the restrictive fitting 38. As is well known in the art,;'the, restrictive fitting in the end of the line 40 remote from the valve-16 ,does'not permit the pressure in the line 40a; collapse to atmosphere but bleeds the pressure in line 40' slowly' to atmosphere. Accordinglyyduring the time increment that line 40. is beingbled to atmosphere the oil pressurewhich exists in the discharge connection 15 also exists inthe passageway 36. In view ofthe fact that the flow through the line 40 normally comprises a mixture of oil and air'such oil-air mixture is bled into the housing of the dr'ive means 7 which is provided with a breather, as 'is well known in the art, to permit the pressure withinthe housing to escape to atmosphere. Such a structure permits the oil from the line 40 to collect in the bottom of the housing for the drive means 7 where it can be removed therefrom by means of a sump line 29 connected to the pump 28.

As shown in Fig. 1 such high pressure in the passageway 36 is directed against a plunger portion 17 of'the discharge valve which force in conjunction with the bias of the spring 22 moves the discharge valve 16 to a closed position in a manner as is well 'knowninthe art. As the discharge valve 16 is normally held openby air from the receiver is exerted against downstream side of the discharge valve 16 to hold the discharge valve in its closed position. Since the receiver 20 is now disconnected from the discharge connection 15 the discharge lines F and E, passageway 36, and line 40 from the discharge connection 15 slowly bleed the pressure from the :discharge' connection 15 to atmosphere which low pressure condition will prevail therein as long as the discharge valve' 16 remains closed.

It will be'realized, however, that with the rotors 4 and 12 constantly rotating it is necessary to provide some means for discharging the oil injected into the compressor. Accordingly it will be noted that an oil flow line C is connected to the discharge connection 15 and .to the fvalve 100 so that when the valve 100 moves to close the lines B and H,'the line C is connected to line A. Since lthelineC is so connected to the line A the oil may circulate through the same circuitry as heretofore described with relation to the oil from the line B. It will "be realized that since the pressure within the discharge connection 15 is dropped due to the vent line 40, when 'the discharge valve 16 is closed, the pressure in the line .C' and the line A will drop in accordance with'the pressure in the discharge connection 15. By referring to the latter identified copending application, it will be realized that such pressure drop in the valve'100 is employed to .locle the discharge valve 100 in its unloaded position.

I Should the demand for air from the receiver 20 increase the inlet valve 6 is'opened to permit air to flow through the compressor. Such air flow through the compressor causes the vacuum in the intermediate receiver -10 to be destroyed whereby the intermediate pressure in the intermediate receiver 10 is again created. Such :pressure is transmitted through the line D to the valve I;100'. which is of a structure to cause the valve 100 to zmove to its normal pperating position since the pressure created in line D will force the'piston' 122 rightward to- .wardits loaded position shown in full lines in Fig. 3

-wbereat the line F i di conne ed o t e n m grai e 5 3 F ui y line .C is concurrently, disconnected from line A.. Coricurrently, the line B is again connected to line A and line H is again connected to line G.

Thus it will be noted that this invention has provided an automatic means for isolating the receiver from the compressor when no demand for air from the receiver '20 occurs while also automatically returning the pressure to the receiver 20 when the demand for air from the receiver increases; Having described a preferred embodiment of this invention in accordance with the patent statutes, it is to be realized that modifications thereof may be made without departing from the broad spirit and scope of the invention. Accordingly it is respectfully requested that this invention be interpreted as broadly as possible and be limited only by the prior art.

Whatwe claim is: 3

1. A' control circuit for isolating a compressor having 'a discharge line with a high pressure medium flowing therethrough, a control means, a control line connecting How therethrough upon closure' thereof the pressure said control'means and said discharge line, a vent line operatively connected to said control line by said control means wherein said vent line has a means at a portion thereof'remote from said control means to slowly vent the pressure therein to a lower pressure, said vent line having means intermediate said control means and said portion thereof connected to said discharge linefor closing said discharge line in responseto flow of a pressurized medium therethrough at a pressure above said lower pressure while flow through said control line continues, and said control means connecting said control line to said vent vline when said means intermediate said control means and said portion thereof is actuated to close said discharge line. i

2. A control circuit for isolating a compressor having an inlet and outlet with said outlet connected to a discharge linewith a high pressure medium flowing therethrough,' a control valve operatively connected to said discharge line, a control line connecting said control valve to said discharge'line, a vent line operatively connected to said control line by said control valve wherein said vent line has discharge means at a portion thereof remotefrom said control valve whereby pressure medium in said vent line is slowly vented to a lower pressure,

said vent line having valve means intermediate said control valve and said discharge means connected to said discharge line for closing said discharge line in response to 'flow of a pressurized medium therethrough at a pressure above said lower pressure without aflecting flow through 'said control line, and a sensing line connecting said control valve'to a portion of said compressor intermediate said inlet and said outlet for operating said discharge line operative in one condition to cause said control valve to communicate said control line and said'vent line.

