US2659349A - Hydraulic servo mechanism for gas turbine fuel regulators - Google Patents

Description

Nov. 17, 1953 N. E. STARKEY 2,659,349

HYDRAULIC SERVO MECHANISM FOR GAS TURBINE FUEL REGULATORS Nov. 17, 1953 N. E. STARKEY 2,659,349 HYDRAULIC SERV@ MECHANISM FOR GAS TURBINE FUEL REGULATORS Filed July 50, 1952 2 Sheets-Sheet 2 POSITION 5649 Inventor-z Neal E Starkey,

by unmix?.

' His Attorney.

Patented Nov. 17, v`1953 HYDRAULIC SERVO MEGHANISM FOR GAS TURBIN E FUEL REGULATORS Neal E. Starkey, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application July so, 1952, serial No. 301,616 2 claims. 1(c1. iai- 41) This invention relates to hydraulic servo-devices, particularly t9 a combination of hydraulic servo-mechanisms for use in the fuel regulating system of `a thermal pow erpl ant, such as a gas turbine.

While not necessarilylimited thereto, this invention is particularly kadapted for use in a gas turbine fuel system of the general 4type shown in the copending application of Bruce O. Buckland, Serial No. 183,332,1 ed September 6, 1 950 and assigned to the same assignee as the present application. Generally, such a fuel system ccmprises a variable dispiacemerit pump connected to Supply a liquid .fuel'sugh as diesel 0r BunkerfC oil to a plurality o fnoazles in the gas turbine combustion system. The displacement of the fuel pump is automatically varied lby a hydraulic servo-device actuated by a variable contro1 oil pressure signal, vwhich is supplied `bya regulator containing a complex combination of various condition-responsive servo-devices cooperating 'to produce the variable control oil pressure. Hereinafter, this variable pressure signal which acts on the fuel pump servo to determinethe rateof fuel supply will be referred to as the VCO pressure.

Another gas turbinefuel system of atype which may protably incorporate the presentinvention is illustrated in United States patent to N. E. Starkey et al., 2,558,592,1issued June-26, 1951,.and assigned to the same assignee as the presentrapplication.

The general arrangementlof the specific powerplant for which the present invention-Was developed, and other details of the regulating system therefor are disclosed in the United States patent of George R. Fusner and Chapman J. Walker, No. 2,617,253, -issued November 1'1, 1952, and assigned to the same assignee as the present application. This powerplant is characterized by a two-stage gas turbine with mechanicallyindependent rotors, one of which drives a low pressure compressor inseries with a high pressure compressor driven by' the other turbine rotor. The fuel pump is alsovdriven from thehigh pressure compressor rotor. 'I his means that, for a given setting of the fuel pump regulator, the rate of fuel supply will be a function of vhigh pressure compressor shaft speed.V As will beappreciated by those skilled in the art, the volume rate of air flow through the -high pressure compressor to the combustion system is al function'` of the rotational speed ofthe highpressure compressor. -But, since the loW pressure compressor is driven ata variable speed by its independent turbine rotor, the weight `ing a hydraulic piston rcondition by thek VCO ,calibrated s pring,.=.vith aY pilot valve for establsure responsive bellows rate of air flow through the system is also a function of the density or'pressure at theinlet tothe high pressure compressor. Thereforein order to make the Afuel regulating system accurately responsive to the Weight vliow of air, it isnecessary that the fuel regulating system incorporate means for sensing the pressureat the inlet to the high pressure,compressorl Accordingly, ytheobject of the v present invention iS t0 provide an imnroredhydlaulc SCWO-mecha# nism for a gas turbine fuel regulatingsystemof the type described including means A'for modify- .ine lthe VCO ,fuel rate pressure .Signal in attardkance with the inlet pressure of the high pressure compressor.

A further object is to provide an improved hydraulic regulating component of the ytype described, kin which the VCO pressure -is balanced directly againsta calibrated fmainspring'f.y and ,the .modifying are@ ofthe high Mesure 0,9m,- pressor inlet pressureis introduced ata point between the VCO .piston and .the Pilot velrerhicll ,determines v,th-'e VCO pressure, in order to `improve the Sensitivity Q'f' ihe'ofhiinisrrby 'fedro- .ing friction effects in thecompressor pressure responsive modifying mechanism.

