US2980073A - Fluid control means - Google Patents

Description

Apnl 18, 1961 D. J. ARBOGAST FLUID CONTROL MEANS Filed Nov. 9, 1959 FIG. 2

FIG.I

INVENT OR DUANE J. ARBOGAST FIG. 4

FIG. 3

Eta,

FIG. 5

United States Patent G F FLUID CONTROL MEANS Duane J. Arbogast, Shelby County, Tenn., assignor to Dover Corporation, Washington, D..

Filed Nov. 9, 1959, Ser. No. 851,888

15 Claims. (Cl. 121-464) This invention relates to improvements in constant flow valves, and in particular, to improvements in valves to be used in hydraulic elevator systems for maintaining a constant lowering speed of the elevator car regardless of load variations in the car.

Hydraulic elevators in their modern form are commonly equipped with a jack cylinder and an elevator car supporting plunger reciprocable therein. For raising the elevator car, hydraulic fluid is supplied under pressure to the jack cylinder by means of a pump, and for lowering the car, the hydraulic fluid, which is under pressure due to the supported weight of the plunger, the elevator car, and its load, is allowed to return from the jack cylinder to a reservoir through valve means. It is towards the improvement of said valve means and its relationship to the elevator system that the present invention is particularly directed. Other valve means known to me which perform the three functions of maintaining a constant lowering speed of the elevator car, reducing the volume of flow to a smaller amount for leveling of the elevator car, and closing the flow 01f altogether to hold the elevator in position, have involved at least two main valve elements. For example, in Patent No. 2,785,660, issued March 19, 1957, to Lawrence F. Jaseph, two valves were used, the control valve and the lowering valve 24. The present invention performs the above-mentioned three functions by a single main element or valve so that a compact valve means is provided which is simple in construction and economical to manufacture.

Thus, one of the objects of the present invention is to provide a compact valve having a single main element which is adapted to perform in a hydraulic elevator system the functions of maintaining a constant lowering speed of the elevator car regardless of load, reducing the volume of flow to a smaller amount for leveling of the elevator car, and closing the flow off altogether to hold the elevator in position.

A further object is to provide a valve adapted to receive fluid under pressure comprising means providing a discharge port, throttling means in said discharge port movable therein to various positions for controlling the discharge of fluid through said port, means providing a restricted orifice upstream of said discharge port to establish a pressure drop of the fiuidflowing through said orifice, and positioning means for moving said throttling means responsive to changes in said pressure drop to maintain the volumetric flow through said discharge port substantially constant regardless of pressure changes in the fluid flowing to said valve.

A further object is to provide means in such a valve to compensate for the variations in the distance that the elevator travels during stopping as the load varies.

A further object is to provide a constant flow valve which is simple in construction, economical to manufacture, and eflicient in operation.

A further object is, generally, to improve the design Patented Apr. 18, 1951 and construction of constant speed lowering means in an elevator system.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawing wherein:

Fig. 1 is a diagrammatic view of a hydraulic elevator system showing the principal components thereof, including the constant flow valve of the present invention,

Which is shown in section with certain parts being shown in elevation and parts being broken away for purposes of clarity.

Fig. 2 is an enlarged view of a fragmentary portion of the constant flow valve of Fig. 1, illustrating the pilot valve thereof in a raised position and with a part thereof being broken away for purposes of illustration.

Fig. 3 is a further enlarged sectional view taken as on the line IIIIII of Fig. 1.

Fig. 4 is a perspective view of the plug used in the constant flow valve for establishing a variable orifice. I

Fig. 5 is an enlarged sectional view of an alternate arrangement of a portion of the constant flow valve of Fig. 1.

