US2386038A - Fluid pressure mechanism - Google Patents

Description

Oct. 2, 1945.

W. A. EATON FLUID PRESSURE MECHANISM Filed Aug. 4, 1943 2 Sheets-Sheet 1 I mmvrox.

* amawm z, ATTORNEY FLUID PRESSURE MECHANISM med Aug. 4,1945 2- Sheets-Sheet 2 (ii E 5+ T oooooo o R Q Q -2 Q "2 V JNVgNmR. V) v a WiyredA-Eaiom Patented Oct. 2, 1945 NT." i OFFICE FLUID PRESSURE MECHANISM Wilfred A. Eaton, Elyria, Ohio, assignor t6. Ben;

dix-Westinghouse Automotive Air Brake C'o mpany, Elyria, Ohio, a corporation of Delaware Application August 4, 1943, SerialNo. 497385 20 Claims.

This invention relates to fluid pressure supply systems and more particularly to mechanism for supplying fluid pressure under substantially high pressures and for controlling the maintenance of these pressures. The present invention contemplates a mode of operation wherein the intake side of the fluid compressor is normally maintained at a pressure well above atmospheric pressure, this mode of operation permitting the compressing of fluids to a relatively high pressure at the output side of the compressor without resulting in a correspondingly increased compression ratio, such as would occur, for example, in the event such a high pressure were obtained from a single stage compressor in the ordinary manner. 7 In addition to the foregoing, the present invention contemplates a system wherein, after the system has been initially charged with fluid pressure, the system automatically becomes a closed system, no further fluid being drawn into the compressor from an outside source except such fluid as is necessary to compensate for any leakage from various parts of the system, systems of this nature being particularly applicable to the compression of air wherein the moisture always present in atmospheric air often times has a very detrimental eiTect on the opera tion of the system, an efiect which is largely minimized by the present invention.

It has previously been proposed to provide socalled closed systems for the compression of air or other fluid in order to prevent the accumulation of excessive moisture in the system such as might be drawn in from the atmosphere, but difliculty has been experienced in systems of this type in properly controlling the pressures in the low and high pressure portions of the system, and it is accordingly an object of the present invention to provide means for controlling the pressures in the system Without attention on the part of the operator.

Another object of the invention is to provide, in a fluid compressing system of the above type, means for maintaining the intake side of the compressor at a pressure above that of the surrounding atmosphere.

A further object of the invention is to provide, in a fluid pressure supply system having low and high pressurereservoirs, means for initially charging both reservoirs and for subsequently recompressing the fluid supplied to the low pressure reservoir in order to supply fluid at a higher pressure to the high pressure reservoir.

A still further object of the invention is to provide, in a system of the above type, means for conreservoir except whensuper-charged trolling the pressures in the low and high pres: sure reservoirs. so constituted as to rendersit unnecessary for Ithe compressor to. operate directly against the high .pressureinuthe highpressure with fluid from the' low pressure reservoir. u P 1 Yet another object of the. invention is to pro-' vide, in a system of the above type, control means responsive to. variations in pressure in: both the low and high pressure reservoirs for automatically insuring replenishment of thefluid in eitherres ervoir in the event of leakage therefrom.

A further object of theinvention isto'iprovide, in a system ofthe above type, means for unload- ,ing thecompre'ssor and preventihgthe supplying of fluid to eitherr'eser'voir whenever the pressures in the reservoirs exceed predetermined values; Still another'object oftheinvention is to provide, in asystem oftheZabovetypejmeans for controlling the establishment and maintenance of predetermined pressure ratios between the lo'w and high pressure t'reservoirs of the system by means of a singlefluid pressure operated control valve. r

Yet another object of theFinvention is to pro vide, in a system of the above type, control means for the compressor so constituted as to permit initial parallel charging 'of the low" and high pressure reservoirs, and: subsequent alternate charging of one reservoir or the other dependent on the pressure ratio obtaining in the low and high pressure reservoirs. A it 'These and other objects and novelfeatures of the invention-will appear more fullyhereinafter from the following detailed description when con sidered: in connection with the accompanying drawings, wherein two embodim'eiitsof the invention are illustrated. a. a a.

It is'to be expressly' understood, however, that the drawings are employed for purposes of illustration only, and are not designed as a definition of the limits of the invention; reference for-this purpose being had to .therappended claims.

In the. drawings, wherein similar reference 'nu merals denote corresponding elements throughout the severalviews: V

Fig; 1 is a diagrammatidshowing, Dartiallyin section, of a fluidpressure' supply system embody ing the principles of the present invention,;and

Fig. 2 is a diagrammaticillustration, Partially in section; of another embodiment of the invention.

