US2500883A - Piston valve - Google Patents

Description

A. R. STONE PISTON VALVE March 14, 1950 Filed June 15, 1945 FUVEII MumrEll MIL INVENTOR.

ALBEF'U RIVINGTON STONE HIS ATTORNEY Patented Mar. 14, 1956 PISTON VALVE Albert Rivington Stone, Anneslie, Md., assignor to Gerotor May Corporation, a corporation of Maryland Application June 15, 1945, Serial No. 599,680

4 Claims. l My invention constitutes a continuation in part of my co-pending application for Letters Patent ,of the United States, Serial No. 594,279, led May 17, 1945, and entitled Hydraulic system, now Patent Number 2,441,339, granted May 11, 1948. It relates generally to an apparatus for metering uid systems and has particular application to a novel metering valve and method of operating the same for the accurate control of variable load hydraulic circuits.

One object of my invention is to provide metering apparatus of the general type disclosed which is simple, reliable, and highly eicient in operation and which, while of low first cost because of its comparatively small number of parts and easy assembly. nevertheless displays low wear and long life over intensive service. Y

Another object is to provide a metering valve of the general type described having the characteristic of leakage compensation under heavyduty, variable-load hydraulic service, being fully load-responsive with high sensitivity and close regulation in entirely self-adjustable and automatic manner and in the substantial absence of supervision, and this with substantially the same high degree of sensitivity throughout a wide control range.

Yet another object is to provide a metering valve of this general type whereby, from a constant volume source of hydraulic energizing uid, variable loads ranging above a, predetermined minimum load for which the system has been preliminarily regulated, can be serviced in efficient and automatic manner through a mechanism brought into play by leakage pressure occasioned by increase in system load.

Other objects and advantages will in part be obvious and in part pointed out hereinafter during the course of the following description.

My invention accordingly resides in the several elements, features of construction and combination of parts, and in the several operational steps, as well as in the relation of each of the same to one or more of the others, the scope of the application of all of which is fully set forth in the claims at the end of this specication.

In the drawings, wherein solely by way of illustration and not in a limitative sense I disclose one embodiment of my invention which I prefer at present. Figures 1, 2, and 3 are like sectional views in which in Figure 1 the valve is shown as closed, in Figure 2 the valve has been cracked slightly under manual regulation and is operating under minimum load conditions for that degrec of basic regulation, while in Figure 3 the main control adjustment remains as in Figure 2 but the valve has been further cracked in robotcontrolled manner due to leakage pressure which is attendant upon temporary increase of the load on the system.

So that more thorough appreciation may be had of the precise nature and scope of my present invention, it is interesting to note at this point that extremely important impetus Was given to the eld of hydraulic powering equipment when multi-chambered rotary hydraulic pumps and motors were first introduced on the market. It had long been recognized theretofore that basically, iiuid systems were fundamentally capable of a characteristic exibility and adaptability for widely varying load conditions which Vprobably surpassed by substantial margins practically all other types of powering equipment, even including electric motors. Nevertheless, the acceptance o'f such equipment in commerce and industries necessarily was drastically curtailed due to the substantial absence of satisfactory apparatus or mechanism for carrying these advantageous characteristics into use.

To illustrate, the familiar reciprocating pump, perhaps constituting the prototype of all present-day hydraulic equipment and itself still in service for many specialized operating conditions, possessed many fundamental deficiencies which eifectively precluded it from representing the epitome of hydraulic service. It was bulky, cumbersome, costly and uncertain in operatic-n. It required close supervision. Its pulsating, surgelike delivery even where costly equalizing domes were employed, detracted from its desirability.

While, for the rst time, surging pulsations were effectively eliminated upon the introduction into the field of the now widely-accepted singlechambered rotary pump, this pump was available only for low-pressure service. It wasquickly established that it could not develop sufficient force to work against pressure heads of appreciable magnitude. Leakage and slippage combined effectively to prevent high-pressure duty.

Upon the advent of the multi-chambered rotary pump, however, wherein the separate eiects of the several component pumping chambers were combined in additive relation, the picture was appreciably changed. For the rst time highpressure loads could be serviced in continuous non-pulsating manner. Full advantage could be taken of the characteristic flexibility inherent in hydraulic systems.

Flexible as is the hydraulic equipment which has been described, nevertheless it is subject to a diminished extent, to a limiting factor which is inherent in all powering equipment, that is, no type of prime mover, dynamo, or other powering equipment, either driving or driven, is capable of operating at its maximum efficiency throughout its entire operating range. Explained in other terms in order to emphasize this point, the entire operating range of practically all powering equipment is substantially greater than the relatively small portion thereof in which peak eciencies are obtainable.