3. A control circuit for isolating a multl-stage compressor wherein said compressor has an inlet and outlet with said outlet being connected to a discharge line having a high pressure medium flowing therethrough, a control valve, a control line connecting said control valve withoutaitecting flow through said control line, sensing means connected to an intermediate receiver portion of said compressor and to saidcontrol valve to causesaid control valve to; condition said control line and said'vent line into communicative relationship in response to variations in the pressure in said intermediate portion above and below atmospheric pressure resulting from the clos- 4. A control circuit for isolating a multi-stage compressor wherein said compressor is connected to a discharge line having a high pressure medium flowing therethrough to a receiver, a control valve operatively connected at one end to said discharge line through said receiver, a control line connected to the other end of said control valve, a vent line operatively connected to said control line by said control valve wherein said vent line has a discharge means at a portion thereof remote from said control valve whereby the pressure in said vent line is slowly vented to a lower pressure, said vent line having valve means intermediate said control valve and said discharge means connected to said discharge line for closing said discharge line in response to flow of a pressurized medium therethrough at a pressure above said lower pressure without affecting flow through said con trol line, sensing means connected to an intermediate receiver portion of said compressor and to said control valve to cause said control valve to connect said vent line to said control line in one position to connect said control line to said vent line, and to thereby cause said valve means to be subjected to the pressurized medium in said receiver to bias said valve means into closed position.

5. A control circuit for isolating a multi-stage compressor having an inlet and outlet with said outlet being connected to a discharge line having a high pressure medium flowing therethrough, a control valve having two difierent operating positions resulting from the opening or closing of said inlet, a control line connected to said discharge line and to said control valve, a vent line operatively connected to said control line by said control valve wherein said vent line has discharge means at a portion thereof remote from said control valve whereby the pressure therein is slowly vented to a lower pressure,

said vent line having valve means intermediate said control valve and said discharge means connected to said discharge line for closing said discharge line in response to flow of a pressurized medium therethrough at a pressure above said lower pressure without afiecting flow through said control line, and said control valve blocking said control line from being connected to any other lines when said control valve is in one position, and for connecting said control line to said vent line when said control valve is in its second position.

6. A control circuit for isolating a multi-stage compressor having an inlet and outlet, a discharge line connecting said outlet to a receiver, said receiver having an oil sump therein, a control valve connected to said discharge line through said receiver, sensing means connected to a portion of said compressor intermediate said inlet and outlet and to said valve to cause said control valve to assume a first or a second position in response to pressure variations in said intermediate portion resulting from a corresponding opening or closing of said. inlet, a first oil flow line connecting said control valve and said oil sump, a second oil flow line connecting said discharge line to said valve, said valve having an oil flow exit line, a control line connected to said discharge line and to said valve, a vent line operatively connected to said control line by said valve wherein said vent line has discharge means remote from said valve whereby the pressure therein is slowly vented to a lower pressure, said vent line having means intermediate said valve and said discharge means connected to said discharge line for closing said discharge line in response to flow of a pressurized medium therethrough at a pressure above said lower pressure without afiecting flow through said control line and said second oil flow line, said valve in said first position connecting said first oil flow line to said oil exit line and preventing said control line and second oil flow lines from being connected to any other lines when said inlet, is open, and said valve in said second position connecting said second flow line to said on exit line and said control line to said vent line and preventing V 8 said first oilflow line from being connected to any other line when said inlet is closed.

7. A control circuit for isolating a multi-stage compressor "having an inlet and outlet, a discharge line con necting said outlet to a receiver, said receiver having an oil sump therein, a control valve 'connectedjto said discharge line through said receiver, sensing means con nected to a portion of said compressor intermediate said inlet and outlet and to said control valve to causesaid control valve to assume a first position or a second posi tion in response to pressure variations in said intermediate portion resulting from a corresponding opening or closing of said'inlet, a first oil flow line connecting said valve and said oil sump, a second oil flow line connectingsaid discharge line to said control valve, said control'valve having an oil flow exitline, a control line connected to said discharge line and to said control valve, a vent line operatively connected to said control line by said control valve wherein said vent line has a restrictive opening at the end thereof remote from said valve whereby the pressure therein is slowly vented to a lower pressure, said vent line having valve means intermediate said control valve and said restrictive opening connected to said discharge line for closing said discharge line in response to flow of a pressurized medium therethrough at a pressure above said lower pressure without afiecting flow through said control line and said second oil flow line, said control valve in said first position connecting said first oil flow line to said oil exit line and blocking said control and second oil flow lines irom being connected to any other lines when said inlet is open, said control valve in said second position connecting said second flow line to said oil exit line and said control line to said vent line and blocking said first oil flow line from being connected to any other line when said inlet is closed and said valve means for closing said discharge'line having an area subjected to the pressurized medium in said receiver to bias said valve means for closing into its closed position.