Other objects and advantages will become apparent from ythe follovvingdescription takenin connection Withthe accompanying draivin'gsJ in which Fig. 1 is a diagrammatic representationof a gas turbine powerplant vvith a fuel system, hav ing, `hydraulic servomechanism in accordance with theinvention, the servo-mechanism being shown in section in more detail, and Fig'. 2 a graphical representation of the performance of the regulatin g mechanism to show theeiectof the invention.

Generally, the invention is practiced by provid' maintained in equilibrium pressure acting against a lishing the VCO pressure, and a compressor pres- ,connected to produce a .modifying effect on thelinkage whichconnects .theVCO piston withthe pilot valve.

Referring now more; particularly toFig. l, the

.inventionis show-nas applied to agasturbine powerplant .comprising a 10W pressure compressor Liconnectedin series kwith a high pressure compressor 2. a combustionsystem, and v,atwostage turbine vIl. The conduit Econnecting the compressors contains an intercooleri, andthe conduit connecting the high pressure compressor with the combustion sytinbntain's'a regenerator 6a in which Waste heat from the exhaust gas is transferred to the high pressure air on its way to the combustors. It is to be particularly observed that the two-stage turbine 4 comprises a first stage rotor a directly coupled to the high pressure compressor rotor, and a mechanicahy independent second-stage rotor 4b directly coupled to the low pressure compressor rotor.

rlhe variable displacement fuel pump is shown at 1 as connected to an accessory drive pad 8 and driven at a speed proportional to the speed of the high pressure compressor by suitable gearing (not shown). Also driven from the accessory pad 8 is a second positive displacement pump 9, the function of which is to provide hydraulic operating liquid for the fuel regulating system. It will be understood that the pump 9 furnishes control oil at a constant pressure, as determined by suitable pressure regulating valve means (not shown), and this constant pressure control oil will be referred to hereinafter as constant control oil (CCO) The variable pressure signal (VCO) for altering the displacement of the fuel pump 1 is communicated to a hydraulic servo-device indicated diagrammatically at 1a in Fig. 1. 'Ihe exact mechanism by which this servo determines the stroke of the fuel pump need not be described here, being disclosed more particularly in the above-mentioned application of B. O.

Buckland, Serial No. 183,332. In order to understand the present invention, it is necessary only to note that the VCO pressure supplied to the servo-device 1a varies the stroke of the fuel pump 1 so that the fuel supply rate to the combustion system is a joint function of the VCO signal pressure and the high pressure compressor shaft speed. In Fig. 1, the fuel pump is shown connected by a conduit I with a spray nozzle II in combustor 3a. It will of course be understood that similar fuel supply conduit means are provided for the other combustors. The details of the combustion chambers, fuel nozzles, and the arrangement of piping through which the fuel pump supplies oil to the combustors are not material to this invention.

Referring now to the hydraulic servo-mechanism to which the present invention specifically relates, it will be seen in Fig. 1 that the housing I2 defines a bottom chamber I3 closed by a cover plate I3a, a top chamber I4 closed by a cover plate I4a, a left side chamber I5 with a cover plate I5a, and a right side opening I6 closed by cover plate Ia. The constant pressure operating liquid is communicated by the CCO supply conduit 9a to an inlet port I1 in the left-hand side of the housing, and a second inlet port I8 in the bottom of the housing. The VCO signal pressure, which is the useful output" of the device, is communicated to the fuel pump servo 1a by the VCO conduit 1b, which communicates as shown in dotted lines with a port I9 located approximately at the geometric center of the housing I2.

The hydraulic servo-device comprises the VCO piston assembly indicated at 20, the VCO pilot 2|, and the compressor pressure responsive servo indicated generally at 22. Generally stated, the function of these components is that the pilot 2| controls the supply of CCO operating liquid to the VCO piston 20, and the compressor pressure compensator 22 alters the characteristics of the linkage which connects the VCO piston with the VCO pilot.

Referring now more particularly to the construction of the VCO piston assembly 2D, it will be seen that the movable piston member 23 is' actually a plunger member denning a cylindrical recess 24 in which is shdably disposed a piston member 25. Piston 25 does not move longitudinally relative to the housing I2, but is rotataoly supported in a bushing member 26. The projecting end portion 25a carries a gear 21, the function of which will be seen hereinafter. Piston 25 may be provided with a plurality of circumferential grooves 28 for improving hydraulic balance, in a manner which will be understood by those skilled in the art. The piston 25 and the moving cylinder member 23 cooperate to define a pressure chamber 2s to which the VCO signal pressure is communicated by a transverse drilled hole shown in dotted lines at 3U communicating with a longitudinal drilled hole 3 I.