Referring now to the drawings in which the various parts are indicated by numerals, the typical hydraulic elevator system shown in Fig; 1, in which the valve 11 of the present invention is-adapted to be used, includes a jack 13 having a plunger 15 reciprocally mounted in jack cylinder 17, which is adapted to be buried in the ground or otherwise fixedly supported. An elevator car 18 is supported'by plunger 15 adjacent the upper end thereof and is provided with the usual guideways, not shown. At the upper end of cylinder 17 is provided the usual guide 19 attached by bolts or the like to cylinder 17, and suitable resilient packing means, indicated as at.21, seals the sliding contact between plunger 15 and guide 19. In addition, a gland 23 adjustably compresses packing means 21 and is secured to guide 19 as by screws or the like. A fluid conduit 25 communicates at one end with the interior of jack cylinder 17 and is branched adjacent the opposite end with one branch extending to the inlet chamber 27 of valve 11. and the other branch 29 extending to a power unit 31, which includes a hydraulic fluid pump 33, preferably of the constant displacement type; a prime mover 35, as.an electric motor or the like; and a drive belt 37. Additionally, the hydraulic system includes an open reservoir 39 for hydraulic fluid, which is supplied to pump 33 through conduits 41 and 43, communicating the reservoir with the pump. Also, the outlet chamber 45 of valve 11 is communicated with conduits 41 and 43.

For raising car 18, hydraulic fluid is supplied under pressure to jack cylinder 17 by means of pump 33. A

1 check valve 47 is provided in the system in branch 29 From a consideration of the above general description of an elevator system, it will be understood that in prior elevator systems of this type, in which a conventional lowering valve was used in the system in place of valve 11, as the load increased in the elevator car, the input pressure to the lowering valve would increase, which, in turn, would cause an increase in the volumetric rate of flow of fluid through the lowering valve, and thus an increase in the lowering speed and stopping distance of the elevator car. The means by which the present invention overcomes these difficulties will be apparent from the following detailed description of valve 11 and its relationship to the elevator system.

Valve 11 includes a valve body 49, containing, in general, three cavities, i.e., inlet chamber 27, outlet chamber 45 and an intermediate chamber 51. Valve body 49 is preferably formed in two parts, i.e., a lower part 53 having a flange 54, and an upper part 55, having a flange 56, which flanges 54, 56 are removably secured together by bolts 59.

Inlet chamber 27 and intermediate chamber 51 are communicated by way of a variable restricted orifice 65, which preferably takes the form of a plug 67 rotatably mounted in an interrupted cylinder 69 provided in valve body 49 between inlet chamber 27 and intermediate chamber 51. Cylinder 69 extends through the valve body 49 at the near end thereof (i.e., the end nearest the viewer of Fig. 1). Plug 67 includes ends 7 1 connected by spaced arcuate sides 73, 74, between which fluid is adapted to flow. Side 73 subtends an angle large enough so that when plug 67 is rotated to its extreme closed position, as shown in dotted lines in Fig. 1, it will interrupt substantially all of the passage between chambers 27, 51, and the angle is small enough so that in' its most open position, which it will be understood is the position substantially 90 degrees from that shown by dotted lines in 1, it will cause negligible restriction in the passage between chambers 27, 51. Suitable means, not shown, is provided to clamp lug 67 when the correct position therefor has been found, which correct position will be understood more fully in the hereinafter described operation of the device. An annular groove 75 is provided in plug 67 adjacent the near end thereof (i.e., the end nearest the viewer of Figs. 1 and 4), in which groove is adapted to be received suitable sealing means to seal between the plug and the valve body 49. In addition, a suitable shaped boss 76 projects from the near end of plug 67 to permit the plug to be rotated when unclamped.

Valve body 49 includes a partition 77 which separates outlet chamber 45, which is on one side of the partition, from inlet chamber 27 and intermediate chamber 51, which are on the other side thereof. Partition 77 is provided with a cylindrical discharge port 79 therethrough adapted to permit flow of hydraulic fluid from intermediate chamber 51 to outlet chamber 45.