8. A control circuit for isolating a multi-stage compressor having an inlet and outlet, a discharge line connecting said outlet to a receiver, said receiver having an oil sump therein, a control valve connected to said discharge line through said receiver by a first oil flow line connecting said oil sump and control valve, sensing means connected to an intermediate receiver portion of said compressor and to said valve to cause movement of said valve in response to variations in the pressure in said intermediate portion above and below atmospheric pressure resulting from the opening or closing of said inlet, a second oil flow line connecting said discharge line to said valve, an oil flow exit line connecting said valve to oil injecting means, said oil injecting means operatively connected to said compressor for injecting oil into said compressor, a control line connected to said discharge line and to said, valve, a vent line operatively connected to said control line by said valve wherein said vent line has restriction means in a portion thereof remote from said valve whereby the pressure therein is slowly vented to the atmosphere, said vent line having means intermediate said restriction means and said valve connected to said discharge line for closing said discharge line in response to flow of a pressurized medium therethrough at a pressure above atmospheric pressure Without affecting flow through said control line and said second oil flow line, said valve connecting said first oil flow line to said oil exit line and preventing said control and second oil flow lines from being connected to any other lines when said inlet is open, and said valve connecting said second flow line to said oil exit line'and said control line to said vent line and preventing said first oil flow line from being connected to any other line when said inlet is closed.

9. A control circuit for isolating a multi-stage coinpressor having an inlet and outlet, a discharge line com 9 necting said outlet to a receiver, said receiver having an oil sump therein, a, control valvehaving a first oil flow line connected to said oil sump and a-conduit1connected to said receiver, sensing meansconnected to a portion of said compressor intermediate said inlet and outlet and to said valve to cause said valve to assume a first or a second position i'n'response, to pressure variations in said compressor portion resulting from the opening or closing of said inlet, a second oil fiow line connecting said discharge line to said valve, an ,oil flowexit line connecting said valve toroil injectingmeans, said oil injecting means operatively connected to said compressor for injecting oil into said compressor, a control line connected to said discharge line and to said valve, a vent line operatively connected to said control line by said valve wherein said vent line has a restrictive opening at the end thereof remote from said valve whereby the pressure therein is slowly vented to a lower pressure, said vent line having valve means intermediate its ends connected to said discharge line for closing said discharge line in response to flow of a pressurized medium therethrough at a pressure above said lower pressure without affecting flow through said control line and said second oil flow line, said control valve connecting said first oil flow line to said oil exit line and preventing said control and second oil flow lines from being connected to any other lines when said control inlet is open, said valve connecting said second flowline to said oil exit line and said control line to said vent line and preventing said first fiow line from being connected to any other line when said inlet is closed and said exit oil flow line having a portion with means for cooling oil flowing therethrough which portion is connectible to said exit line by means responsive to the temperature of the oil flowing from said valve.

10. A control circuit for isolating a multi-stage com- A pressor having an inlet and outlet, a discharge line connecting said outlet to a receiver, said receiver having an oil sump therein, a control valve, sensing means connected to a portion of said compressor intermediate said .inlet and outlet and to said control valve to assume a first or a second position to cause said valve in response to pressure variations in said intermediate portion resulting from the opening or closing of said inlet, a first oil flow line connecting said valve and said oil sump, a second oil flow line connecting said discharge line to said valve, said valve having an oil flow exit line, a control line connected to said discharge line and to said valve, a vent line operatively connected to said control line by said valve wherein said vent line has a restrictive opening at the end thereof remote from said valve whereby the pressure therein is slowly vented to a lower pressure,'said vent line having means intermediate said valve and said restrictive opening connected to said discharge line for closing said discharge line in response to flow of a pressurized medium therethrough at a pressure above said lower pressure without aifecting flow through said control line and said second oil flow line, said valve connecting said first oil fiow line to said oil exit line and preventing said control and second oil flow lines from being connected to any other lines when said inlet is 4 open, said valve connecting said second flow line to said oil exit line and said control line to said vent line and preventing said first oil flow line from being connected to any other line when said inlet is closed, an auxiliary oil flow line connected to a portion of said receiver and to valve and said intermediate portion of said compressaid valve, an auxiliary oil flow exit line connected to said sor, and said valve connecting said auxiliary oil flow line to said auxiliary oil flow exit line only when said inlet is open.