Referring more particularlyto Fig. 1' of the drawings,ya fluidpressu're supply system embo'dy ing the presentinvention is illustrated therein as including ailowpressure:reservoir::6 and a high connected therewith and a one-way check valvel3 having a connection [4 to atmosphere orto any other desired source of fluid pressure, it being understood that the check valve is so constituted as-to permit the flow of fluid pressure from the prevent the flow of fluid pressure in theoppositei direction through said connections. The outlet port 9 of the compressor is connected with thelow' pressure reservoir 6 through a Tconduit l andaconduit I6, the latter being connected as shown by means of a control valve mechanism IT to be more fully described hereinafter. v pressure may be supplied directly to the high pressure reservoir 1 from the compressor, the conduit l5is connected to the latter by means of conduits l8 .and 19, the latterconduits beingv connected through the medium of a one-way check valve 20, so constituted as to permit the fiowof fluid pressure from conduit [8 to conduit I9 and to prevent the flow of fluid pressure vtherethrough in the opposite direction.

The valve mechanism I1" is provided with a casing 2 I, the casing being provided with a chamher. 2 la connected with conduit1l5, a chamber 2 lb connected with the low pressure reservoir through the conduit 16 and a chamber 2 le connected: with the inlet port of the compressor through con duit H. The chambers to and 2H) are'separated by means of a partition 22 provided with a centrally located port 23, while the chambers 2 lb and 210 are separated by means of a partition 24 provided with a centrally located port 25, the lat ter port being normally closed by means of a valve '26 provided withzan upwardly extending stem 21 connected at. its upper end with a diaphragm 28 clamped to theupper end of the housing by means of a cover plate 29 suitably bolted thereto. The valve is normally maintained in the position shown by means of a'spring30 interposed between the lower face of the diaphragm and the upper surface of a partition 3! which serves to define the upper end of the chamber 2 lo, leakage .from the 'chamber2lc around the valve stem 21 being prevented by means of a suitable sealing element 32 as shown. The cover plate 29 defines, in connection with the diaphragm 28, a control chamber 33,-a'nd it will be understood that on application of fluid pressure to the control chamber, the tension of the spring 30 will be overcome and the valve '26 will be moved downward to open' the port 25 and close the upper end of the port 23. Other means are also provided for controlling the operation of the valve 26 including a second dia phragm 34 clamped to the lower end of the casing by means of a cover plate 35,. the latter forming in connection with the diaphragm a second control chamber '36. The diaphragm is normally maintained in the position shown by means of a spring 3! interposed between the upper face of the diaphragm and the-lower face of a partition 38 which serves to define the lower end of the *chamber 21a, and a valve operating stem 39 is suitably attached to the central portion of the diaphragm as shown and slidably'mounted in the partition 38, leakage by the stem from the lower end or the chamber 2m being prevented by means'of a suitable sealing element 40, as shown.

The diaphragm andvalve pperating stem are nor In order that fluid.

..lower face of the partition 38. 2 so positioned that with the stem in its extreme I 5i mally maintained in the position shown by means of the spring 31, the upper end of the stem 39 being so positioned with respect to the port 23 as to permit movement of the valve 21 to a position to close the upper end of the port under the action of the upper diaphragm 28. On application of fluid pressure to the control chamber 36, the valve stemisrmoved upward against the tensiorrof the spring 31, it being noted that the degree of upward travel of the valve stem 39 is t limited by means of a shoulder 4| formed thereon atmosphere to the inlet of the compressor, and to and adapted on upward movement to engage the This shoulder is upward p'osition-,fthe upper end of the stem serves .to prevent movement of the valve 26 into a position to close the port 23 on application of pressure to chamber 33, in such a manner that the chamber- 2Ib is connected at the same time with the chamber 2Ia, the chamber Zlc and the conduit l5 connected with the low pressure reservoir.

In order to control the operation of the valve mechanism ll, a governor of well-known type designated as 42 is associated with the low pressure reservoir, being connected with the reservoir by means of a'conduit 43 and with the control chamber 33 of the valve by means of a conduit 44, it being understood that the governor is so constructed as to normally prevent communication between conduits 43 and 44 and to permit communication between conduit. andan exhaust-port not shown, an increase in the pressure supplied to the governor throughthe conduit 43 beyond 'a' predetermined value serving to operate thelatterj to prevent communication between the conduit 44 and the exhaust port and to establish com munication betweeio the conduits 44 and 43 in order to supply fluid pressure from the reser voir to the control chamber 33. In like manner, a'second governor 45 of similar construction is associated with the high ressure reservoir, being connected with the reservoir through a conduit 46 and-with the lower control chamber 36 through a conduit-41, it'being noted that this governor actsin' the same manner as the governor 42 to normally establish communication between the conduit 41 andan exhaust port, not shown, and to prevent communication between conduits 46 and 41 the governor being efiective when a predetermined pressure is reached in the reservoir 1 to dises tablish the connection between the conduit Wand the atmospheric port and to establish a connection between conduits 4i and 46 to supply fluid pressure from the highv pressure reservoir Ito the control chamber 36.