A substantially cylindrical throttling member 81 is closely and slidably mounted in discharge port 79. Throttling member 81 includes a substantially circular wall 33 and an annular side wall 85 integrally formed with circular wall 83 and slidably extending outwardly (to the left as viewed in Fig. 1) through discharge port 79 into outlet chamber 45. Side wall 85 adjacent its outer end is provided with spaced and substantially V- shaped notches 86 so that when the throttling member 81 is moved to the right, as viewed in Fig. l, the notches provide gradually increasing passage area to communicate intermediate chamber 51 with outlet chamber 45, and when the throttling member is moved to the left as viewed in thisfigure, the notches provide gradually decreasing passage area until the throttling member reaches its limit in its movement to the left, which limit is shown in Fig. l, and which closes off discharge port 79. A beveled lip portion 87 is provided on throttling member 81, which lip portion is integrally formed adjacent the outer periphery of circular wall 83 and extends therebeyond. A corresponding beveled seat 83 is provided in partition 77 adjacent discharge port 79 and on the side of the partition adjacent intermediate chamber 51 so that when throttling member 81 is seated, as shown in Fig. 1, there is no fluid escape through port 79 from intermediate chamber 51. Thus, the co-action of throttling member 81 and discharge port'79 provides a throttling valve 89, which is adapted to throttle the fluid flow from intermediate chamber 51 to outlet chamber 45.

Valve body 49 is provided with a first cylinder 91, which opens into outlet chamber 45 on the opposite side of the outlet chamber from discharge port 79. Cylinder 91 is preferably, though not necessarily, of the same diameter as discharge port 79 and is in spaced alignment therewith. A first piston member 93 is slidably mounted in first cylinder 91.

A second cylinder 95 is provided in valve 11, which cylinder opens into intermediate chamber 51 on the opposite side of the intermediate chamber from discharge port 79. Second cylinder 95 is preferably, though not necessarily, of the same diameter as discharge port 79 and is in spaced alignment therewith. Second cylinder 95 is formed in a closure cap 97 to permit removal of throttling member 81, which is larger than second cylinder 95 because of the beveled lip portion 87. Closure cap 97 comprises an end wall 99 and an annular Wall 101, which extends inwardly from end wall 99 into a bore 153 provided in valve body 49. Closure cap 97 additionally includes a flange 105, which provides the means by which the closure cap is secured to the valve body with bolts 197. A hollow second piston member 109 is slidably mounted in second cylinder 95.

A stem 111 is rigidly connected adjacent one end to first piston member 93 adjacent the central portion of the first piston member and is rigidly connected adjacent the opposite end to throttling member 81 adjacent the central portion of end wall 83. Likewise, a second stern 113 is rigidly connected to throttling member 81 adjacent the center portion of end wall 83 on the opposite side from stem 111. The opposite end of second stem 113 from end wall 53 is rigidly attached to second piston member 109 adjacent the central portion thereof. Thus, from the foregoing, it will be understood that a unitary piston assembly 115 is provided, which includes first piston member 93 at the left end thereof, throttling member 81 in the middle thereof and second piston member 109 at the right end thereof, all as viewed in Fig. 1. It will be noted from Fig. 1 that piston assembly 115 spans intermediate chamber 51 and outlet chamber 45.

A compression spring 117 bears against piston assembly 115 so that the piston assembly is biased by the spring to the right as viewed in Fig. 1. Compression spring 117 is preferably received in a socket 119 extending through first stem 111 and opening outwardly through first piston member 93. A passage 121, which principally is provided in valve body 49 and which includes an extension 123 through closure cap 97, communicates between inlet chamber 27 and second cylinder 95. An opening 125 is provided in annular wall 101 intermediate the ends thereof and communicates with outlet chamber 45 by the following path: A conduit 127, a solenoid valve 129, a needle valve 131, and a conduit 133. A pilot valve governs other passages, and is, itself, governed by a solenoid valve 137. Pilot valve 135 includes a valve body 138 which contains a larger cylinder 139 in which piston 141 is slidablyfitted and a smaller cylinder 143 in which spool 145 is slidably fitted. Piston 141 and spool 145 are integral with each other and move as a unit. The space 147 below piston 141 communicates by a conduit 149 through a needle valve 151 and a conduit 153 with intermediate chamber 51. A small opening 155 is provided through piston 141 to admit fluid restrictively to the chamber 157 above the piston. Chamber 157 connects by means of a conduit 159 to solenoid valve 137, which is drained to outlet chamber 45 through a conduit 161 communicating with conduit 133.

