US3020892A

US3020892A - Constant flow valve assembly

Info

Publication number: US3020892A
Authority: US
Inventors: Duane J Arbogast; Lawrence F Jaseph
Original assignee: Dover Corp
Current assignee: Dover Corp
Priority date: 1959-11-04
Filing date: 1959-11-04
Publication date: 1962-02-13
Anticipated expiration: 1979-02-13

Description

Feb. 13, 1962 D. J. ARBOGAST EI'AL 3,020,892

CONSTANT FLOW VALVE ASSEMBLY Filed Nov. 4. 1959 2 Sheets-Sheet 1 FIG. I

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i 2 i i A I E 5 1? mm wil m mum. Wm] I i i L. FIG. 4

INVENTORS LAWRENCE F. JASEPH DUANE J. ARBOGAST BY WKQ H ATTORNEY United States Patent 3,020,892 CONSTANT FLOW VALVE ASSEMBLY Duane J. Arbogast, Shelby County, and Lawrence F.

Jaseph, Memphis, Tenn., assignors to Dover Corporation, Washington, D.C.

Filed Nov. 4, 1959, Ser. No. 850,958 17 Claims. (Cl. 121-464) The present invention relates to a constant flow valve assembly, particularly adapted for use 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 hydraulic elevator system that the present invention is particularly directed. In the typical hydraulic elevator system of today, said valve means comprising an electrically controlled lowering valve, in which system the speed of the descent of the elevator car varies with the load therein, with heavier loads producing faster speeds through an increase in the volumetric rate of fluid flow from the jack cylinder through the lowering valve to the reservoir. In such a system, the speed of downward travel varies nearly as the square root of the load. Since the useful load on a passenger elevator may easily exceed the dead load, the maximum load speed will exceed the empty car speed by forty (40%) percent or more. This condition is aggravated in certain higher rise plunger hydraulic elevator installations where the pressure and power required is reduced by partially counterweighting the weight of the car and plunger, in which case, the ratio of load borne by the plunger with loaded car to that with empty car is increased, and corresponding lowering speeds may well vary by a factor exceeding two. An accompanying difficulty is encountered in that the distance traveled during stopping varies somewhat with speed, though this is partly overcome by the means disclosed in Patent No. 2,355,164, issued to Lawrence F. Jaseph on August 8, 1944.

In years past, the probem mentioned above, of the variation in speeds due to load variations was not quite so pronounced as it is at present, since the car speeds of hydraulic elevator systems were not nearly as fast as those of today. For example, in years past, elevator speeds of fifty (50) feet per minute were common, whereas, today, speeds of one hundred seventy-five (175) feet per minute are common. Thus, with a no-load speed of fifty (50) feet per minute, a forty (40%) percent increase in speed due to a full load would not be so noticeable since seventy (70) feet per minute would be maximum with a difference of only twenty (20) feet per minute between no load and full load speeds. In contrast to this, with a no-load speed of one hundred seventy-five (175) feet per minute, a forty (40%) percent increase in speed due to a full load would be quite objectionable since there would be a two hundred and forty-five (245) feet per minute maximum and a seventy (70) feet per minute difference.

In Patent No. 2,785,660, issued March 19, 1957, to Lawrence F. ,laseph, one means was disclosed for overcoming the afore-mentioned difficulties of varying speeds and varying stopping distance with variations in car loads.

ice

Also, in the co-pending application, Serial No. 817,358, filed June 1, 1959, by Lawrence F. .laseph, one arrangement of a valve assembly for overcoming the above-mentioned difliculties is disclosed. However, the present invention provides a compact and efficient valve assembly that is vastly improved in operation over that shown in said Patent No. 2,785,660 and said application, Serial No. 817,358. In the device of said application, when a large volume of fluid is passed therethrough, the greater part of the pressure drop occurs in the input throttling valve, designated at in said application; and the drop through the selectively controlled throttling valve, designated as at in said application, is, in fact, regulated to a fixed value. Under these conditions, pronounced turbulence and eddying occur in the fluid downstream of the input throttling valve, and the pressure obtained from a tap such as at 153 in said application is variable and uncertain. A sufficient length of straight pipe or a baffle between the said input throttling valve and said controlled throttling valve would steady this flow, but either of these would defeat the achieving of compactness. The pressure difference between

chambers

91 and 57 of said application is utilized to cause opening of said controlled throttling valve, and since this pressure difference is regulated to a relatively small value, it is often diflicult to get sufficiently rapid opening motion.

The device of the present invention overcomes both of the above-mentioned disadvantages in the device of said application by providing a unitary valve assembly in which the selectively controlled throttling valve is located in the assembly upstream of the regulator valve so that the turbulence caused by the regulator valve does not effect the controlled throttling valve and the con trolled throttling valve operates more smoothly than the device in said application. In the present invention rather than regulating the pressure in the intermediate chamber between the two valves to a substantially constant pressure as was the case in the device of said application, the regulator valve, which is located downstream of the con trolled throttling valve, regulates the pressure in the intermediate chamber to such a value that the pressure drop through the controlled throttling valve is substantially constant for any given opening of the controlled throttling valve. In other words, with any given opening of the controlled throttling valve, as the pressure in the input to the controlled throttling valve varies, the effective back pressure on the controlled throttling valve is varied by the regulator valve to give a constant drop through the controlled throttling valve, thereby producing a constant volumetric flow through the controlled throttling valve and the valve assembly as a whole.

One of the objects of the present invention is to provide a compact and smoothly operating valve assembly for controlling the lowering speed of elevators.

A further object is to provide a unitary lowering valve assembly including a selectively controlled throttling valve and a regulator valve so arranged that there is rapid and positive opening and closing motion of the selectively controlled throttling valve.

A further object is to provide an improved arrangement of the parts of such a valve assembly in which the regulator valve is Located downstream of the controlled valve so that turbulence caused by the regulator valve is not transmitted to the controlled valve, and a vastly improved valve is obtained.

A further object is to provide improved means for controlling the lowering speed of a plunger type hydraulic elevator or like hydraulic device so that the speed of descent thereof will be substantially constant regardless of normal load variations.

A further object is to provide means for assuring the distance traveled during the closing of the valve assembly will be uniform as the load varies.