In view of the foregoing description, it will be understood that during initial operation of the compressor to charge the system with fluid pressure, both of'the control chambers 33 and 3-6 will be connected with atmosphere through the operation of the governors 42 and .45, and fluid pressure will be. drawn in from atmosphere through the conduit 4, the check valve l3, the conduit 12, conduit H and inlet port It, and supplied to the low pressure reservoir through the outlet-port 9, theconduit '85, the chamber Zia of the valve ll, open port 23, chamber 21b and conduit it, while at the same time, fluid pressure will be supplied to the high pressure reservoir I through conduit l5, conduit iii, check valve 29 and conduit xi 9, it being understood that the flow of fluid in the reverse direction from the high pressure reservoirto the compressor is prevented bythe .check valve 29'. during initial operation of the compressor, both of the reservoirs are and the inlet port of the compressor through conduit l6, chamber 2th, port 25, chamber He and conduit H. Thus when the predetermined pressure for which the governor 42 is adjusted is established in the low pressure reservoir, the fluid already stored in the reservoir is returned to the inlet port of the compressor in order to supercharge the compressor, the check valve I3 during this type of operation serving to prevent the flow of fluid pressure to atmosphere from the low pressure reservoir. Since the connection between the compressor and the high pressure reservoir is normally open in one direction, however, the compressor will continue to supply fluid pressure to the high pressure reservoir until such time as the pressure in the low pressure reservoir is depleted sufiiciently to cause the governor 42 to operate to again disconnect conduits 4'4 and 43 and connect 1 condut 44 with atmosphere-whereupon the valve will return to the position shown and the low pressure reservoir will again be charged with fluid drawn in through the atmospheric inlet. As this action continues, it will be evident that the high pressure reservoir will eventually reach a pres sure sufiicient to operate the governor 45, this governor preferably having a setting substantially higher than that of the governor 42, and when this pressure is reached, the governor 45 will be effective to dis-establish communication between conduit 4! and atmosphere and to connect conduits 41 and 46 to supply fluid pressure to the control chamber 36, and since the pressure supplied to the chamber 36 from the reservoir 1 is appreciably higher than that supplied to the control chamber 33 from the reservoir 6, the valve operating stem 39 will serve to prevent movement of the valve 26 beyond mid-position in the chamber 2ib through the operation of the diaphragm 28. The above may be called the second phase of operation wherein the compressor operates under the control of the valve mechanism I! to al ternately supply fluid pressure from the low pressure reservoir to the high pressure reservoir and to supply fluid pressure from atmosphere to the low pressure reservoir in order to make up for the fluid pressure supplied from the low pressure reservoir to the high pressure reservoir. When a pressure in the reservoir I is reached such that the governor 45 becomes operative to connect the conduits 41 and 46, however, it will be apparent that a third phase of operation will be established wherein the valve 26 is moved to mid-posi tion to establish a connection between the inlet and outlet ports and the reservoir 6, all the fluid pumped by the compressor during this phase of operation being recirculated through the inlet of the compressor through chamber 2la, port 23, chamber 2lb, port 25, chamber 210 and conduit ll, these conduits being maintained at the same pressure as the low pressure reservoir by virtue of the connection l6 between the chamber 2th and the reservoir 6. Thus a condition of equilibrium will be established wherein a relatively low prestermined value.

sure is established in the low pressurereservoir controlled by. the setting of the governor 42, while a relatively high pressure is established "in the reservoir 1 controlled by. the setting of thegovernor 45, the compressor being ineffective when this condition is established to supply further fluid pressure to either of the reservoirs in view of the connection established between'the inlet and outlet ports. i i

. Since it is possible that leakage may occur from either of the reservoirs, it is desirable in a system of this type that the control means be so constituted as to control the operation of the compressor inorder to immediately render the latter effective to compensate for any leakage from either reservoir, and with further reference to the, drawings, it will be noted that with the system-in equilibrium as above described, leakage offluid pressure from the low pressure reservoir when the governor 45 is effective to supply fluid pressure from the high pressure reservoir to the chamber. 36, willserve eventually to actuate the governor 42 to dis-establish the'connection between conduits 44 and 43 and connect the conduit 44 with atmosphere, whereupon the valve 26 will be returned to the position shown with the result that the compressor will again be effective to draw fluid from the atmosphere and supply it to'the low pressure reservoir through the passages above described. In like manner with the valve 26 again in mid-position and the compressor in the unloaded condition by virtue of the control exercised by the above valve, it will be seen that a decrease in the pressure inthe reservoir 1 due to leakage will result in operation of the governor 45 to disconnect conduits 41 and 46 and connect conduit 41 withatmosphere, whereupon the pressure in the chamber 33 will be effective to move the valve 26 downward to close the upper end of the port 23 in order to connect the low pressure reservoir with the inlet port of the compressor, whereupon the compressor will be supercharged and will supply fluid pressure at a higher pressure to the reservoir 1 in order to compensate for the leakage, the governor 45' again being effective to return thevalve 26 to the unloading position when the pressure in the reservoir 1 reaches the aforementioned prede- In the event the pressures in both reservoirs drop sufiiciently to cause the governors 42 and 43 respectively to be efiective to connect the conduits 44 and 41 with atmosphere, the parts of the valve I! will return to the position shown in the drawings, and the compressor will operateto draw fluid from the atmosphere and compress, it in the reservoir 6 until such time as the governor 42 again becomes operative to actuate the valve 26. 7