When spool 145 is in the downward position shown in Fig. 1, communication between the chamber 163, located behind first piston member 93, and outlet chamber 45 is established through the following path: A conduit 165, communicating chamber 163 with cylinder 143; the space in cylinder 143 surrounding the smaller portion 172 of spool 145; a conduit 171, communicating cylinder 143 with needle valve 173; a conduit 174, communicating needle valve 173 with cylinder 143 below spool 145; a conduit 175 which communicates cylinder 143 below spool 145 with conduit 133; and conduit 133.

An access plug 177 is threadedly engaged in a threaded bore 179 in the upper end of pilot valve body 138. A compression spring 181 is disposed between access plug 177 and piston 141 to urge the piston and spool 145 into the downward position shown in Fig. 1. When piston 141 and. spool 145 are caused to shift into the upward position shown in Fig. 2 by means that will be more fully understood in the hereinafter described operation of valve 11, chamber 163 communicates with intermediate chamber 51 by the following path: Conduit 165, the space in cylinder 143 surrounding portion 172, space 147, conduit 149, needle valve 151 and conduit 153.

Second piston member 109 has its right-hand edge 183 formed as an interrupted helix so that as the piston moves to the right, it is adapted to cut 011 the opening 125 at various points in the travel of the piston, depending on the rotational position thereof.

Second piston member 109 is adapted to be rotated and inadvertent rotation is adapted to be prevented by the following means: A central bore 185 is provided in second stem 113 and opens into the hollow interior of second piston member 109. A pair of longitudinally extending grooves 187 are provided in stem 113 on opposite sides of central bore 185. In grooves 187 are respectively received the opposite ends of a pin 189 that is fixedly carried by a guide rod 191, which extends through an aperture 193 provided centrally through end wall 99 with an enlarged portion 192 of the guide rod abutting the end wall and which guide rod is clamped in position by a nut 195 threadedly engaged on the threaded end portion 197 of the guide rod. It will be understood that by the foregoing described means second piston member 189 is adapted to reciprocate, but cannot rotate except when the adjustment is unclamped and turned to a new setting.

With solenoid valves 129 and 137 are de-energized, as is shown in Fig. 1, the chamber, 163 behind piston 93 is in communication with outlet chamber 45, as heretofore described, and is, therefore, not under pressure. Cylinder 95 is in communication through passage 121 with inlet chamber 27, and is, therefore, underfull pressure existing by virtue of the weight of elevator 18 supported on plunger 15. Consequently, the pressure existing ininlet chamber 27 and intermediate chamber 51 is exerted left ward (as viewed in Fig. 1) on piston assembly 115 to hold throttling member 81 firmly to its seat, not withstanding the bias of spring 117. Thus, there is no escape of hydraulic fluid from inlet chamber 27 and intermediate chamber 51 so that the elevator car 18 is held in its stopped position.

When lowering of the elevator 18 is desired, solenoid valve 137 is energized by suitable switches and electrical circuits not shown which will cause its needle 199 to lift, thereby establishing communication between chamber 157 and outlet chamber 45, by which means fluid is drained from chamber 157. Since the jack pressure is admitted through conduits 153 and 149 to space 147, piston 1 41 is raised carrying with it spool 145 to the position shown in termediate chamber 51 downstream of this restricted orifice, the pressuredifference will be evidenced at the two pistons 93 and 109'governing throttling valve 89, the right-hand one (piston 109) having the higher pressure applied thereto and the left-hand one (piston 93) having the lower pressure applied thereto. At a certain rate of flow, which is the desired rate for which the valve is adjusted, this difference in pressure will balance exactly the bias of spring 117, and in this position the valve will be an equilibrium and will tend neither to open nor to close. If anything occurs which tends to change the pressure in inlet chamber 27, as by the load being removed from elevator 18, the reduced pressure will tend to cause a reduced flow, but it will also reduce the difference in pressure between inlet chamber 27 and intermediate chamber 51, and thereby reduce the differential force acting leftward onpistoh assembly 115 so that the Piston assembly will tend to move to the right and increase the flow through throttling valve 89, tending to restore the original rate of flow. On the other hand, when the pressure in chamber 27 rises, the pressure drop through orifice 65 will increase, and thereby increase the differential force acting left-ward on piston assembly 115 so that the valve will tend to move to the left and decrease the flow through throttling valve 89, tending to restore the 7 original rate of flow.