A further object is to provide means for eliminating all leakage from the fluid passage connected to the elevator jack when the latter is stopped.

A further object is to provide a unitary compact valve assembly comprising a controlled valve means for selectively varying the effective size of an opening, means for introducing fluid to said opening at various pressures, and means for regulating the back pressure on said opening so that the drop in pressure through said opening is substantially constant for any given effective size of said opening whereby the volumetric flow through said opening is constant for any given effective size of said opening.

A further object is to accomplish the foregoing objects in a simple, economical and highly etficient manner.

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

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

FIG. 2 is a cross-sectional view of said valve assembly, on a larger scale than FIG. 1, and taken as on a vertical plane through the middle of the valve assembly with certain parts being shown in elevation and certain parts being broken away for purposes of clarity.

FIG. 3 is a fragmentary cross-sectional view of a modified arrangement of the adjusting means of the valve assembly.

FIG. 4 is a fragmentary cross-sectional view similar to FIG. 2, but showing an alternate embodiment of the lower part of the valve assembly.

Referring now to the drawings in which the various parts are indicated by numerals, the typical hydraulic elevator system, shown in FIG. 1, with which the valve assembly 11 of the present invention is adapted to be used, includes a jack 13, having a plunger 15 reciprocally mounted in a 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 or passage 27 extending to valve assembly 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 hydraulie system includes a reservoir 39 for hydraulic fluid, a conduit 41 leading from reservoir 39 to pump 33 and a passage 43 leading from valve assembly 11 to conduit 41. For raising car 18, hydraulic fluid is supplied under pressure to jack cylinder 17 by means of pump 33. A check valve 45 is provided in the system between branch 29 and pump 33 to prevent reverse flow through the pump. For lowering car 18, the hydraulic fluid, which is under pressure due to its supporting the weight of plunger 15, elevator car 18 and the load therein is allowed to return to reservoir 39 through the valve assembly 11 of the present invention.

From a consideration of the above general description of an elevator system, it will be understood that in car elevator systems of this type, in which a conventional lowering valve was used in the system in place of valve assembly 11, as the load increased in the elevator car, the instant pressure to the lowering valve would increase, which, in turn, would cause an increase in the Volumetric rate of flow of the 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 difl'iculties will be apparent from the following detailed description of the preferred embodiment of valve assembly 11 and its relationship to the elevator system.

Valve assembly 11 includes a hollow valve body 47, including a first partition 49 and a second partition 51 provided in the interior of the valve body to establish an inlet chamber 53, an intermediate chamber 55, and an outlet chamber 57. First partition 49 separates inlet chamber 53 and intermediate chamber 55, and also, for a portion, separates inlet chamber 53 and outlet chamber 57. Second partition 51 separates intermediate chamber 55 and outlet chamber 57. Inlet chamber 53 and outlet chamber 57 open downwardly through valve body 47 at inlet opening 59 and outlet opening 60, respectively.

Chambers

53, 57 are respectively in communication with

passages

27, 43 through

openings

59, 60 and through openings 61, 62, which latter openings are respectively provided at the ends of

passages

27, 43. Valve body 47 is positioned with opening 59 being in alignment with opening 61 and opening 60 being in alignment with opening 62, as best shown in FIG. 1, and is held in such a position by a flange 63 at the lower end of the valve body, which flange is secured by bolts 65 or the like to a corresponding flange 67 encompassing openings 61, 62. From the foregoing, it will be understood that inlet chamber 53 is substantially in free communication with the interior of jack cylinder 17 whereby the pressure in the inlet chamber is substantially the same as that in the jack cylinder. Also, outlet chamber 57 is in substantially free communication with the reservoir 39 through passage 43 and conduit 41.

First partition 49 is provided with a cylindrical opening 69 therethrough adapted to permit flow of hydraulic fluid from inlet chamber 53 to intermediate chamber 55.

A selectively controlled throttling valve 71 is provided in valve assembly 11. The controlled throttling valve 71 and its associated parts are preferably constructed similar to the lowering valve of Jaseph Patent No. 2,355,164, previously referred to. The following general description of valve 71 will suffice, since a more detailed description may be obtained by referring to said Patent No. 2,355,164. Valve 71 includes a throttling valve member 73 cooperating with opening 69, and includes a disc 75 and wings 77 extending from the disc, and which wings have shaped notches 79 therebetween. Disc 75 is provided with a beveled seat 81 fitted fluid tight to a corresponding seat at the end of opening 69. Wings 77 fit closely in opening 69 and notches 79 provide fluid passageways when valve member 73 moves to the right, as viewed in FIG. 2. A piston 83, which is concentric with valve member 73 and substantially greater in cross-sectional area than opening 69, is rigidly connected to disc 75 by a stem 85, and is slidably mounted in a cylinder 87 provided in valve body 47. Cylinder 87 extends through the wall of the valve body 47 where it is closed off by a cover 89 mounted on the valve body as by bolts 91. The right-hand edge of piston 83 is formed helically, and is also notched to receive a transverse bar 93, the center of which engages a slot in an adjusting screw 97 that is threaded into cover 89. A handle 99 is fixedly mounted on the end of screw 97 so that by turning the handle, adjusting screw 97 is turned to rotate piston 83. A spring 101 biases piston 83 to the left or closed position, as viewed in FIG. 2, and keeps bar 93 in slot 95. A passage 103 is communicated at one end to the interior of cylinder 87 through a hole in the wall of the cylinder, which hole is so positioned that it will be covered or cut off by piston 83 after a partial right-ward motion thereof. Thus, the cut-off point of passage 103 may be adjusted by rotating piston 83, as above described to cause the helical edge of the piston to cut off the passage at varying points in the travel of the piston.

The chamber 105 established in cylinder 87 by pston 83 is connected to inlet chamber 53 by a conduit 107, an adjustable restriction valve 109, and a conduit 11 1. Chamber 105 may also be put in communication w th intermediate chamber 55 through an adjustable restriction valve 113, a magnetic valve 115 and a conduit 117. If des'red, rather than being connected into intermedi- .ate chamber 55 as shown in FIG. 2, conduit 117 may alternately be connected to outlet chamber 57 as shown in FIG. 4, so that the full pressure differential between inlet chamber 53 and outlet chamber 57 may be utilized in the operation of control throttling valve 71 to obta n a more rapid opening of valve 71. Another path lS provided from chamber 105 to intermediate chamber 55 through passage 103, a magnetic valve 119 and conduit 117.