As heretofore described, the compressor is effective during initial operation with the parts of the valve I! in the position shown, to charge the reservoirs B and 1 in parallel through the connections described until such time as the governor 42 becomes effective to move the valve 26 to con: nect the low pressure reservoir with the inlet of the compressor, whereupon a supercharging action occurs wherein the fluid from the low pressure reservoir is compressed and delivered to the high pressure reservoir, the valve 26 again being returned to the position shown when the low pressure reservoir is sufliciently depleted to a ain actuate the governor 42 to connect conduit 44 with atmosphere. When a predetermined higher pressure is established in the reservoir 1, the governor 45 becomes operative to energize the valve pedal.

outlet 53' of the brake valve is connected with the diaphragm M to prevent movementoi the valve 26 to its downward position, with the result that the valve 2-16 can only be moved to mid-position to permit recirculation of the fluid from the discharge port of the compressor to the inlet port of the compressor, no fluid being pumped to the reservoirs under this condition of operation Leakagein either of the reservoirsserves to so control the operation of the valve H as to cause the'compressor to pump-suflicient fluid tothat reservoir to replace leakage, thevalve thereafter being operated under the controlhof one or the other'or both of the governors to place the compressor "in the unloading condition until further fluid leaks or is utilized from the system.

The system is illustrated in connection with a simplified brake system comprising a fliud'brake actuator "48 having a piston 49 and a piston rod 50 attached thereto foractuating the brakes. The operation ofthis actuator 'is controlled by means of an operators control valve '51, which may be constructed in accordance with the principles set forth in the patent to Wilfred A. Eaton, No. 2,204,530, dated Ju-ne l1, l-940,'this valve being provided with an inlet connection 52 connected with the high pressure reservoir 1 through a conduit 53 and an outlet connection 54 connected withithe actuator through a conduit 55. The valve is" also provided with an exhaust connection 56 co'nnectedwith' the low pressure reservoir through conduit andon reference to the above patent, it will be understood that a brake pedal -58 pivotally" mounted on the=valve 51 by means of a suitable pin 59 serves to operate the brake valve in the position shown to establish a connection between conduits 5'5Zand 51 and to pre vent communication between conduits'53 and 55, downward movement of the pedal serving todisestablish the connection between the conduits 55 and 5''! and to establish communication between conduits 53 and 55 to supply fluid pressure to the motor 18 in an amount substantially proportional to the degree of'movement of the brake In view of the fact that the exhaust low pressure'reservoir, it will be apparent that any'fluid utilized from thehigh pressure reser-' voir to operate the fluid motor is returned to the low pressure sideo'f the system ratherthan to atmosphere, with the result that fluid from the atmosphere is pumped into the low pressure reservoir'only-when needed to replace leakage occurring in various parts of the system. Since the low pressure reservoir and consequently the exhaust conduit 51- and the'outlet conduit 55 of thecontrcl-valve are at all times at a' pressure higher than atmosphere, the motor 4-8 is provided with a piston return'spring Gil so tensioned as to be capable under all conditions of returning the piston 49 to the position shown when the valve 5! is operated to release fluid pressure from the motor, this spring therefore being sufficiently strong to overcome the back pressure in the system at all times. r 7

During some types of operation, it is unnecessary to provide means for unloading the compressor when the pressures in the'low and high pressure reservoirs reach their predetermined maximums; and another embodiment of the invention, illustrated in Fig. 2 of the drawings, provides for this type of operation. As illustrated, the system shown in Fig. 2 includes: a low pressure reservoir 6 and a hi h pressure reservoir l, together with a fluid compressor 8, the compressor being provided with a discharge connection 9 and an'inlet connection Hi, the latter being adapted to receive fluid .fromrthe atmosphere through a conduit H, a conduit l2 connected therewith and a one way check valve 13 having aconnection M to atmcsphere, it beingimderstood that the check valve is so constituted as topermit the flow of fluid from the'atmosphere'to-the inlet of the compressor, and to prevent the 'flow of fluid pressure inthe opposite direction. The outlet port!) of the compressor, is connected with the low pressure reservoir 6 through a conduit l5 andagconduit 1-6, the. latter conduits being connected as shown by means of a control valve mechanism 61, to be more fully described hereinafter. In order that fluid pressure may be supplied directly to the high pressure reservoir 1 from the compressor, the conduit is is connected to the latter by means or conduits I8 and 19, the latter conduits being connected through'the medium of a one waycheck "valve 26, so constituted as to permit the flow of fluid pressure from conduit 18 to conduit l9 and to prevent the flow of fluid pressureitherethrough in the opposite direction A fluid actuator or motor '48 is preferably constructed in the same manner asthat illustrated in Fig. 1, means for supplying fluid pressure to the mot-or from the-high pressure reservoir 1 including the control valve-5i, connected with the high pressure reservoir through conduit 53, with the fluid motor through conduit 55, and with the low pressure reservoir through an exhaust conduit 51, it being understood that the control valve is effective in the same manner as illustrated in Fig. 1 to control the pressure of fluid supplied to the fluid 'motorand to permit the return of any fluid exhausted to the low pressure reservoir'in order to'prevent loss of the fluid from the system. The connection between the exhaust conduit 51 and the low pressure reservoir t is completed by means of a conduit 52 inter connected therebetween.