When a reduced rate of flow is desired,- as for reducing the speed of elevator 18 when approaching a landing so that an'accurate stop can be made, solenoid 137 is deenergized to lower needle 199 and solenoid 129 is energized to raise the needle 263 thereof. Closing of solenoid valve 137 closes the escape for fluid from space 157; piston 141 thereupon moves downward under the urging of spring 181 with fluid from space 147 returning to space 157 through aperture 155. This causes spool 145 to close thesupply passage through conduit 149 to chamber 163, and to permit chamber 163 to drain to outlet chamber 4-5 through means heretofore mentioned. Since full line pressure from jack cylinder 17 is admitted to Fig. 2. The moving of spool 145 to the raised position causes chamber 163 to be placed in communication with inlet chamber 51 by means heretofore mentioned.

Thus, fluid under pressure is admitted to chamber 163 balancing the hydraulic forces applied to piston assembly 115. Spring 117 then causes piston assembly 115 to move to the right, as viewed in Fig. l, to open throttling valve 89 at a rate regulated by the setting of needle valve 151 through which fluid must pass to gain admission to chamber 163 as the valve opens. As throttling valve 89 opens, fluid flow commences between inlet chamber 27 and intermediate chamber 51, which flow passes through restricted orifice 65. As this flow becomes substantial, the pressure drop through orifice 65, i.e., the difference in pressure between chambers 27 and 51, becomes appreciable. Since passage 121 connects to inlet chamber 27 upstream of orifice 65 while conduit 153 connects to incylinder through passages heretofore pointed out, and chamber 163 is in communication with reservoir 39 through passages also heretofore pointed out, the full pressure is applied to piston assembly to close throttling valve 89 which it does at a rate determined by thesetting of needle valve 173. However, when the advancing piston 109 uncovers opening 125, an outlet is aiforded to the hydraulic fluid entering through passage 121, and this outlet is larger in area than that of passage 121, so that pressure in cylinder 95 is reduced to a low value. The piston assembly 115 is no longer able to overcome the bias of spring 117 and the piston assembly, therefore, comes to rest at a nearly closed position of throttling valve 89, permitting a greatly reduced flow of fluid from intermediate chamber 51 to outlet chamber 45. At this setting-of the valve 89, no regulation occurs, but the amount of opening is substantially fixed. However, the velocity of descent of elevator 18 may be made sufficiently small that minor variations at this speed will be unimportant.

To close valve 11 and stop elevator 18, both solenoid valves 129' and 137 are de-energized; pressure consequently acts on piston assembly 115 to push the piston assembly all the way to the left and close throttling valve 89 to cut off all flow.

Adjustments of valve 11 include plug 67, which is rotated to vary the orifice 65 between chambers 27 and 51 and thereby the flow required to position piston assembly 115 in equilibrium, and consequently adjusts the volume of flow; needle valve 151, which adjusts the rate of opening of throttling valve 89 to full speed; needle valve 131, which adjusts the rate of opening of throttling valve 89 to low speed when solenoid valve 129 alone is energized; guide rod 191, which is rotated to turn piston 109 to vary low speed flow; and needle valve 173, which adjusts the rate of closing of throttling valve 89.

Fig. shows an alternate means which may be used, if desired, in place of needle valve 173, heretofore described. This alternate means is designed to reduce variations in distance that elevator 18 travels during stopping as the load therein varies. The cause of the variations in distance traveled as the load varies, which the alternate means overcomes, is explained as follows: At high pressures in inlet chamber 27, piston assembly 115 assumes a position which is a relatively small distance from the closed position while with low pressures in the inlet chamber the piston assembly assumes a position which is a much greater distance from the closed position in order to achieve the same fluid flow. Also, during closure with a high pressure in inlet chamber 2 7, a large pressure differential is applied across piston assembly 115, tending to produce rapid motion in the closing direction, while with a smaller pressure in chamber 27, there is a smaller pressure difference applied to close throttling valve 89. Since with high pressure there is a short stroke to be accomplished and a high pressure to accelerate it, closure of throttling valve 89 is very rapid and the travel of elevator 18 during closure of the throttling valve is very short, while with a light load and a low pressure, travel of the piston member 115 is long and slow and consequently, elevator 18 moves through a substantially increased distance, rendering control of the motion difficult.