Valves

109 and 113, respectively, includes screw needles 121 and 123 for varying the restrictions of the valves. When

magnetic valves

115 and 119 are de-energized, their

needles

125, 127 close fluid tight and there is no path of escape for fluid from chamber 105 to intermediate chamber 55. Thus, piston 83 and valve member 73 are held firmly in the closed posTtion, both by the bias of spring 101 and by the fluid pressure existing in inlet chamber 53, which is communicated to chamber 105 through the path above described.

Second partition 51 is provided with cylindrical dscharge port 129 therethrough adapted to permit the flow of hydraulic fluid from intermediate chamber 55 to outlet chamber 57. A cylindrical throttling member 131 is closely and sldably mounted in discharge port 129. Throttling member 131 includes a substantially circular inner end wall 133 and an annular side wall 135 integrally formed with circular wall 133 adjacent the periphery thereof and slidably extending outwardly (to the left as viewed in FIG. 2) through discharge port 129 into outlet chamber 57. The cylindrical side-wall 135 at its outer end 137 is provided with spaced and substantially V-shaped notches 139 so that when the throttling member 131 is moved to the right, as viewed in FIG. 2, the notches provide gradually increasing passage area to communicate intermediate chamber 55 with outlet chamber 57 and when the throttling member is moved to the left as viewed in this figure, the notches provide gradually decreas ng passage area until the throttling member reaches its limit in its movement to the left, which limit is shown in FIG. 2 and which substantially closes off discharge port 129. Thus, the co-action of throttling member 131 and discharge port 129 provides a regulator or throttling valve 141, which is adapted to throttle the fluid flow from intermediate chamber 55 to outlet chamber 57.

Valve body 47 is provided with a cylinder 143, which opens into outlet chamber 57 on the opposite side of the outlet chamber from discharge port 129. Cylinder 143 is preferably, though not necessarily, of the same diameter as discharge port 129 and is in spaced alignment therewith. A first piston member 145 is slidably mounted in cylinder 143.

A cap 147 is secured to valve body 47 as by bolts 149 and encloses the outer end of cylinder 143 to establish a head chamber 151, which includes the interior of cap 147, an annular cut-out portion 153 and the part of cylinder 143 exposed by piston member 145.

First part'tion 49 is provided with cylindrical bore 155. For manufacturing considerations, bore 155 is preferably, though not necessarily, of the same diameter as discharge port 129 and cylinder 143, and in addition, is in alignment wIth discharge port 129 and cylinder 143 on the opposite side of the discharge port from the cylinder. A second piston member 157 is closely and slidably fitted in bore 155. Second piston member 157 is provided at the end adjacent inlet chamber 53 with a beveled portion 159 to mate with corresponding beveled 6 seat 161 provided in first partition 49. Beveled seat 161 and beveled portion 159 are ground to fit fluid tight so that when second piston member 157 is seated, as shown in FIG. 2, there is no fluid escape through bore from inlet chamber 53.

A stem 163 is rigidly connected adjacent one end to second piston member 157 centrally thereof and is rigidly connected adjacent the opposite end to throttling member 131 adjacent the central portion of c'rcular wall 133. Likewise, a second stem 165 is rigidly connected to throttling member 131 adjacent the center portion of circular wall 133 and on the opposite side from stem 163. The opposite end of second stern 165 from circular wall 133 is rigidly attached to first piston member 145 adjacent the central portion thereof. Thus. from the foregoing. it will be understood that a unitary piston assembly 167 is provided, which includes first piston member 145 at the left end thereof, throttling member 131 in the middle thereof, and second piston member 157 at the right end thereof, all as viewed in FIG. 2. It will be noted in FIG. 2 that piston assembly 167 spans intermediate chamber 55 and outlet chamber 57. Also, it will be noted that throttling member 131 and second piston member 157 are so spaced that when the second piston member is seated, then discharge opening 129 is substantially closed by throttling member 131.

Head chamber 151 is in communication with intermediate chamber 55, preferably, through a conduit 168 provided in valve body 47 so that the pressure in head chamber 151 is substantially the same as that in intermediate chamber 55. If desired, the head chamber 151 may be communicated with intermediate chamber 55 through other means, as for example, a bore through stems 163 and 165, without departing from the spirit and scope of the present invention.

An access opening 169 is provided in valve body 47 opposite bore 155 to provide means for installing and replacing piston assembly 167. A cover plate 171 is provided for opening 169 and is removably secured to valve body 47 by means of bolts 173.

A compression spring 175 bears against first piston member 145 so that piston assembly 167 is biased by the spring to the right as viewed in FIG. 2. A sto 176 is provided on the interior of cover plate 171 and extends towards piston assembly 167 to limit movement thereof to the right. The outer end of first piston member 145 is preferably cupped as at 177 to receive spring 175. The opposite end of spring 175 is seated on shims 179, which, in turn, are seated on cap 147.

From the foregoing, it will be understood that the opposing forces acting on piston assembly 167 to control the amount of opening or closing of throttling valve 141 are as follows:

(1) The opening forces tending to move piston assembly 167 to the right, as viewed in FIG. 2, to unseat second piston member 157 and open throttling valve 141, which opening forces include spring 175 and the force of the fluid pressure in head chamber 151 acting on the first piston member 145.

(2) The closing forces tending to move piston assembly 167 to the left, as viewed in FIG. 2, to seat second piston member 157 and close throttling valve 141, which closing forces include the force of the fluid pressure in inlet chamber 53 exerted on second piston member 157 on an effective area thereof, which effective area is equal to the area of bore 155. As will be understood more fully in the hereinafter described operation of valve assembly 11, the pressure in the intermediate chamber 55 and thus, in head chamber 151 is less than the pressure in inlet chamber 53, so that, in effect, the two opposing forces are provided by (1) spring 175 and (2) a net force which equals the heretofore-mentioned force of the fluid pressure in inlet chamber 53 exerted on second piston memher 157 minus the heretofore-mentioned force of the fluid pressure in head chamber 151 acting on the first piston member 145.