The valve mechanism 5! is provided with a casing 63, this casing being provided with chamber 64 connected with the conduit i5, 2. chamberGS connected with the conduit l6, and a chamber 66 connected'with the conduit H leading to the inlet port of the compressor, the charm bers 64 and 65 being separated by means of a partition 61 provided with a centrally located port 68, and the chambers 65 and 66 being separated by means of a partition: 69 provided with a centrally located port H1. The port 68 is normally openwhile the port IQ is normally closed at its lower end by means of a valve ll carried on the lower end of a valve stem 12 slidably mounted in a partition 73 which serves to close the upper end of the chamber 65. A pressure responsive means or diaphragml i is suitably attached to the'upper end of the valve stem as shown, the outer periphery of the diaphragm being clamped between the casing fi3 and a coverplate '55 bolted thereto as shown, the diaphragm serving to define in connection with the casing, the partition 13, and the'cover plate (5, an atmospheric chamber l6 located below the diaphragm and connected with atmosphere by mean of a port Ti, and acontrol chamber 78 above the diaphragm adapted to receive fluid pressure from the reservoir 6 as will be more fully described hereinafter. The valve and diaphragm are normally maintained in the position shown by means of a spring 79 interposed between the upper surface'of the partition 13 and the lower surface of the diaphragm 14, it being apparent that when fluid pressure is s pplied to the control chamber 18, the diaphragm and valve will be moved downward against the force ;ex erted by the spring 19 in order to move the valve to a position to open the port 10 and to close the upper end of the port 68. The application of fluid pressure from the low pressure reservoir to the control chamber 18 of the valve 6| is controlled by means of the governor 42 which may be identical with the governor 42 illustrated in Fig. 1, the governor being connected with the low pressure reservoir by means of the conduit 43 and with the control chamber 18 by means of the conduit 44, it being understood'in View of the description relatingto Fig. 1 that the governor is normally effective to prevent communi cation between conduits 43 and 44 and to per:

mit communication of the conduit 44 with at mosphere, While in response to an increase in pressure in the low pressure reservoir above .a

predetermined value, the governor is operative to establish communication between conduits 4 3 and 44 to supply fluid pressure to the control chamber 18 at the same pressure as that obtaining in the low pressure reservoir, the governor being further effective on a predtermined decrease in pressure in the reservoir below the predetermined value, to again reverse the above operation to exhaust fluid pressure from the con trol chamber 78.

In order that the pressure in the high pressure reservoir may be satisfactorily controlled, a pressure regulator valve 80, of Well-known type, is interconnected between a conduit 8! connected with the high pressure reservoir and the conduit 51, which, as heretofore described, is connected with the low pressure reservoir through the conduit 62. The pressure regulator valve 80 is provided with an adjusting screw 82, and is so constituted as to establish a connection between conduits 8i and 51 when the pressure in conduit 8| is higher than the pressure in the conduit 51 by a predetermined value, and to dis-establish the above connection when the pressure diiferential drops below the predetermined value. The valve may be thus adjusted in such a. manner as to prevent the flow of fluid pressure from the reservoir 1 to the reservoir 6 except when the pressure in the high pressure reservoir exceeds that in the low pressure reservoir by the desired value. Thus in the event excess fluid is pumped into the high pressure reservoir 1, the valve 80 is operative to exhaust this fluid to the low pressure reservoir without loss of fluid to atmosphere.