11. A control circuit 'for isolating a two stage compressor having an inlet and outlet with an intermediate receiver therebetween with said outlet being connected to .8 discharge line having a high pressure medium flowing "10 therethrough to areceiver, said receiver having'an oil sump therein, a control valve, sensing means connecting said intermediate receiver to said control valve to cause said valve to move torone of two positions in response to pressure variations 'in said intermediate receiver resulting from the, Opening or closing of said inlet, a first oil flow line connecting said valve and said oil sump, ,a secondoil flow line connecting said discharge line to said valve,an oil flow exit lineconnecting said valve to oilinjecting means, said oil injecting means opera- .tively connected to said compressor for injecting oil into said compressor, a control line connected to said discharge line and to said valve, a vent line operatively connected to said control line by said valve vwherein said vent line has a restrictive opening in the end thereof remote from said valve whereby the pressure therein is slowly vented to the atmosphere, said vent line having means intermediate the ends thereof connected to said discharge line for closing said discharge line in response to flow of a pressurized medium therethrough at a pressure above atmospheric pressure without affecting flow through said control line and said second oil flow line,

. said valve connecting said first oil flow line to said oil exit line and preventing said control and second oil fiow lines from being connected to any other lines when said inlet is open, and said valve connecting said second flow line to said oil exit line, and said control line to said vent line and preventing said first oil flow line from being connected to any other line when said inlet is closed.

12. A control circuit for isolating a two stage compressor having an inlet and outlet with an intermediate receiver thereinbetween with said outlet being connected by a discharge line having a high pressure medium flowing therethrough to a receiver having an oil sump therein comprising, a control valve, sensing means connecting said intermediate receiver to said control valve to condition said valve in one of two positions in response to pressure variations in said intermediate portion resulting from the opening or closing of said inlet, a first oil flow line connecting said valve and said oil sump, a second oil flow line connecting said discharge line to said valve, an oil flow exit line connecting said valve to means for injecting oil into said compressor, a control line connected to said discharge line and to said valve, a vent line operatively connected to said control line by said valve wherein said vent line has a restrictive opening in the end thereof remote from said valve whereby the pressure therein above atmospheric pressure is slowly vented to the atmosphere, said vent line having means intermediate the ends thereof connected to said discharge line for closing said discharge line in response to flow of a pressurized medium therethrough at a pressure above atmospheric pressure without affecting flow through said control line and said second oil flow line, said valve connecting said first oil flow line to said oil exit line and preventing said control and second oil flow linesfrom being connected to any other lines when said inlet is open, and said valve connecting said second flow line to said oil exit line, said control line to said vent line and preventing said first oil flow line from being connected to any other line when said inlet is closed, an auxiliary oil flow line connected to a portion of said receiver other than said oil sump and said valve, an auxiliary oil flow exit line connected to said valve and said intermediate receiver portion of said compressor, and said valve connecting said auxiliary oil flow line to said auxiliary oil flow exit line only when said inlet is open.

13. A control system comprising a compressor with an inlet and a discharge line, said discharge line connects said compressor to a receiver for conducting a high pressure medium therethrough to said receiver, said receiver has an oil sump therein, a discharge valve intermediate said discharge line and said receiver, sensing means connecting said compressor to a control valve to cause said 11 control valve to assume one of two positions, said control valve having an oil exit linetherefrom, said control valve in one position having a first oil flow line connecting said oil sump of said receiver to said oil exit line, said control valve in saidsecond position'connecting a second oil line from said discharge line to said exit line, and simultaneously connecting a control line from said discharge line to a vent line mounted in said control valve, said vent line is operatively connected to'said discharge valve for biasing said discharge valve to a'closed position when said control valve is in its second operative posi- 12 tion, said vent line is further connected to a restrictive opening to atmosphere, said control valve in said second position disconnects the communication between said first oil fiow line and said sump as well as-between said dis- 6 charge line with said compressor.

References Cited in-the file of 'this patent UNITED STATES PATENTS Aikman- Nov. l, 1938 2,279,431 Aikrnan Apr. 14, 1942 Wrrrn STATES PATENT FFICE QRTEFMATE F CQECTWN Patent Noe 297 039 March 28 1961 I Willard E. Green et a1.

It is hereby certified that error appears in the above numbered patent requiring oorree'tion and that the said Letters Patent. should read as correc'bed belowm Column 9,, line 30* after "first," insert oil line 67, strike our "valve said intermediate portion of said c0mpres" and insert the same after "said", second occurrence in line 68 same column Signed and 'hhis 10th day of October 1961.,

I (SEAL),

Attest:

ERNEST W. swmra I DAVID L. LADD Arresting Officer I Commissioner of Patents USCOMM-DC-

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