Piston assembly 167 will remain in the closed position shown in FIG. 2 as long as controlled throttling valve 71 remains closed which is the condition that exists when the elevator car 18 is at a stop. The aforementioned fact that piston assembly 167 will remain in the closed position is so for the following reasons:

There is no escape for fluid from inlet chamber 53 because valve 71 is closed and the full pressure in inlet chamber 53 is exerted on second piston member 157. When said full pressure is exerted on second piston member 157, the heretofore mentioned net force acting on piston assembly 167 is greater than the force of spring 175 and piston assembly 167 will remain in said closed position. The spring tension of spring 175 should be so chosen that it exerts at all times a smaller force than said net force acting on piston assembly 167, due to an unloaded elevator car.

To lower elevator car 18, magnetic valve 115 is energized by suitable switches and electrical circuits, not shown. This will cause the pressure in chamber 105 to be reduced since fluid escapes from the chamber through conduit 117 into the lower pressure region in intermediate chamber 55 at a greater rate than the fluid enters chamber 105 through conduit 111. It will be understood that the fluid pressure in intermediate chamber 55 is lower than that in inlet chamber 53, since there is some leakage into outlet chamber 57 from intermediate chamber 55 past piston 145 and past throttling member 131. Needle 123 is adjusted to provide about twice the opening afforded by needle 121. As a result, the pressure in inlet chember 53 acting to the right on piston 83, as viewed in FIG. 2, is greater than the sum of the pressures acting to the left on the opposite side of the piston. Piston 83, therefore, moves to the right to open valve 71 and permit fluid to discharge through opening 69. This causes the pressure in intermediate chamber 55, and thus, the pressure in head chamber 151, to rise and the pressure in inlet chamber 53 to drop until the heretoforementioned net force exerted on piston assembly 167 is unable to oppose the bias of spring 175, whereupon piston assembly 167 will move to the right, as viewed in H6. 2, gradually moving notches 139 into intermediate chamber 55, thereby admitting corresponding fluid flow to outlet chamber 57 from intermediate chamber 55. It should be noted that the piston assembly 167 will actually begin its initial movement with the small flow through conduit 117, and then continue opening as above described.

When the heretofore-mentioned net force is such as to balance the bias of spring 175, piston assembly 167 will stop moving. As valve 71 opens wider and wider, increasing the flow from inlet chamber 53 to intermediate chamber 55, the heretofore mentioned net force on piston assembly 167 will tend to remain slightly less than enough to balance spring 175 which will cause piston assembly 167 to follow the movements of valve 71 and open throttling valve 141 progressively wider. When valve 71 reaches its limit of opening, which occurs when piston 83 abuts screw 97, the tendency for said net force to drop ceases and piston assembly 167 likewise ceases to move.

It will be understood that with a given opening of valve 71, as for example, the fully opened position above-described, the pressure drop through valve 71 will remain substantially constant regardless of the pressure variation in inlet chamber 53. Thus, with a heavier load in elevator car 18, which produces a greater pressure in inlet chamber 53, piston assembly 167 will move to the left as viewed in FIG. 2, to throttle down the fluid flow and increase the pressure in intermediate chamber 55 so that the pressure drop through throttling valve 71 will remain constant; and with a lighter load, piston assembly 167 will move to the right, as viewed in this figure, to increase the fluid flow to drop the pressure in intermediate chamber 55 so that the pressure drop through valve 71 is likewise regulated to a constant value. Since, with any given opening of valve 71, the pressure drop through throttling valve 71 remains substantially constant, the volumetric flow through valve assembly 11. will remain substantially constant and, therefore, cause a substantially constant lowering speed of car 18 with any given opening of valve 71.

When elevator car 18, in its lowering motion, approaches a landing at which stopping is desired, electrical circuits, not shown, are switched, as by switches, not shown, located in the hoistway and engaged by elevator car 18, to de-energize magnetic valve and simultaneously energize magnetic valve 119. Since the orifice of passage 103 into cylinder 87 is, at this time, covered by piston 83, there will be no escape for fluid from chamber 105, so pressure therein rises nearly to equal that in inlet chamber 53, and piston 83 with valve member 73 moves to the left, as viewed in FIG. 2, at a rate determined by the setting of needle 121. As valve 71 closes and restricts the flow through opening 69, the heretofore-mentioned net force acting against spring tends to rise, causing piston assembly 167 to move to the left, as viewed in FIG. 2, restricting the fluid flow through discharge port 129.

When piston 83 travels far enough to the left to uncover passage 103, egress is afforded for fluid entering chamber 105 through conduit 111, and closing motion of valve member 73 is interrupted. The elevator will now be descending at leveling speed, typically about one-fifth (Vs) of normal lowering speed. This leveling speed, for the same reasons heretofore-described for the faster lowering speed, will remain constant regardless of load changes, since, with a heavier load, throttling valve 141 will move toward closure to restrict the necessary fluid to maintain the pressure drop through valve 71 substantially constant.

The next step in the operation after the levelling speed is maintained, occurs when magnetic valve 119 is de-energized, which causes the pressure in chamber 105 to build up and the valve 71 to close which, in turn, causes throttling valve 141 to close, and consequently, all flow of fluid through valve assembly 11 is stopped, which stops the elevator car. As long as controlled valve 71 remains closed, car 18 will remain completely stationary since there is no escape of fluid from inlet chamber 53, as heretofore described, and consequently, there is no fluid flow through valve assembly 11.

To adjust the closing rate of the selectively controlled valve 71, the needle 121 is adjusted to the desired setting. However, this causes the fiow through valve 113, which is the adjustment for the opening rate of valve 71, to vary inversely as the flow thorugh valve 109 is changed, thereby necessitating a change in the setting of valve 113 every time valve 109 is changed. If it is desired to eliminate this condition, the valve assembly 11 is modified so that the opening adjustment is provided for valve 141 and eliminated on valve 71. Thus, restriction valve 113 is eliminated and an adjustable restriction valve 182 is provided in the conduit 168 between intermediate chamber 55 and head chamber 151. This modified construction is shown in FIG. 3; and, as will be apparent from this figure, valve 182 restricts the flow of fluid when it flows in a direction from intermediate chamber 55 toward head chamber 151, thereby controlling the rate of opening of throttling valve 141. In addition, in passage 168, a ball check valve 183 is provided to permit fluid to bypass valve 182 when the fluid flows in a direction from head chamber 151 towards intermediate chamber 55, thereby permitting free flow of fluid during closing of valve 141, and not affecting the closing thereof. From the foregoing, it will be understood that the closing adjustment is independent of the opening adjustment and one will not affect the other.