The foregoing phenomenon is of no particular moment when loads are being serviced which are either constant or else are of limited variability in but a small number of denitely defined steps. In such instances powering equipment is selected, operable at maximum efficiency for the particular load being serviced. Where a small number of definite increments in load are involved, then two or more powering unitsmay be connected in l,

tandem or parallel, so that each unit operates at itsmaximum emciency, the total number of units being selected in response to the immediate load demands, so that at all times highly satisfactory system performance is achieved.

The situation is entirely diierent, however, where highly-variable loads are being serviced over a wide load' range. Ordinarily where such loads are powered directly' from a single powering unit, it is necessary to design the motive equipment such that it will adequately supply the maximuln load demand. Should the powering equipment be designed for service at maximum eiciency at or about this peak load, however, then the operation of such unit for normal load demand, below peak performancawill be at reduced eflciency, and hence with increased operational costs. On the other hand, should such powering equipment be designed for maximum eihciency at normal loads, substantially below peak load demand, then the risk exists that should such peak load demand persist for any unusual duration, damage may result tothe powering unit from continued operation in excess of its rated capacity. More practically, slippage and leakage would occur so that the powering equipment would refuse the load. All in all, this presented a very practical disadvantage which, prior to the'introduction of the system according to my said parent application was resolved, if at all, only by the addition of an auxiliary and somewhat parasitical regulatory adjunct to the powering equipment. Measured in the light of' practical tests, equipment provided with such auxiliary controls were unsatisfactory in performance. satisfy the demands, of the industries.

In accordance with the teaching of my said parent application, a radical departure was. had from the modes of control theretofore suggested in that, while these prior systems uniformly undertook to vary the output of the particular hydraulic powering unit in accordance with the instantaneous load demands; on the contrary, and following the teaching of my invention it was proposed to employ a constant output power unit, operating always at maximum efficiency, and then to meter the quantity oi fluid output of such con.-

stant-delivery unit which was directed to the load,

insensitive response totheinstantaneous load demands. In short, instead. of using a variable output powering unit. with complicated ,contr( ls,v

aponstant output. installation was employed with simple' metering means. Resultswere achieved superiorto vanywhich had theretofore been considered possible. ANotonly were rst costs low,.-

They did not .l

but maintenance and upkeep were materially reduced, and appreciably less supervision was required.

Despite the sensitive operation of such new system, it nevertheless required the services of an intelligent and highly observant operator to regulate the metering system in accordance with the observed variations in the load. Not only did this mean that there had to be constantsupervision, but there was necessarily some time lag between rst variation in the load and subsequent adjustments in conformity therewith, enduring for the norm-al reaction time of the operator. Such lag became appreciable upon wide and rapid fluctuations in the load conditions. To a certain extent at least, this rendered the system somewhat impractical for certain uses, as for example in the operation of a rolling mill and other equipment having repeated wide variations in load demands.

The improvements according to my present invention are directed to the removal in large measure of theV aforementioned disadvantages characterizingthe art as heretofore knowmand to provide a. fully automatic, somewhat robot-like control whichv quickly and sensitively compensates for all variations in load, introducing so much of the output of the constant output hydraulic powering equipment as is required to satisfythe immediate load demands for any particular normal regulation of the control mechanism, and being superbly adapted for rapid adaptation to and supply of loadsvariable in. rapid, irregular and unpredictable manner.

With the foregoing generalized picture of the objectives of my invention kept prominently in mind, reference is nowhad tothe three viewsl of the drawings for readily understanding the following, more detailed description.

It will be assumed that the metering valve s hown isinte'rposed in a hydraulic line between a sourceof hydraulic power of suitable conventional type, not shown, and which typically may comprise a Gerotor make, multi-chambered rotary pump on the one hand; and means for powering a variable load, such 'as' a hydraulic m0- (ill tor which similarly conveniently may be a Gerotor make, multi-chambered hydraulic motor on the other hand.. This motor likewiser is vnot shown, inasmuch 'as thedetails thereof do not per se form any part of this invention.