The VCO pressure existing in chamber 29 produces an upward force on the VCO piston 23 which is balanced against a carefully selected coil spring 32. This spring surrounds piston 23 with the lower end thereof engaging a radial end flange 23a, the upper end of the spi-mg seating in a cylmdrlcal recess 33a of a threaded bushing member 33. It will be apparent in rig. 1 that the moving VCO piston 23 passes freely through a cylindrical opening 33b in bushing 33, with generous radial clearance therebetween. Thus, it will be seen that piston 23 is positioned freely by the VCO pressure in chamber 29 balanced against the calibrated spring 32. The force exerted by spring 32 may of course be adjusted somewhat by varying the depth to whichthe threaded bushing 33 is screwed down into the housing portion receiving it. The lowermost position of piston 23 is determined by engagement of the lower end flange 23a, with a stop member 34, which may be an anti-friction bearing slipped over the reduced diameter piston portion 25h before piston 25 is inserted in the bushing 25 and the gear 21 assembled. It will be apparent in Fig. 1 that gear 21 is keyed to the shaft end portion 25a, and may be retained by any suitable means such as the snap- It is also to be noted that the VCO liquid is supplied to an annular groove 26a in the outer circumference of bushing 26 by way of a passage I9a communicating with the VCO port I9. From the annular channel 26a, liquid is communicated by a plurality of circumferentially -clearances between bushing 26 and the housing is prevented by a pair of O-ring seals 35, 38, the arrangement of which will be obvious from the drawing.

The condition shown in Fig. 1 represents the minimum VCO pressure, with piston 23 at the bottom of its range of movement against the stop member 34.

The VCO pilot assembly 2l comprises a longitudinally movable pilot spindle 31 having a pair of axially spaced lands 31a, 31b connected by a reduced diameter portion 31c and slidably disposed in a bushing 38, having an axial bore 38a. Bushing 38 is rotatably disposed in a second bushing member 39, which may be retained in place in the housing by an upper end flange 33a and a snap-ring 39h engaging the lower end thereof. Keyed. to the upper ejnd of the rotatable bushing 38 is a gear 40; and a second gear 4| is keyed to the lower end of bushing 38 s0 asv to engagev with gear 21 on the rotatable piston member 25.l Gear 40 may be conveniently retained by snap-ring 40a, and gear 4| may be secured by snap-ring 4|a. i

The purpose of these gears is to effect continuous rotation of the pilot bushing 38 and the piston member 25 in order to reduce friction effects between piston 25 and the VCO piston 23, and between the pilot 31 and its bushing 33, respectively. The idea of thus rotating one of a pair of cooperating sliding parts to reduce friction effects therebetween is not a part of the present. invention. Such rotational movement of bushing 38,` and piston 25 is produced by a worm gear 42 carried on a shaft suitably journaled in the housing I2,y the mechanical details of which are not important to the present invention.

Operating liquid is supplied from the CCO inlet port |8 by way of a passage lila to an annular groove 43, communicating by Way of a plurality of circumferentially spaced ports 44 with cooperating ports 45 in bushing 38. The annular space 31d surrounding the pilot spindle portion 31o communicates by way of ports 46 with an internal annular groove 41 and a plurality of spaced` ports 48 in bushing 39. Port 48 communicates by way of conduit |9b in the housing with VCO port |9.

Bushing 38 also denes a plurality of spaced ports 4,8 cooperating with ports 58 and an annular drain groove For eiectingr free discharge of spent operating liquid from groove 5|, the housing is provided with an axially extending slot shown at 52. This permits free egress of operating liquid past the end flange 39a and the generously proportioned recess in which gear 43 is disposed.

The compressor pressure compensator 22 comprises a pressure responsive bellows assembly indicated generally at 22a and a hydraulic forceamplifying servo indicated generally at 22h.