Referring now to the alternate embodiment of the valve assembly which is shown in FIG. 4, only the lower part of the modified valve assembly is shown since the upper part thereof is identical with the upper part of the preferred embodiment. The principal difference between the two embodiments is in the relationship of the compression spring and the dire::tion of the flow of the fluid through the discharge port. The other differences between the preferred and alternate embodiments will be more apparent from the description to follow of the alternate embodiment. The modified valve assembly of the alternate embodiment includes a throttling valve 184 comprising a throttling member 185, similar in construction to throttling member 131, cooperating with a discharge port 187. However, as will be noted in FIG. 4, the spaced notches 189 of throttling member 185 extend into intermediate chamber 55 rather than into the outlet chamber 57 as in the preferred form.

A cylinder 191 is provided in valve body 47 adjacent first partition 49. Cylinder 191 is spaced from discharge port 187 and in alignment therewith. A first piston member 193 is slidably mounted in cylinder 191 and a second piston member 195 is rigidly joined to first piston memher 193 and slidably received in a bore 197. Second piston member 195 corresponds to second piston member 157 in the preferred form, and it has the same function and substantially the same structure with the exception that second piston member 195 and bore 197 are smaller in diameter than first piston member 193 and throttling member 185. A stem 199 rigidly interconnects throttling member 185 and first piston member 193 so that a unitary piston assembly 201 is provided. A compression spring 202 corresponding to compression spring 175 urges piston assembly 201 towards opening of throttling valve 184,

It will be understood that the size of the second piston member 195 in the alternate embodiment may be made larger as in the preferred embodiment, or the second piston member 157 in the preferred embodiment may be smaller as in the alternate embodiment, or the second piston members may be other sizes than those shown without departing from the spirit and scope of the present invention, but it should be noted that the size of the compression springs should be changed to compensate for the changed area of the second piston member.

A chamber 203, which includes the space in cylinder 191 surrounding second piston member 195 and exposed by first piston member 193, is in communication with intermediate chamber 55 through a conduit 204.

From the foregoing, it will be understood that the opposing forces acting on piston assembly 201 to control the amount of opening or closing of throttling valve 184 are as follows:

(1) A first force is provided by the pressure in inlet chamber 53 acting on second piston member 195 tending to close throttling valve 184.

(2) A second force provided by the pressure in intermediate chamber 55 acting on throttling member 185 tending to open throttling valve 184.

(3) A third force tending to close throttling valve 184 and provided by the pressure in chamber 203 acting on the net area 205 of first piston member 193, which net area is equal to the cross-sectional area of first piston member 193 minus the cross-sectional area of second piston member 195.

The combined effect of said first force and said third force is greater than said second force whereby the net effect of the hydraulic fluid on piston assembly 201 is a net force equal to the combined first and third forces minus said second force which tends to carry piston assembly 201 towards closure of throttling valve 184. The compression spring 202 opposes said net force to cause operation of the valve assembly in a similar manner as that heretofore described for the operation of the principal embodiment.

It will be apparent from a comparison of the preferred and alternate embodiments that the fluid flow through throttling valve 141 is in the opposite direction to the thrust of compression spring 175, whereas the fluid flow through throttling valve 184 is in the same direction as the thrust of compression spring 202. It is preferable to have the fluid flow in the opposite direction to the thrust of the compression spring as in the preferred embodiment for the following reasons:

Springs and 202 will vary in force exerted as they are compressed or allowed to expand. Thus, as

springs

175 and 202 are compressed by

piston assemblies

167 and 201 respectively, the forces exerted by the springs increase somewhat; and as the springs expand, the force exerted by the springs decrease somewhat. This is an undesirable condition, since it will cause somewhat of a variation in the pressure in intermediate chamber 55 in the two embodiments for a given flow-rate through

discharge ports

129, 187. The impact of fluid is greater when high pressure fluid passes through a small opening than when the same quantity of low pressure fluid passes through a larger opening. The fluid flow through discharge opening 129 will strike portions of the piston assembly 167 in the path of the fluid flow, as for example, the area 207 on the end of first piston member 145, and the fluid through discharge port 187 will strike the area 209 on first piston member 193. In the preferred embodiment the effect of this fluid impact will be in the proper direction to compensate for the greater force exerted by spring 175 when it is compressed more. Thus, when the opening of throttling valve 141 is small as occurs with a high pressure in intermediate chamber 55, the impact on area 207 will be greater which will compensate for the greater force exerted by spring 175, and when the opening of throttling valve 141 is greater, which occurs with a lower fluid pressure in intermediate chamber 55, less force is exerted by the fluid on area 207, which is offset by the smaller force exerted by the spring 175. In the alternate embodiment, it will be apparent that this effect of the fluid force on area 209 will not compensate for the differences in spring tension, but instead is additive.

From the foregoing description, it is apparent that the valve assembly 11 of the present invention and the alternate embodiment thereof provide means for maintaining different lowering speeds constant at selected predetermined values which depend upon the opening of controlled valve 71, and which lowering speeds remain substantially constant regardless of load variations whereby closing time of the valve assembly and, therefore, distance traveled during such time are, likewise, independent of load. In addition, it is apparent that a compact valve assembly is provided in which the components operate smoothly without any adverse effects from turbulence.

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.

We claim:

1. In a hydraulic elevator control system having a jack cylinder and an elevator car supporting plunger reciprocable therein, means establishing a passageway including an opening therein, conduit means communicating said jack cylinder with said passageway whereby during descent of said elevator car supporting plunger hydraulic fluid is adapted to flow from said jack cylinder through said passageway and through said opening, controlled valve means for selectively varying the effective size of said opening, regulator valve means in said passageway downstream of said opening for changing the fluid back pressure on said opening in accordance with changes in the fluid pressure upstream of said opening so that the pressure drop through said opening is substantially constant for any given effective size of said opening, whereby the volumetric fluid flow through said opening and said passageway is substantially constant to maintain the lowering speed of said elevator car supporting plunger substantially constant for any selected size of said opening.