The present invention, and therefore, the present. disclosure, is c lijrected primarily to the control means, taking the form of a metering valve, which is interposedbetween the several units of powering equipment. As has been stated, the characteristic feature of the hydraulic pumpis that it is a constant speed constant loutputhydraulic unit operating always at ratedl maximum eiciency,` and with sufficient capacity to service properly the maximum` load. expected on the line. Thispump operates through-a closed system, returningdirectlyj to: the inlet sideof the pump all of the output iiuidy except that part lthereof which' at any instant is bled off tosupply thecinstantaneouss'load demands; It is the metering valve nowl tol be. described which 'staiitiall diamcter.. i. and

atod'eeeV I2. It terminates short of the top surface of the casing I Il in a machined wall I3.

Casing I is laterally ported as at I4 and I 5, these ports being let through the casing into the bore at calibrated points along the extent of the bore near the upper end thereof, and preferably being diametrically opposed to each other. In the instance undergoing description, port I4 comprises the admission or inlet port, while port I5 comprises the outlet port. In the preferred embodiment, these ports are disposed horizontally and radially. It is entirely feasible, however, to arrange them in tangential manner and at any desired angle to the horizontal.

Channel i@ leads from the constant delivery source of fluid power through the casing Ill up to the admission port I4. Similarly, channel II leads from outlet port I5 through casing I ll to the load, not shown. Within the casing I0, a branch channel I8 leads from a generally T connection with channel II to a port I9 letting into the top of bore II through machined wall I3. Preferably channel I8 extends vertically and centrally through wall I3.

A skirted piston indicated generally at 2II is disposed for reciprocation in the bore II, motion being imparted to the piston 2@ by a centrallydisposed and downwardly-extending piston rod 2|. The skirted portion of the valve 2t serves to control the degree of opening of ports Ill and I5. Its primary function, however, may be said to be the control of the admission or inlet port I4. Its simultaneous control of outlet port I5 is entirely incidental to its control of the inlet port.

Piston rod 2| has an extent substantially less than that of the bore II, the construction being such that at no time does the outer end of rod 2| protrude beyond the confines of bore Ii. At its lower or outer end, rod 2| terminates in a pressure plate 22 which, while of moderate thickness, is of substantial diameter, only slightly less than that of bore I I.

A cam follower rod 2i! is disposed in the prolongation of the axis of piston rod 2l, so that the two elements are coaxial. This rod 23 extends into the ybottom of bore II from the lower exterior, and normally terminates short of the pressure plate 22. A cam follower 24 serves as a head for the lower end of follower rod 23 and may be of any suitable configuration. In the present instance, this conveniently is cylindrical, to conform with the surface contours of the cooperating control cam. This control cam 25 preferably is of the disc type and operates off of a manually-rotated control shaft 26. Shaft 26 is operated through a manual crank or other suitable control means, conventional in the art, and not shown.

The function of the manual control means, including shaft 26, cam 25, follower 24, etc., is to regulate the piston valve initially so as to provide desired calibrated cracking of the admission port I4 for typical mean load conditions prevailing for the operation undergoing energization.' It is desired to provide in some conventional manner that the cam setting be self-locking in nature, so that variation in load conditions will not produce corresponding variation in the cam positioning until the operator intentionally manually readjusts the same. Either a shaft lock is provided for shaft 26, or' the design of the cam profile allows for thisrequirement, while at the same time providing for calibrated cracking-of the-admission' port I4. Either such expedient is conventional in the art and needs no further de-r scription here.

Snugly received in the bore |I near the lower end thereof is a cylindrical box-like housing 21 which is machined and finished for ready reciprocation within the bore II. It is made fast to follower rod 23, which extends centrally therethrough, in any suitable manner at 28, as by welding, soldering, spinning or the like.

Pressure plate 22 is disposed interiorly of this box-like hollow cage member 2l through an opening 21A provided centrally in the top of this latter member. The pressure plate 22, which is attached to the piston rod 2| in any desired and suitable manner itself entirely conventional,

is inserted into cage 2'Iby the use of any suit--` able manufacturing technique, as by radially slitting the top surface 21B to cage 2l to form wingportions, bending these wings backwardly to provide an opening, inserting the plate 22 within the hollow cage, and thereupon folding down the wing portions, and if desired, sealing them as by seam welding, soldering or the like.

Interposed between the pressure plate 22 and the interior bottom 2'IC of cage 21 is a coiled spring 28B. Spring 28B encircles follower rod 23 within cage 2'I and is secured to the bottom interior of such cage, on bottom plate Z'IC, in any suitable manner at 23 as by soldering, welding, or the like. This spring 28B rests freely against the under side of follower plate 22 and serves as a resilient buffer therefor.