The bellows assembly 22a comprises a cylindrical housing member 53 threadedly received in cover plate |3a and secured in adjusted position by a lock-nut 54. The axial bore through the tube member 53 contains an end seal member 55 retained by an internal snap-ring 56, with iluid leakage between the tube 53 and seal ring 55 prevented by an O-ringr seal 51. Disposed in the tubular housing 53 is a flexible bellows 58 having its lower end sealed to the ring member 55, high pressure compressor inlet pressure being communicated by conduit 5b to the interior of bellows 58. The upper end of the bellows is sealed to a tting 59 which serves as a seat for a biasing coil spring 60, the upper end ofwhich abuts a washer 6| secured by a snap-ring 62. The bellows end tting 59 also carries a transverse pivot 63 by which the motion of the bellows is communicated to the pilot rod member 64.

The hydraulic amplier assembly 22h comprises the pilot rod 64, having axially spaced landsv 64a, 64b separated by a reduced diameter portion 64C. Pilot 64 is slidably disposed in the axial bore 65a of a piston member` 65 which is in turn slidably disposed in a cylinder member 66. Cylinder 6,6 may be conveniently retained ina lrecess in the housing by an internal snap.-

'ring shownat 61` The upper portion of cylinder 65 denes a chamber 66a, the upper end of which pressure supplying Whatever is closed by a vseal ring 68.- Rns member 68 may be retained by ari internal 'Snap-rios 6,8 and nuid maltese between ring 68 and the .Outer surface of piston member 65 is prevented by Van Owing seal 68a. It will be seen that the piston portion 65h of the member 65 cooperates with recess 66a to denne an upper pressure chamber 10 and a lower pressure chamber 1|.

The hydraulic passages in the amplifier 22h are as follows. The constantv pressure CCOr oil from inlet port |1 is supplied to an annular groove 12 in the outer circumference of cylinder member 66, whence it passes by way of several drilled holes 13 to an internal annular groove 14, which communicates with several circumferentially spaced holes 15 in piston member 65. By way of these passages, CCO oil is supplied continuously to the annular space 16 der lned between the spindle portion 64e and the bore 65a of the piston 65. Downward movement of pilot spindle 64 causes the lower land 64a yto uncover another set of ports 11 so that oil is admitted by way of a communicating axial pas.- sage 18 to the upper chamber 10 deiined above piston 65h. Such downward movement of pilot spindle 64 also causes the upper land 64b to uncover a set of drain ports 13, so that liquid trapped below the piston 65h leaves the chamber 1| and is discharged through the top portion of bore 65a and through one or more transverse drilled holes 80.

Conversely, upward movement of pilot spindle 64 causes operating liquid from thev annular space 16 to be supplied by way of the passages 18 to the lower chamber 1|, forcing piston 65h upwardly, while operating liquid trapped in chamber 10 leaves by way of theaxial passage 18, beingdis.- charged downwardly past the land 64a and out through the generous clearance space dened between spindle 64 and the adjacent wall of bore 65a.

Those skilled in the hydraulic servo-mechanism art will appreciate that this arrangement is merely a hydraulic power amplier for producing a displacement of piston 65 proportional to the input movement of the pilot spindle 64 effected by the iiexible bellows 58. This permits use of a comparatively small and light bellows 58, since the bellows need exert a force only suilcient to position the pilot spindle 64, hydraulic power is required to effect the compensating adjustment described below.

The mechanical linkage by which the VCO piston 20 is interconnected with the VCO pilot 2i and the compressor pressure compensator 22 produces its modifying effect is as follows.

The principal member of the interconnecting linkage is a floating lever 8| having a middle portion connected by a pivot 82 to the upper end of VCO pilot spindle 31. The right-hand end of lever 8l carries a cam follower roller 8-3 engaging a contoured cam 84 carried on a transverse shaft 35 journaled in the housing and arranged to be positioned bykexternal means, the precise nature of which need not be noted here. For purpose of illustration, the cam positioning means is represented by the manual handle 85a.. It is to be noted that the handle 85a is in the on position, with cam 84 rotated clockwise as far as it will go, so as to position cam follower 83 to the uppermost point in its range of movement.

.In simpler, uncompensated, hydraulic .servomeehanisms of this general type, the left-hand end of lever 8| bearsdirectly against the rounded ppere'nd 23h of the VCO piston 23. In accordance with the present invention, however, there is interposed between piston end portion 23h and the lever end portion 8|a a transversely adjustable roller 88. This adjustable abutment roller is journaled at the right-hand end of a lever 81 which is, at its left-hand end, pivoted at 88 to a shiftable block member 89 slidably disposed between upper and lower guide members 80, 8|. The central portion of block 89 is provided with a transverse recess 92 across which extends a pivot member 93 engaging the forked end of a lever 84, which is in turn carried on a pivot 95 secured in the housing. As seen in Fig. 1, lever 94 pivots from the position shown in full lines to that indicated in dotted lines at 94a. The lower guide member 9| is provided with an opening BIa which is of course of sufiicient size that motion of the lever 94 will not be obstructed.