On initial operation of the compressor with atmospheric pressure in both the low and high pressure reservoirs, the discharge port 9 of the compressor is connected with the low pressure reservoir through conduit 15, chamber 64, port 68, chamber 65 and c0nduitl6, the port being connected at the same time with the high pressure reservoir through conduit '18, the one way check valve and the conduit l9, andit willbe understood that the compressor will'draw in fluid from the atmosphere through the conduit l4, the check valve 13, conduits I2 and II and inlet port II), the fluid being free to pass from the compressor directly to both of the reservoirs through the connections above described. When'a pressure is established in the low pressure reservoir sufficient to operate the governor 42 to establish a connection between conduits 43 and ,44, the fluid pressure supplied to the' control chamber 18 will serve to operate the valve Htto'open the port 10 and close the port 68. When'the port port 10, chamber 66 and conduit II, the fluid thus supplied to the compressor serving to supercharge thelatter and to permit the pumping of a relatively high pressure to the high pressure reservoir, and at the same time permitting the compressor to operate at a relatively low compression ratio. This action will continue until the pressure in the low pressure reservoir drops sufiiciently to operate the governor in the reverse direction, whereupon the compressor will again become effective to pump fiuidfrom the atmosphere to the low pressure reservoir. Asthe pressurein the low pressure reservoir again increases, the cycle is again repeated until such time as a relatively high pressure is established in the high pressure reservoir, it being noted that when the pressure in the highpressure reservoir exceeds that of the low pressure'reservoir, fluid will no longer be supplied to the high pressure reservoir through conduit I8, check valve 20 and conduit l9 when the parts of the control valve 6| are in the position shown, as the check valve will be held in closed position by the pressure in the conduit I9 and the pressure in the conduit l8 will be insuflicient to open the check valve except when the compressor is supercharged with fluid from the low pressure reservoir. When the desired high pressure is established in the reservoir 1, this pressure will act to operate the valve to establish communication between conduits 8| and 51, and any further fluid compressed in the reservoir 1 willthus be returned to the low pressure reservoir and thence recirculated to the high pressure reservoir through the compressor. Thus the pressure which may be established in the high pressure reservoir is automatically limited to a predetermined value and the use of an atmospheric safety valve, which would result in the loss of fluid pressure from the system, is rendered unnecessary.

A simple and efficient fluid pressure supply system'has thus been provided so constituted as to charge both reservoirs inparallel until a prelow pressure reservoir thus being under the control of the governor 42 and the control valve 6! and the pressure in the high pressure reservoir being limited and controlled by means of the pressure regulator valve 82 which is responsive to variations in pressure in the high pressure reservoir.

While two embodiments of the invention have been illustrated herein with considerable particularity, it is to be understood. that the same is not limited to the formsshown but may receive a variety of mechanical expressions which will'be readily apparentto those skilled in the art. Reference will, therefore, be had to the appended claims for a definition of the limits of the invention.

Whatisclaimedisr f r 1. The combination in a fluid pressure supply system having lowand high-pressure reservoirs and a compressor provided with inlet and discharge ports, of means for supplying fluid, pressure from the compressor to said reservoirs including a normally open connection between the discharge port and the low pressure reservoir, a normally open connection between the discharge port and thehigh pressure reservoir, and means responsive to variations in pressure in the low pressure reservoir for closing the first named con nection when the 'pressure in-said low pressure reservoir exceeds a'p-redetermined value.

' 2 The combination in a fluid pressure supply system having low-and high pressure reservoirs and a compressor provided with inlet and dischargeports, of-means for supplying fluid pressure from thecompressor tosaid-reservoirs including a normally-open connection'between said discharge port and the low pressure reservoir, a normally open connection between said discharge port and the high pressure-reservoir, means associated with-the second named connection for preventing the-flow of fluid pressure from the high pressure reservoir to the low pressure reservoir through the first named connection, and means controlled by the variations in pressure in the low pressure reservoir for closing the first named connection when the pressure in said low pressure reservoir exceeds a predetermined value.

3. The-combination in a fluid pressure supply system having low ancl -high.- pressure reservoirs and a compressor provided with inlet and discharge ports, of means for "supplying fluid pressure from the compressor to said reservoirs including a normallyopen connection between said discharge portand the low pressure reservoin'a normally open connection between said discharge port and the high pressure reservoir, a normally closed connection between the low pressure reservoir andtheinlet portof the compressor, and valvular means controlled'by variations in pressure in the lowpressure reservoir for closing the first named connection and opening the third named connectionwhen the pressure in said low pressure reservoir exceeds'a predetermined value. 4..The combination in: a fluid pressure supply system havingilow rand highepressure reservoirs and a compressorv provided with inlet and dis.- charge ports, .of' means for. supplying fluid pressure from the compressor vto said reservoirs including a normally open connection between said discharge port andlthellow pressure reservoir, a normally open connection between said discharge port and the highpressure reservoir, a

normally closed connection between the low pressure reservoir and the inlet port of the compressor, valvular means controlled by variations in pressure in the low pressure reservoir for closing thefirst named connection and opening the last named connection when the pressure in said reservoir exceeds a predetermined value, and

' means responsive to variations in pressure in the high pressure reservoir for establishing a connectionbetween the high pressure reservoir and the low pressure reservoir when the pressure in said high pressure reservoir exceeds a higher pre determined value.

5. The combineltioriin a fluid pressure supply system having low and high pressure reservoirs and a compressor provided with inlet and discharge ports', of means for supplying fluid pressure from the compressor to said reservoirs including a normally open connection between the new discharge port of the compressor and both reservoirs, means associated with said connection and controlled by variations in pressure in the low pressure reservoir for preventing the flow of fluid pressure from the discharge port to the low pressure reservoir when the pressure in said res ervoir exceeds a predetermined value, and for connecting the low pressure reservoir with the inlet port of the compressor, and means respontive to variations in pressure in the high pressure reservoir for limiting the pressure supplied thereto to a higher predetermined value.