2. The structure according to claim 1 including means associated with said controlled valve means maintaining substantially uniform acceleration and retardation of the enlarging and closing of said opening from one effective size to another regardless of the fluid pressure upstream of said opening whereby the acceleration and retardation of said elevator car is maintained substantially uniform regardless of load variations therein.

3. In a hydraulic elevator control system having a jack cylinder and an elevator car supporting plunger reciprocable therein, means establishing a passageway including an opening therein and including a port therein, conduit means communicating said jack cylinder with said passageway whereby during descent of said elevator car supporting plunger hydraulic fluid is adapted to flow from said jack cylinder through said passageway and through said opening and said port, said port being located in said passageway downstream of said opening, controlled valve means for selectively varying the efiective size of said opening, throttling means in said port movable therein to various positions for controlling the rate of flow through said port, and positioning means connected to said throttling means and sensitive to fluid pressure upstream of said opening for changing the throttling eflect of said throttling means in accordance with changes in fluid pressure upstream of said opening so that the pressure drop through said opening is substantially constant for any selected size of said opening regardless of changes in fluid pressure upstream of said opening, whereby the volumetric fluid flow through said opening and said passageway is substantially constant to maintain the lower ing speed of said elevator car supporting plunger substantially constant for any selected size of said opening.

4. In a hydraulic elevator control system having a jack cylinder and an elevator car supporting plunger reciprocable therein, means establishing a passageway including an opening therein and including a port therein, conduit means communicating said jack cylinder with said passageway whereby during descent of said elevator car supporting plunger hydraulic fluid is adapted to flow from said jack cylinder through said passageway and through said opening and said port, said port being located in said passageway downstream of said opening, controlled valve means for selectively varying the effective size of said opening, throttling means in said port movable therein to various positions for controlling the rate of flow through said port, and positioning means connected to said throttling means, said positioning means including means for biasing said throttling means towards opening of said port, and means communicating fluid under pressure from upstream of said opening to said positioning means and acting in opposition to said biasing means for moving said throttling means towards closing of said port to maintain the pressure drop through said opening and the volumetric flow through said passageway substantially constant regardless of changes in the fluid pressure upstream of said opening.

5. 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, conduit means communicating said jack cylinder with said inlet chamber whereby said inlet chamber is adapted to receive hydraulic fluid under pressure from said jack cylinder, means providing an opening communicating said inlet chamber with said intermediate chamber whereby said opening is adapted to permit flow of fluid from said inlet chamber into said intermediate chamber, means for selectively varying the effective size of said opening, 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, and movable positioning means connected to said throttling means, said positioning means including spring means for biasing said throttling means towards opening of said port, and means communicating fluid under pressure from said inlet chamber to said positioning means and acting in opposition to said biasing means for moving said throttling means towards closing of said port to maintain the pressure drop through said opening substantially constant and, therefore, the lowering speed of said elevator car supporting plunger substantially constant for any selected size of said opening.

6. The structure according to claim 5, in which said positioning means includes an area thereon disposed in the stream of hydraulic fluid flow through said port and arranged so that the increasing tension of said spring means acting on said positioning means as it is moved in a direction causing closing of said port by said throttling means is compensated for by the increasing opposite force of the stream of hydraulic fluid impinging on said area disposed in the stream of hydraulic fluid flow.

7. The structure according to claim 5 in which said means for selectively varying the effective size of said opening includes means maintaining substantially uniform acceleration and retardation of the enlarging and closing of said opening from one eflective size to another regardless of the fluid pressure upstream of said opening whereby the acceleration and retardation of said elevator car is maintained substantially uniform regardless of load variations therein.

8. A valve assembly for maintaining a constant flow of fluid for any given setting of the valve comprising a valve body, means in said valve body establishing a passageway therethrough including an opening in said passageway, means for delivering fluid under pressure to said passageway whereby fluid is adapted to flow through said passageway and through said opening, con trolled valve means for selectively varying the effective size of said opening, said controlled valve means in addition being operable to close off completely said opening to stop the flow therethrough, said controlled valve including means for maintaining the retardation of flow through said opening during the closing thereof substantially constant regardless of pressure changes in said passageway upstream of said opening, regulator valve means in said passageway downstream of said opening for changing the fluid back pressure on said opening in accordance with changes in the fluid pressure upstream of said opening so that the pressure drop through said opening is substantially constant for any given effective size of said opening, whereby the volumetric fluid flow through said opening and said passageway is substantially constant for any given effective size of said opening.

9. A valve comprising a valve body, means in said valve body establishing a passageway therethrough including an opening therein and including a port therein, means for delivering fluid under pressure to said passageway whereby fluid is adapted to flow through said passageway and through said opening and said port, means in said opening to vary selectively the effective size of said opening between various positions of opening down to a condition in which the flow is completely cut oil, means operably coupled to said means in said opening for main taining the retardation of flow through said opening during the closing thereof substantially constant regardless of pressure changes in said passageway upstream of said opening, said port being located in said passageway downstream of said opening, throttling means in said port movable therein to various positions for controlling the rate of flow through said. port, and positioning means connected to said throttling means and sensitive to fluid pressure upstream of said opening for changing the throttling effect of said throttling means in accordance with changes in fluid pressure upstream of said opening so that the pressure drop through said opening is substantially constant, whereby the volumetric fluid flow through said valve is substantially constant.