The only modification of valve 11 needed in using said alternate means is in the replacement of regulating needle valve 173 with the means shown in Fig. 5, with the same connections of the conduits to the remainder of the valve as those in the preferred embodiment beig used with the exception that an additional branch of conduit 153 is provided so that the conduit leads to the alternate means as shown in Fig. 5, in addition to the connection to needle valve 151. In the alternate means, conduit 171 now communicates with conduit 174 by a port 205, in which a needle 207 is positioned. Needle 207 is threaded into a piston 299 adapted to reciprocate in a cylinder 211, which is communicated adjacent its upper end to conduit 174 and is communicated adjacent its lower end with conduit 153. Piston 2% is provided with a resilient packing ring 213 which is retained by a nut 215 threadedly engaged on the lower end of needle 207 and which, likewise, secures needle 297 against creeping. Cylinder 211 is closed adjacent its outer end by a plug 217. A spring 219 biases piston 269 to its needle-open position, and this bias is opposed by the pressure from intermediate chamber 51 applied below piston 209 through conduit 153. Therefore, the higher the pressure in intermediate chamber 51, the more nearly port 295 is closed by needle 207, and conversely the lower the pressure in intermediate chamber 51, the more port 2% is opened by needle 207. The proper taper should be formed on needle 207 so that port 265 will be so restricted for each pressure that equal time will be required to close throttling valve 89, and stops taking equal distance and of equal comfort to passengers will result. It should be noted that taper of needle 207 must be correlated with the shape of the l-shaped notches 86 for equal stopping rates to be achieved when needle 207 is moved relative to piston 28% for adjustment of stopping rate.

From the foregoing description, it is apparent that the constant flow valve 11 of the present invention provides a simple, compact and efficient means for maintaining different lowering speeds constant at selected predetermined values regardless of load variations. Also, it is apparent that improved means is provided to compensate for variations in distance that the elevator travels during stopping as the load varies.

Although the invention has been described and illustrated with respect to a preferred embodiment thereof, it is to be understood that it is not to be so limited since changes and modifications may be made therein which are within the full intended scope of this invention as hereinafter claimed.

I claim:

1. In a hydraulic elevator control system having a jack cylinder and an elevator car supporting plunger reciprocable therein, means providing an inlet chamber and an intermediate chamber, a passage communicating said jack cylinder with said inlet chamber whereby said inlet chamber receives hydraulic fluid under pressure from said jack cylinder, means providing a restricted orifice communicating said inlet chamber with said intermediate chamber whereby said orifice permits flow of fluid from said inlet chamber into said intermediate chamber and causes a drop in fluid pressure therethrough so that the pressure in said intermediate chamber is lower than that in said inlet chamber by an amount depending upon the fluid flow through said orifice, means providing a discharge port for said intermediate chamber, throttling means in said discharge port movable therein to various positions for controlling the discharge of fluid from said intermediate chamber, postioning means connected to said throttling means for moving said throttling means in response to changes in said pressure drop through said orifice to maintain the volumetric flow through said discharge port substantially constant regardless of pressure changes in said inlet chamber.

2. In a hydraulic elevator control system having a jack cylinder and an elevator car supporting plunger reciprocable therein, means providing an inlet chamber and an intermediate chamber, a passage communicating said jack cylinder with said inlet chamber whereby said inlet chamber receives hydraulic fluid under pressure from said jack cylinder, means providing a restricted orifice communicating said inlet chamber with said intermediate chamber whereby said orifice permits flow of fluid from said inlet chamber into said intermediate chamber and cause a drop in fluid pressure therethrough so that the pressure in said intermediate chamber is lower than that in said inlet chamber by an amount depending upon the fluid flow through said orifice; a piston assembly including a throttling member, a first piston and a second piston; said throttling member being interconnected between said first piston and said second piston so that said first piston is positioned adjacent one end of said piston assembly and said second piston is positioned adjacent the opposite end thereof with said throttling member being between said first and second pistons, means providing a discharge port for said intermediate chamber, said throttling member being slidably received in said port, said throttling member being provided with notches in one end thereof, said throttling member being movable to various positions in said port to control the fluid discharge from said intermediate chamber, biasing means for urging said piston assembly in a direction towards opening of said port by said throttling member, means providing a first cylinder, said first piston being slidably received in said first cylinder to establish a first chamber behind said first piston remote from said throttling member, means providing a second cylinder, said second piston being slidably received in said second cylinder to establish a second chamber behind said second piston remote from said throttling member and said first chamber, first conduit means communicating fluid under pressure from said intermediate chamber to said first chamber for urging said piston assembly towards opening of said port by said throttling member, and second conduit means communicating fluid under pressure from said inlet chamber to said second chamber for urging said piston assembly towards closing of said port by said throttling member, the position of said piston assembly and the amount of opening of said port by said throttling member being determined by the difference in pressure between said inlet chamber and said intermediate chamber.