6. The combination in a fluid pressure supply system having low and high pressure reservoirs and a compressor provided with inlet and discharge ports, of means including connections between the discharge port and the low and high pressure reservoirs for normally supplying fluid pressure to both reservoirs, means for preventing the supply of fluid pressure to the low pressure reservoir when the pressure therein exceeds a predetermined value and for supplying fluid pressure from said reservoir to the inlet port of the compressor, and means for returning fluid from the high pressure reservoir to the inlet of the compressor through the low pressure reservoir when the pressure in the high pressure reservoir exceeds a second higher predetermined value.

'7. The combination in a fluid pressure supply system having low and high pressure reservoirs, of means for transferring fluid from a source to both reservoirs to establish one pressure therein and from the low pressure reservoir to the high pressure reservoir to establish a higher pressure in the latter reservoir including a compressor having inlet and discharge ports, normally open connections between the discharge port and both reservoirs, a normally closed connection between the low pressure reservoir and the inlet port, and means controlled by variations in pressure in the low pressure reservoir for closing the connection between the discharge port and the low pressure reservoir and opening the connection between the low pressure reservoir and the inlet port when the pressure in the low pressure reservoir exceeds said one pressure. v l

8. The combination in a fluid pressure supply system having low and high pressure reservoirs and a compressor having inlet and discharge ports, of means for controlling the pressure delivered to said reservoirs by, the operation of said compressor including an open connection between the discharge port and the high pressure reservoir, means including a valve operable in one position for establishing'a connection between the discharge port and the low pressure reservoir, in a, second position to establish a connection between the low pressure reservoir and the inlet and discharge ports, and in a third position to prevent communication between the low pressure reservoir and discharge port, means for normally maintainingthe valve in the first position, means controlled by variations in pressure in the low pressure reservoir for moving the valve to the third position when the pressure in the low pressure reservoir exceedsa predetermined value, and means controlled by the variations in pressure in the high pressure reservoir and operable when the pressure therein exceeds a, predetermined value for permitting movement of the valve from the first position to the second position and preventing movement of the valve to the third position. i 7

9. The combination in a fluid pressure supply systemhaving low and high pressure reservoirs and a compressor-having inlet. and discharge ports, of means for controlling the pressure de: livered to said reservoirs by the operation of said compressor including an open connection between the discharge .port and thehigh pressure reservoir, means including a valve operable, in one position for establishing a connection between the discharge port and the lowpressure reservoir, in a second position to establish a connection between the low pressure reservoir and the inlet and discharge ports, and in a third position to prevent communication between the low pressure reservoir and the discharge port, means for normally maintaining the valve in the firstposition, means controlled by the pressure in the low pressure reservoir for, moving the valve to the third position when the pressure in said reservoir exceeds a predetermined value, and means controlled by the pressure in the high pressure reservoir for moving the valve from the third to the second position when the pressure in the latter reservoir exceeds a predetermined value. a I r a i 10. The combination in a fluid pressure supply system havinglow and high pressure reservoirs and a compressor provided with inlet and discharge ports, of means for supplying fluid pressure from the compressor to said reservoirs including a normally open connection between the discharge port and the low pressure reservoir, a normally open connection between the discharge port and the high pressure reservoir, and valvular means responsive to variations in pressure in the low pressure reservoir for closing the first connection when said pressure exceeds a predetermined value and for opening said connection when said pressure drops to a lower predetermined value. 7

11. The "combination in a fluid pressure supply system having low and high pressure reservoirs and a compressor provided with inlet and discharge ports, of means for supplying fluid pres.- sure from the compressor to said reservoirs, including normally open connections between said discharge port and both said reservoirs, means including a valve controlled by variations in pressure in the low pressure reservoir for closing the connection between the discharge port and the low pressure reservoir when the pressure in the latter reservoir exceeds a predetermined value, and means responsive to variations in pressure in the high pressure reservoir for connecting the high and low pressure reservoirs when the pressure in the high pressure reservoir exceeds a predetermined value.

12. The combination in a fluid pressure supply system 'having low and high pressure reservoirs and a compressor provided with inlet and discharge ports, of means for supplying fluid pressure from the compressor to said reservoirs in-' cluding normally open connections between said discharge port and both reservoirs, means including a connection for returning fluid pressure exhausted from the high pressure reservoir to l the low pressure reservoir, and means controlled by variations in pressure in both reservoirs for controlling the flow of fluid in said connections whereby the pressures in said low and high pressure reservoirs are substantially maintained at predetermined low and higher pressures respectively.

. 13. The combination in a fluid pressure supply system having low and high pressure reservoirs and a compressor provided with inlet and disreservoirs for controlling the'flow of fluid pressure in said connections. i

14. The combinationin a' fluid pressure supply system having low and high pressure reservoirs and a compressor. provided'with inlet and discharge ports, of means for supplying'fiuid pressure from the compressor to said reservoirs and for establishing and maintaining a substantially predetermined ratio of low and higherpressures in said low and high pressure reservoirs respectively including normally open connections between said discharge port'and both-said reservoirs, means including a connectionfor returning fluid exhausted from the high pressure reservoir to the low pressure reservoir,=me'ansfor establishing a connection between the low pressure reservoir and the inlet port' of the compressor, and meansincluding valvular means responsive to variations in pressure in both said reservoirs for controlling the flow of fluid pressure in said connections.