10. A unitary valve for maintaining a constant flow of fluid for any given setting of the valve comprising a hollow valve body, means in said valve body establishing an inlet chamber, an intermediate chamber, and an outlet chamber; means for d: livering fluid under pressure to said inlet chamber, means forming an opening between said inlet chamber and said intermediate chamber to permit flow of fluid from said inlet chamber to said intermediate chamber, means associated with said opening to provide first valve means for valving the flow of fluid through said opening, control means for controlling the amount of opening of said first valve means, said first valve means being selectively controlled by said control means between various positions of opening down to a position in which the flow is completely cut oil, means forming a discharge port between said intermediate chamber and said outlet chamber to permit flow of fluid from said intermediate chamber to said outlet chamber, said valve body being provided with a cylinder, means forming a bore between said inlet chamber and said intermediate chamber, means establishing an additional chamber in communication with one end of said cylinder, said cylinder being in communication adjacent the opposite end from said additional chamber with said outlet chamber; said port, said bore and said cylinder being spaced apart and being in axial alignment; a unitary piston assembly including a throttling member intermediate the ends thereof, said unitary piston assembly being slidably received in said bore and said cylinder adjacent opposite ends thereof with said throttling member being slidably received in said port, said unitary piston assembly being movable as a whole to carry said throttling member to various positions in said port to control the fluid flow from said intermediate chamber into said outlet chamber, said assembly having an effective area adjacent one end thereof exposed to fluid under pressure in said inlet chamber to provide a first force tending to carry said assembly in one direction towards closure of said port by said throttling member, means communicating the fluid pressure in said intermediate chamber with said additional chamber and with portions of said piston assembly for establishing a net force acting on said piston assembly to urge said piston assembly in a direction towards opening of said port by said throttling member, compression spring means biasing said assembly in a direction opposite from said net force so that with any given setting of said first valve means and with changes in the fluid pressure in said inlet chamber said assembly is moved to maintain the pressure drop across said opening substantially constant, thereby maintaining the flow of fluid through said valve as a whole substantially constant.

11. A unitary valve for maintaining a constant flow of fluid for any given setting of the valve comprising a ho1 low 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 forming an opening between said inlet chamber and said intermediate chamber to permit flow of fluid from said inlet chamber to said intermediate chamber, means associated with said opening to provide first valve means for valving the flow of fluid through said opening, control means for controlling the amount of opening of said first valve means, said first valve means being selectively controlled by said control means between various positions of opening down to a position in which the flow is completely out off, means forming a discharge port between said intermediate chamber and said outlet chamber to permit flow of fluid from said intermediate chamber to said outlet chamber, said valve body being provided with a cylinder, means forming a bore between said inlet chamber and said intermediate chamber and forming a beveled seat surrounding said bore on the side of said partition adjacent said inlet chamber, said cylinder being in communication adjacent one end with said outlet chamber; said port, said bore and said cylinder being spaced apart and being in axial alignment; a unitary piston assembly including a throttling member intermediate the ends thereof, said unitary piston assembly being slidably received in said bore and said cylinder adjacent opposite ends thereof with said throttling member being slidably received in said port, said unitary piston assembly being movable as a whole to carry said throttling member to various positions in said port to control the fluid flow from said intermediate chamber into said outlet chamber, said unitary piston assembly being provided with a seating portion adapted to cooperate with said beveled seat to substantially close off any fluid leakage through said bore when said seating portion is seated thereagainst; said assembly having an effective area adjacent one end thereof exposed to fluid under pressure in said inlet chamber to provide a first force tending to carry said assembly in one direction towards closure of said port by said throttling member and tending to carry said seating portion towards seating, said assembly having an opposing area on said throttling member opposite said effective area and exposed to fluid under pressure in said intermediate chamber to provide a second force urging said assembly in a direction to carry said throttling member towards opening, means communicating fluid pressure from said intermediate chamber to a net area on said first piston opposite said opposing area to provide a third force tending to carry said assembly in a direction towards closure of said port by said throttling member, the combined effect of said first force and said third force being greater than said second force whereby the net effect on said assembly is a net force equal to the combined first and third forces minus said second force which tends to carry said assembly towards closure of said port by said throttling member, compression spring means biasing said assembly in a direction opposite from said net force so that with any given setting of said first valve means and with changes in the fluid pressure in said inlet chamber said assembly is moved to maintain the pressure drop across said opening substantially constant, thereby maintaining the flow of fluid through said valve as a whole substantially constant.

12. A unitary valve for maintaining a constant flow of fluid for any given setting of the valve comprising a hollow 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 forming an opening between said inlet chamber and said intermediate chamber to permit flow of fluid from said inlet chamber to said intermediate chamber, means associated with said first opening to provide first valve means for valving the flow of fluid through said first opening, control means for selectively controlling the amount of opening of said first valve means, said first valve means being selectively controlled by said control means between various positions of opening down to a position in which the flow is complctely cut off, means forming a discharge port between said intermediate chamber and said outlet chamber to permit flow of fluid from said intermediate chamber to said outlet chamber, said valve body being provided with a cylinder, means forming a bore between said inlet chamber and said intermediate chamber and forming a beveled seat surrounding said bore on the side of said partition adjacent said inlet chamber, means establishing a head chamber in communication with one end of said cylinder, said cylinder being in communication adjacent the opposite end from said head chamber with said outlet chamber; said cylinder, said port and said bore being spaced apart and being in axial alignment; a unitary piston assembly including a throttling member intermediate the ends thereof, said unitary piston assembly being slidably received in said bore and said cylinder adjacent opposite ends thereof with said throttling member being slidably received in said port, said unitary piston assembly being movable as a whole to carry said throttling member to various positions in said port to control the fluid flow from said intermediate chamber into said outlet chamber, said unitary piston assembly being provided with a seating portion adapted to cooperate with said beveled seat to substantially close oil any fluid leakage through said bore when said seating portion is seated thereagainst; said assembly having an effective area adjacent one end thereof exposed to fluid under pressure in said inlet chamber to provide a first force tending to carry said assembly in one direction towards closure of said port by said throttling member and tending to carry said seating portion towards seating, said assembly having an opposing area on said first piston opposite said effective area and exposed to fluid under pressure in said head chamber, means communicating said intermediate chamber with said head chamber whereby the fluid pressure in said intermediate chamber is communicated to said opposing area to provide a second force tending to carry said assembly in the opposite direction towards opening of said discharge port by said throttling member, said first force being greater than said second force whereby the net eflect on said assembly is a net force equal to said first force minus said second force which tends to carry said assembly towards closure of said discharge port by said throttling member, compression spring means biasing said assembly in a direction opposite from said net force so that with any given setting of said first valve means and with changes in the fluid pressure in said inlet chamber said assembly is moved to maintain the pressure drop across said opening substantially constant, thereby maintaining the flow of fluid through said valve as a whole substantially constant.