3. The structure according to claim 2 including means for interrupting the communication of fluid from said intermediate chamber to said' first chamber and for draining the fluid from said first chamber, said biasing means having a force less than the opposing force caused by the fluid pressure from said inlet chamber acting in said second chamber on said piston assembly, whereby said piston assembly is moved towards closure of said port by said throttling member when the communication of fluid from said intermediate chamber to said first chamber is interrupted and said first chamber is drained.

4. The structure according to claim 2 including a first passage means for draining fluid from said first chamber; valving means shiftable between first and second positions, when in said first position said valving means being effective to interrupt the flow of fluid through said first conduit means and to open said first passage means for fluid flow, and when in said second position said valving means being effective to open said first conduit means for fluid flow and to interrupt the flow of fluid through said first passage means; means providing a third cylinder, a third piston rigidly connected adjacent one side thereof to said valving means and slidably mounted in said third cylinder to divide said third cylinder into a first space on the side of said third piston adjacent said valving means and a second space on the side of said third piston remote from said valving means, said third piston being provided with a small opening therethrough restrictively communicating said first and second spaces, spring means for urging said third piston in a direction to carry said valving means towards said first position, means communicating fluid under pressure from said intermediate chamber to said first space, solenoid operated means for selectively draining and closing off the fluid flow from said second space to cause said third piston to selectively shift into said second position and said first position to control the fluid flow to and from said first chamber, thereby controlling the opening and closing of said discharge port by said throttling member.

5. The structure according to claim 2 including communication means communicating said second chamber with a low pressure region, said communication means having an effective area greater than that of said second conduit means and opening into said second chamber at a point along the line of movement of said second piston, and means for selectively opening andclosmg said communication means to control the position of said second piston and thereby the position of said throttling member.

6. The structure according toclaim 4 including communication means communicating said second chamber with a low pressure region, said communication means having an eiiective area greater than that of said second conduit means and opening intosaid second chamber at a point along the line of movement of said second piston, and means for selectively opening and closing said communication means to control the position of said second piston and thereby the position of said throttling member.

7. The structure according to claim 4 including needle valve means responsive to fluid pressure in said inlet of said port by said throttling member is substantially I 10 said passageway, means for delivering fluid under pressure to said passageway whereby fluid flows through said passageway and through said port, throttling means in said port movable therein to various positions for controlling the flow of fluid through said port, means providing a restricted orifice upstream of said port to establish a pressure drop of the fluid flowing through said orifice, and positioning means for moving said throttling means responsive to changes in said pressure drop to maintain the volumetric flow through said port substantially constant regardless of pressure changes in the fluid flowing to said valve.

10. A valve for maintaining a constant flow of fluid comprising a valve body; means in said valve body establishing an inlet chamber, an intermediate chamber, and an outlet chamber; means for delivering fluid under pressure to said inlet chamber, means providing a restricted orifice communicating said inlet chamber with said intermediate chamber whereby said orifice permits flow of fluid from said inlet chamber into said intermediate chamber and cause a drop in fluid pressure therethrough so that the pressure in said intermediate chamber is lower than that in said inlet chamber by an amount depending upon the fluid flow through said orifice, means providing a discharge port communicating said intermediate chamber with said outlet chamber, throttling means in said discharge port movable therein to various positions for controlling the discharge of fluid from said intermediate chamber, positioning means connected to said throttling means for moving said throttling means in response to changes in said pressure drop through said orifice to maintain the volumetric flow through said discharge port substantially constant regandless of pressure changes in said inlet chamber.