I provide what I term an annular stub 3D within bore II, nearly centrally thereof and about piston rod 2| which extends freely therethrough a central bore 30A. This stub 30 is secured to the walls at 3| of the casing I0 in any suitable manner at its outer periphery, as by welding, soldering, or the like. I dispose stub 3i) at a point within bore II which is appreciably above the maximum upward travel of hollow cage 2I under the impetus of cam 25. Figure 1 discloses the cage 21 at its maximum upward position, being so positioned by cam 25, corref sponding to full closure of inner port I4.

Stub 30 serves as a reaction plate against which a coiled spring 32 reacts in its downward thrust against the topy surface 21A of cage 2l.'

Spring 32 is disposed concentrically about piston rod 2|, and is secured at 33 to the top side 27B of cage 21 in any suitable manner soldering, welding, or the like.

In profile or section, the generally cylindrica skirted piston valve 20 has what I term a gen' erally curved side wall or generatrix Si which is of calibrated contour, and which may have a surface of hyperbolic, parabolic, or other configuration developed either in accordance withv natural or empirical equations, the prerequisite being satisfied, however, that calibrated and de-` sired cracking of the admission port III is accomplished upon movementof piston valve 2li. To illustrate, were the piston valve'il to be fully cylindrical, then the admission port 'I4 would remain fully closed until at such time as the extreme top surface of the valve 20 began to clear the port lli. At that time, and not before that point is reached, port It would begin to open quickly, with a rapid surge of power and with a minimum of wire drawing. Sensitive cont-rol, however, would be absolutely lacking.

By properly contouring the walls of the valve 2D, however, and upon calibrated departure from the straight line generator of the true-cyl-I inder, and by employing thev curved generatrix hereinbefore described, it is possible to shape valve 20 so that the cracking of the port I4 is sensitively in conformance with the instantaneous load requirements, That is, when the valve 20 is moved but a slight distance down from its closed position shown in Figure 1, generatrix 34 still remains closely adjacent port I4 and cracks the same but a slight amount. Only a small amount ci energizing fluid courses across the bore II to the outlet port i5, which likewise is" cracked but a small extent. Only minimum loads can be serviced.

A further like increment of vertical movement, however, presents a portion of generatrix 34 opposite admission port i4 which is more remote from the latter. An appreciably greater increment of energizing fluid thereupon courses port I4 and bore II to port I5 and thence to the load. Upon still further downward movement of piston valve 2o a like increment, the correu sponding cracking of port iIll becomes much greater, in a manner which will be readily understood. Due to the departure 'of generatrix 34 from proximity to port I4, a progressively greater quantity of hydraulic fiuid will course -fthe hydraulic load circuit. It will thus readily be seen that the opening of admission port It is a power function of the increment oi vertical displacement of valve 2i). It is unnecessary,

however, that this power exponent be an integral number, and its value determines the preoise shape of the generatrix 34.

It is desirable to repeat at this point that as the fluid from the constant output power source,

not shown, is diverted through admission port I4 r to the variable load, the quantity of fluid re turned directly to the low pressure, inlet side of the power source is correspondingly diminished. This is because the return line fromy the load is returned in closed hydraulic circuit to the system reservoir. The total quantity of fluid per unit of time by the main, constant delivery pump, however, remains always substantially the same. It is in this closed hydraulic circuit that my new metering valve is inserted in series connection.

To understand the operation of my new metering valve under manually-operated cam control, let us assume that no-load conditions exist, corresponding to the showing in Figure 1. Admission port I4 is entirely closed. The shaft 26 is rotated so that cam 25, in its topmost position, forces follower 24, follower rod 23, and cage 2l' to their uppermost extent relative to bore I I. Spring 28B bears resiliently against pressure plate 22 just to the under side of piston rod 2li, and forces this pressure plate up against the under side of top plate 27B of cage 27. Against the compression of spring 23 thrusting off of annular stub 33, the plate 22, piston rod 2l, and piston 20 are forced by'spring 28B, carried in cage 2'I, to the top of bore II, the substantially cylindrical lower part 35 of the skirt of piston 2G then being opposite admission port I4.

During rest conditions, spring 28B ensures that piston 20 is retained at or near the upper limit oi its travel in bore I I, effectively closing admission port I4. Y

What has been described to this point comprises simply the control of the piston valve 2B relative to the admission port I4 for any given manual setting of the piston valve 20 through the cam 25 in a manner fully detailed` in the foregoing. It is oi course apparent that the widest and most sensitive latitude of adjustment is available through the manual control. That is, in continuous as distinguished from step by step control,y

the piston valve can be adjusted from one extreme position wherein the admission port I4 is fully closed, substantially to its other extreme posie tion, wherein the admission port I4 is nearly opened.