13. The valve according to claim 12 including a variable restriction valve means in said means communicating said intermediate chamber with said head chamber for adjusting the fluid flow from said intermediate chamber towards said head chamber to adjust the opening rate of said throttling member.

14. The structure according to claim 12 in which said piston assembly includes an area thereon disposed in the stream of hydraulic fluid flow through said port into said outlet chamber and arranged so that the increasing tension of said spring means acting on said piston assembly as it is moved in a direction towards closure of said port is compensated for by the increasing opposite force of the stream of hydraulic fluid impinging on said area disposed in the stream of hydraulic fluid flow.

15. In a hydraulic elevator control system having a jack cylinder and an elevator car supporting plunger reciprocable therein, means establishing a passageway including an opening therein and including a port therein, conduit means communicating said jack cylinder with said passageway whereby during descent of said elevator car supporting plunger hydraulic fluid is adapted to flow from said jack cylinder through said passageway and through said opening and said port, said port being located in said passageway downstream of said opening, normally closed valve means in said opening for stopping the flow therethrough to hold the elevator car at a stationary position, said valve means being movable in said opening to at least one open position of a given size to lower said elevator car supporting plunger, control means connected to said valve means for the opening thereof and operable responsive to the differences between fluid pressures upstream and downstream of said open ing, throttling means in said port movable therein to various positions for controlling the rate of flow through said port, and positioning means connected to said throttling means and sensitive to fluid pressure upstream of said opening for changing the throttling eflect of said throttling means in accordance with changes in fluid pressure upstream of said opening so that when said valve means is opened from said normally closed position to said open position the differences between pressures upstream and downstream of said opening follow substantially the same pattern regardless of changes in fluid pressure upstream of said opening, whereby said elevator 16 supporting plunger is accelerated uniformly to a given lowering speed regardless of changes in the fluid pressure upstream of said opening.

16. A unitary valve for maintaining a constant flow of fluid for any given setting of the valve and for maintaining a uniform acceleration of the fluid flow between various settings of the valve comprising a hollow 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 forming an opening between said inlet chamber and said intermediate chamber to permit flow of fluid from said inlet chamber to said intermediate chamber, means associated with said opening to pro vide first valve means for valving the flow of fluid through said opening, control means associated with said first valve means for controlling the amount of opening of said first valve means, said first valve means being selectively controlled by said control means between various positions of opening down to a position in which the flow is completely cut off, said control means including means operable responsive to the differences between fluid pressures in said inlet chamber and said intermediate chamber, means forming an opening between said inlet chamber and said intermediate chamber to permit flow of fluid from said intermediate chamber to said outlet chamber, said valve body being provided with a cylinder, means forming a bore between said inlet chamber and said intermediate chamber, means establishing an additional chamber in communication with one end of said cylinder, said cylinder being in communication adjacent the opposite end from said additional chamber with said outlet chamber; said port, said bore and said cylinder being spaced apart and being in axial alignment; a unitary piston assembly including a throttling member intermediate the ends thereof, said unitary piston assembly being slidably received in said bore and said cylinder adjacent opposite ends thereof with said throttling member being slidably received in said port, said unitary piston assembly being movable as a whole to carry said throttling member to various positions in said port to control the fluid flow from said intermediate chamber through said notches into said outlet chamber, said assembly having an eflective area adjacent one end thereof exposed to fluid under pressure in said inlet chamber to provide a first force tending to carry said assembly in one direction towards closure of said port by said throttling member, means communicating the fluid pressure in said intermediate chamber with said additional chamber and with portions of said piston assembly for establishing a net force acting on said piston assembly to urge said piston assembly in a direction towards opening of said port by said throttling member, compression spring means biasing said assembly in a direction opposite from said net force so that when said valve means is changed from one position to another said assembly is moved to cause the diflerences between pressures in said inlet chamber and said intermediate chamber to follow substantially the same pattern regardless of changes in fluid pressure in said inlet chamber, whereby there is uniform acceleration and retardation of the fluid flow regardless of changes in pressure in said inlet chamber.

17. A valve assembly comprising a body, means in said body establishing a passageway therethrough including an opening therein and a port therein, means for delivering fluid under pressure to said passageway whereby fluid is adapted to flow through said passageway and through said opening and said port, valve means associated with said opening, control means associated with said valve means for closing said opening from at least one eflec tive opening size to a completely closed position, said control means including means establishing a cylinder in said body, a piston slidably mounted in said cylinder, said piston and said cylinder establishing a chamber, a

first conduit providing communication between said passageway downstream of said opening and said chamber, means for selectively opening and closing said first conduit, said cylinder opening into said passsageway upstream of said opening on the opposite end of said piston from said chamber whereby the position of said piston is responsive to the differences in fiuid pressure between said chamber and said passageway upstream of said opening, biasing means urging said piston towards closure of said opening, when said first conduit is open and the fiuid pressure in said chamber is substantially the same as the fluid pressure in said passageway downstream of said opening said piston being disposed in a position to cause said valve means to establish one effective size of said opening, throttling means in said port movable therein to various positions for controlling the rate of flow through said port, positioning means connected to said throttling means and sensitive to fluid pressure upstream of said opening for changing the throttling effect of said throttling valve in accordance with changes in fluid pressure in said passageway upstream of said opening so that the diflerence between the fluid pressures in said passageway upstream and downstream of said opening is substantially constant at a given amount for any one given eflective size of said opening, conduit means providing communication between said passageway upstream of said opening and said chamber, said conduit means being effective when said first conduit is closed to raise the pressure in said chamher by said given amount to the pressure in said passageway upstream of said opening, when the pressure is the same in said chamber as in said passageway upstream of said opening said biasing means being effective to cause closure of said opening, the retardation of said flow through said opening during the closing thereof being determined by the rate of How through said conduit means during raising of the pressure in said chamher by said given amount, whereby said retardation remains substantially uniform regardless of pressure changes in said passageway upstream of said opening.

References Cited in the file of this patent UNITED STATES PATENTS 1,725,374 Rush Aug. 20, 1929 1,904,475 Kissing Apr. 18, 1933 2,560,948 Hannibal et al July 17, 1951 2,782,598 Gatwood Feb. 26, 1957 2,785,660 Jaseph Mar. 19, 1957 2,925,066 Thorner Feb. 16, 1960