15. The combination in a fluid pressure supply system having lowand high pressure reservoirs and a compressor provided with inlet and discharge ports, of means for supplying fluid pressure from the compressor to said reservoirs-including a normally open connection between the discharge port and the highpressure reservoir, a normally open connection between the discharge port and the low pressure'reservoir, anormally closed connection between the low pressure res ervoir and the inlet port of the compressor, valvular means for controlling the flower fluid pres sure in said connections including a valve mov able to one position to close the connection between the dischargeport andthe low pressure reservoir and open the connection between the low pressure reservoir and the inlet port and to another position to establish a connection between the discharge port, the lowpressure reservoir and the inlet port, and means controlled in response to variations in pressure in both reservoirs for moving said valve from the last na'med position whenever the pressure in either reservoir drops below a predetermined value.

16. The combination in a fluid pressure supply system having low and high pressure reservoirs and a compressor provided with inlet and discharge ports, of means for supplying fluid pressure from the compressor to said reservoirs including a normally open connection between the discharge port and the high pressure reservoir, a normally open connection between the discharge port and the low pressure reservoir, means including a valve movable to one position to close the second named connection and to another position to establish a connection between the discharge port and the inlet port of the compressor to prevent the supplying of fluid pressure to either reservoir by the compressor, and means controlled by variations in pressure in the low pressure reservoir for moving said valve to the first named position when the pressure in the low pressure variations in pressure in the high pressure reservoir for moving said valve to the last. named position whenthe pressure in the high pressure reservoir exceeds a higher predetermined value whenthevalve-has been moved to the first. named position by the operation of the above named means.

17. The combination in a fluid pressure supply system having low and high pressure reservoirs and a compresso provided with inlet and discharge ports, oi means for supplying fluid pressure from the compressor to said reservoirs including a normally open connection between the discharge port and the low pressure reservoir, a normally open connection between. the discharge port and the highpressure reservoir, a normally closedv connection between the low pressure res- I ervoir and the inlet port, and means responsive to variations in, pressure in the low pressure reservoir for closing the first named connection, and opening the last named connection when the pressure in said'low pressure reservoir exceeds a predetermined value.

l8.v The combination a fluid pressure supply system having low and high pressure reservoirs and; a compressor provided with inlet and discharge ports, of means for supplying fluid pressure'firom the compressor to said reservoirs including a normally open connection between the discharge port andthe low pressure reservoir, a normally open connection between the discharge port and the high pressure reservoir, means for preventing the flow of fluid pressure from the high pressure reservoir to the. discharge port through said second named connection, a normally closed connection between the low pressure reservoir and the inlet port oi the. compressor, andmeans responsive to variations in pressure in the low pressure reservoir for closing the first named connection and opening the last named. connnection when the pressure in said 10w pressure reservoir exceeds a predetermined value.

19 The combination in a fluid pressure supply 7 system. having. low and high pressure reservoirs and a. compressor provided with inlet and discharge ports, of means for supplying fluid pressure from the compressor to. said reservoirs inreservoir exceeds a predetermined value and by eluding a normally open connection between the discharge port and the low pressure reservoir, a normally open connection between thedischarge port and the high pressure reservoir, a normally closed connection between the low pressure reservoir and the inlet port of the compressor, means including a valve responsive to variations in pressure in the low pressure reservoir for closing the first named connection and opening the last named connection when the pressure in said low pressure. reservoir exceeds a predetermined value, and means including a valve controlled by variations in pressure in the high pressure reservoir for supplying fluid pressure from the high pressure reservoir to the low pressure reservoir when the pressure in the; high pressure reservoir exceeds a higher predetermined value.

20. The combination in a fluid pressure supply system having low and high pressure reservoirs and a compressor provided with inlet and discharge ports, of means for supplying fluid pressure from the: compressor to said reservoirs and for maintaining the pressure in said low and high pressure reservoirs at substantially predetermined low and higher values includinga normally open connection between. the discharge port and the low pressure reservoir, a normally open connection between. the: discharge port and the high pressure reservoir, a normally closed connection betweenthe low pressure reservoir and the inlet port of the compressor, means including a valve operable in one position. to close the last: named connection, another position to close the first named connection and open the. last named conmotion, and a. third position to connect the discharge and inlet portswith the low pressure reservoir for; preventing the. supplying of fluid pressure to either reservoir, and means responsive to variations in pressure in both reservoirs for moving said value to the fist named position when. the pressure: in. the low pressure reservoir exceeds a predetermined value and for permitting movement of said valve from the third named position to said second named position by the operation of said means when. the pressure in the high pressure reservoir drops below a predeterminedva-lne. i V

WILFRED A. E-ATON.

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