Throughout the range of intermediate positions and in dependence upon the momentary valve position a corresponding fraction of the constant output deilvery of the hydraulic powering unit,v not shown, is passed through admission porti 4 to the hydraulic load. For constant load corre-'- spending to the particular cam setting, no more regulation is required. If load variation is infrequent and slow, then rather satisfactory results can be achieved simply by manually varying the setting of cam 25, and hence of piston 20, to correspond with the variations in load demands.

Ii, however, the load variation be frequent, unpredictable, and somewhat rapid, then not only is the required supervision of the control so great as to render its use for such purpose impractical, but even if continuous supervision is provided, the control is not suiiiciently responsive or sensitive to accommodate for the rapid fluctuations which occur. A robot or automatic control is indicated.

To provide for such automatic regulation, I construct the top surface of the piston valve 211 at the break 34A at the top of generatrix 34, with a substantially plane-surfaced header 35, the outer periphery of which is substantially of the same radius of curvature as, and conforms with the periphery of, the bore i i and is smoothly slidable therein. At its periphery, an annular upstanding ange 35A is provided, which forms, together with bore II and end wall 13, a circular recess 36.

This top plate 35 serves to transmit leakage pressure which occurs in the conduit I'i, and is transmitted to the topside of such plate, to the pressure plate 22 at the lower extremity of piston rod 2l. There, this excess pressure is algebraically compounded on spring 28B and overcoming the same, serves to urge it downwardly, against the upward force exerted by the spring itself. Pressure plate 22 thereby forces the spring 28B downwardly to a certain extent, the maximum extent of which movement is determined by the contact of plate 22 with the upper end of cam follower rod 23.

It has been stated that pressure on the top of valve plate 35 and hence in recess 35, which iiuid pressure is exerted through port I4 from bran-ch conduit i8 and conduit I'I, is the result of pressure build-up in this last-mentioned conduit.

,-. This pressure, which may accurately be considic motor, for example, a back pressure builds up which causes increased fluid leakage about the moving parts of this motor. In response thereto. a back pressure builds up in the conduit I'I, and there being no channels for pressure relief other than through the branch conduit I8, this increased pressure is imposed on the top side of valve 2B, at plate 35. The latter is moved downwardly against the force of the calibrated spring 28B in the manner narrated hereinbefore, to crack iur- 75 ther the admission port I4 in graduated manner inl` 9 dependence upon' the momentary increase in load. Thus, leakage compensation, and hence load compensation, is provided for in highly sensitive and accurate manner, within substantial limits, for any particular manual setting of the valve 2U through cam 25. The manner in which this oper- 'only to the extent provided for by the cam control means. This corresponds .to minimum load conditions for such valve setting, on the hydraulic motor. Only enough iiuid courses port Ill from the hydraulic pump as is required to service such load.

Let us assume, however, that this load on the hydraulic motor serviced through this metering valve momentarily increases, and that such load increase is to be accommodated by robot control through my auto-matic metering valve, without further adjustment of the cam 25. This automatic action results, as has been disclosed, from leakage pressure build-up in channels ll and i8. When this pressure is exerted on the top side 35 of piston valve 2i) (Figure 3), it moves this latter downwardly to a graduated extent, the maximum limit of which is determined by the contact of pressure plate 22 at the end of piston rod 2l with the top end of cam follower rod 23. This limit position is clearly shown in Figure 3, wherein it is also to be noted that a space 3l here separates follower plate 22 from the top surface 21B of hollow cage 2l. Moreover, it is to be noted that in this position it is the increment 34C of the curved generatrix 34 which is opposite admission port Ill rather than the portion 34B thereof, as is true in the case of Figure 2. Accordingly, substantially greater unit volume of fluid courses port lll, corresponding to increased load demands on the hydraulic motor.

My new construction responds admirably to the accurate and sensitive control of widely varying loads, and this with operation at maximum efficiency of a constant delivery hydraulic pump. As is clearly disclosed in my said parent application, it is entirely feasible, where desired, that in addition to being of constant output, this energizing source may have constant direction characteristics, in which case valves may be employed, for determining the direction of energization of the load-energizing motor.