11.'A valve for maintaining a constant flow of fluid comprising a valve body; means in said valve body establishing an inlet chamber, an intermediate chambe and an outlet chamber; means for delivering fluid under pressure to said inlet chamber, means providing a restricted orifice communicating said inlet chamber with said intermediate chamber whereby'said orifice permits flow of fluid from said inlet chamber into said intermediate chamber and cause a drop in fluid pressure therethrough so that the pressure in said intermediate chamber is lower than that insaid inlet chamber by an amount depending upon the fluid flow through said orifice; a piston assembly including a throttling member, a first piston and a second piston; said throttling member being interconnected between said first piston and said second piston so that said first piston is positioned adjacent one end of said piston assembly and said second piston is positioned adjacent the opposite end' thereof with said throttling member being between said first and second pistons, means providing a discharge port communicating said intermediate chamber with said outlet chamber, said throttling member being slidably received in said port, said throttling member being provided with notches in one end thereof, said throttling member being movable to various positions in said port to control the fluid discharge from said intermediate chamber to said outlet chamber, biasing means for urging said piston assembly in a direction towards opening of said port by said throttling member, means providing a first cylinder, said first piston being slidably received in said first cylinder to establish a first chamber behind said first piston remote from said throttling member, means providing a second cylinder, said second piston being slidably received in said second cylinder to establish a second chamber behind said second piston remote from said throttling member and said first chamber, first conduit means communicating fluid under pressure from said intermediate chamber to said first chamber for urging said piston assembly towards opening of said port by said throttling member, and second conduit means communicating fluid under pressure from said inlet chamber to said second chamber for 11 urging said piston assembly towards closing of said port by said throttling member, the position of said piston assembly and the amount of opening of said port by said throttling member being determined by the difference in pressure between said inlet chamber and said intermediate chamber.

12. The structure according to claim 11 including means for interrupting the communication of fluid from said intermediate chamber to said first chamber and for draining the fluid from said first chamber, said biasing means having a force less than the opposing force caused by the fluid pressure from said inlet chamber acting in said second chamber on said piston assembly, whereby said piston assembly is moved towards closure of said port by said throttling member when the communication of fluid from said intermediate chamber to said first chamber is interrupted and said first chamber is drained.

13. The structure according to claim 11 including a first passage means for draining fluid from said first chamber; valving means shiftable between first and second positions, when in said first position said valving means being effective to interrupt the flow of fluid through said first conduit means and to open said first passage means for fluid flow, and when in said second position said valving means being effective to open said first conduit means for fluid and to interrupt the flow of fluid through said first passage means; means providing a third cylinder, a third piston rigidly connected adjacent one side thereof to said valving means and slidably mounted in said third cylinder to divide said third cylinder into a first space on the side of said third piston adjacent said valving means and a second space on the side of said third piston remote from said valving means, said third piston being provided with a small opening therethrough restrictively communicating said first and second spaces, spring means for urging said third piston in a direction to carry said valving means towards said first position, means communicating fluid. under pressure from said intermediate chamber to said first space, solenoid operated means for selectively draining and closing 01f the fluid flow from said second space to cause said third piston to selectively shift into said second position and said first position to control the fluid flow to and from said first chamber, thereby controlling the opening and closing of said discharge port by said throttling member.

14. The structure according to claim 11 including communication means communicating said second chamber with a low pressure region, said communication'means having an eflective area greater than that of said second conduit means and opening into said second chamber at a point along the line of movement of said second piston, and means for selectively opening and closing said communication means to control the position of said second piston and thereby the position of said throttling member.

15. The structure according to claim 13 including needle valve means responsive to fluid pressure in said inlet chamber for regulating the rate of fluid flow through said first passage means in accordance with the fluid pressure in said inlet chamber so that the rate of closing of said port by said throttling member is substantially constant regardless of the pressure in said inlet chamber.

References Cited in the file of this patent UNITED STATES PATENTS 2,785,660 Iaseph Mar. 19, 1957

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