In the instance that the load demand on the system increases beyond the robot control compensation permitted by the movement o-f piston 2li through the distance 3l, then further compensation to a new normal or mean value can be achieved through further throw oi the cam 25 into a new position. After such further adjustment, the cage 2l is lowered to a new point, so that contact is resto-red between pressure plate 22 and top surface 2lB of cage 2l. Compression is removed from spring 28B. Spring 32 insures that the cage 2'! closely follows the cam 25, and tends to overcome any frictional resistance of the cage 2l' relative to the bore l l and to assist in centering the cage therein. Further robot control can now be achieved, in a manner and mode fully corresponding to that described.

The rugged and simple nature of my new construction is readily apparent from the foregoing. It may be further readily observed from my disclosure that in direct, simple, and reliablemanner the several objects of my invention, including among them automatic and sensitive leakageand load-responsive regulation and high sensitivity with wide control range, are accomplished, together with many thoroughly practical advantages.

Inasmuch as many embodiments may be made of my invention, and since many modications may be made to the embodiment herein disclosed, it is to be understood that the foregoing disclosure is merely illustrative, and not in any sense to be construed as limitative.

I claim as my invention.:

l. A hydraulic metering valve -for supplying energizing iiuid to a variable load, comprising in combination, a valve casing having a central bore and having inlet and outlet ports therein, a rodded piston valve displaceable in said bore, and having a working surface of calibrated contour for calibrated passage across said inlet port, said piston valve having an enlarged head portion and said casing having a channel leading from the outlet side of said bore to the top end of said bore, said piston rod terminating in -a pressure plate, a manually-operable cam for initially setting said piston valve to open the inlet port a predetermined amount, a cam follower rod carrying a hollow cage member, slidable in said bore, and within which member the pressure plate of the piston rod is received, a spring extending between the top side of said hollow member and a stud provided within said casing, and a second spring provided between said pressure plate and the bottom interior of said hollow member, normally separating said two rods and yieldable to back pressure on said outlet in excess of a certain value transmitted to the top side of said piston thus displacing the latter and providing further admittance through said inlet port.

2. A hydraulic metering valve for supplying energizing fluid to a load in accurately metered quantities, comprising in combination, a valve casing having inlet and outlet ports therein, a valve piston displaceable in said casing for modifying the eiective opening of at least one of said ports and having an end susceptible to a displacing pressure of fluid, and means for moving said piston to desired controlling relation with at least one said port and including adjacent members -spring urged one toward the other for movement in unison to initially set the piston and susceptible to relative movement by pressure of iiuid in excess of a certain value exerted on said piston end, for modifying the specic initial piston setting.

3. A hydraulic metering valve for supplying energizing fluid to a load in accurately metered quantities, comprising in combination, a valve casing having inlet and outlet ports therein, a valve piston displaceable in said casing for modifying the elective opening of at least one of said ports and leaving an end susceptible to a displacing pressure of fluid, means for moving said piston to desired controlling relation with at leas-t one said port and including adjacent members spring urged one toward the other for movement in unison to initially set the piston and susceptible to relative movement by pressure of fluid in excess of a certain value exerted on said piston end, for modifying the spe- [cie initial setting, and lspring means biasing both vof :said overlapping members in favor :of one `direction 'oi vrnovernentof the -ipiston to iniltial setting.

i4. A :liydrenulic metering Valve .for supplying Yenergizing fluid in vaccurately metered quanti- `ties, :comprising in combination .a -valve easing .havmg agpston bore and inlet and outlet ports .through :the Wall vthereof, fa, nodded valve :piston 'fitting Within said bore for modifying the eec- :tive opening of at least :one yof .said ports and having an end .susceptible .to pressure of said 'energizing iiuid, and means for Yvariablv.setting l:seid piston :to desired controlling :relation with 'atleast-ione seid port and including a .member receiving the valve pistonmodr'andzslidable Ialong the casing lbore for adjusting .the vdesired vposi- .tion` of -hhepistonl said .piston rodlhaving a biased .212 `,plante voverlapping A#me vinside -surfaue mf :said 1re- `ceiving 4member `and being separable .lfrom 'itl-re 'seme by npifessure 'in :excess of -a `certain value on seid ipiston leni :in a given vsetting fof bhe le of this patent:

UNITED STATES PATENTS Number .Name Date 501,959 Rawlings y`'J1`i.l vf25,218553 .536,461 *Wadsworth .m .May `Tv, 11925 @020,773 '.'Ernst ,."Nov, 12, 51935 2=,061;852 fSohweitzer Nov. 24,21936

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