The lever 94 is actually a sort of bell-crank havving a forked lower end portion 94h carrying a transverse pivot 86. Pivot 9G passes through a transversely elongated slot 91 formed in the extreme upper end portion of piston member 85.

It will be apparent from the above description of the mechanism that vertical movement of piston 85 will cause bell-crank lever 94 to rotate about pivot 95 so as to effect transverse sliding movement of block 89 and adjust the abutment roller 89 transversely relative to VCO piston 23. It is also to be noted that the adjustable bloei: 89 is shown in its extreme right-hand position. The extreme left-hand position corresponds to the dotted lever position 94a, in which roller 8S is in the position indicated by dotted lines at 88a as being directly over the end portion 23h of the VCO piston. It will be understood that, when the abutment roller is in this dotted position 88a, the compensating mechanism has no effect on the lever 8|, and the VCO piston 23 acts on lever 8| precisely as if the compensating roller 8B were not present. On the other hand, when roller 88 is displaced to the right of the dotted line position 35a, a special compensating eiect is introduced into the linkage, the degree of this compensation being of course proportional to that called for by the compressor pressure responsive bellows 58.

In order to maintain lever 8| properly seated against the roller 88 and the cam 84, a comparatively light coil spring 98 is interposed between a socket formed in the top cover plate |4a and the upper end fitting 31f of pilot spindle 31. rl'he downward force of spring 98 is just sufficient to maintain good contact between lever 8| and the roller 88 and cam 84 respectively, this spring force being so small as to have no effect on the positioning of VCO piston 23, etc.

In normal operation, spent operating liquid draining from the hydraulic amplifier 22h and from the VCO pilot 2| completely fills the chambers I3, I4, I5, I8 and returns to the operating liquid supply system through drain conduit |3b. Thus all moving parts operate submerged in lubricating oil.

The integrated operation of this servo-mechanism may be outlined as follows.

Assume first that the powei'plant is shut down, which means, of course, that there will be no compressor discharge pressure in the bellows 58, and no hydraulic motive uid supplied to the CCO supply conduit 9a. Therefore, the flexible bellows 58 will be collapsed by the compression spring 68, so that pilot 84 is in its lowermost position with land 84a below the port 11 and land 84h below the drain port 18. Without CCO pressure, the VCO piston 23 will also occupy its lowermost position, as shown in Figure l, by reason of the downward biasing force of the main-spring 32. Finally, the fuel rate selecting cam 34 will be in its maximum clockwise position, with cam follower 83 in maximum elevated position and lever 8| occupying the position shown in the drawing.

If now the powerplant is started and the fuel rate selecting cam 84 is caused to rotate counterclockwise, the cam follower roller 83 will descend, lever 8| will pivot clockwise about the abutment roller 88, with the result that pivot 82 causes VCO pilot spindle 31 to descend, admitting oil to the VCO chamber I9, and by way of passages 30, 3| to the pressure chamber 29 in VCO piston 23. Increasing pressure in chamber 29 causes piston 23 to rise against the bias of spring 32, thus causing lever 81 to pivot counterclockwise about pivot 88, so that roller 88 causes the left-hand end of lever 8| to rise. This motion restores pilot 31 to the aligned condition, in which the lower land 31h blocks off the CCO inlet port 45. It follows that, as cam 84 continues to rotate counterclockwise, the VCO pilot 31 will be positioned to establish an increasing VCO pressure in the chamber 29, piston 23 being progressively positioned upwardly as the VCO pressure increases. Thus it will be seen that there will be a preselected VCO pressure corresponding to a preselected position of piston 23 ior cach angular position of the input cam 84.

Meanwhile, the CCO pressure supplied to the compensator servo 2.2b has entered the upper chamber 'i0 and forced piston 85 downwardly to its lowermost position, corresponding to the completely collapsed condition of pressure responsive bellows 58. This causes the abutment roller 88 to be positioned to its extreme righthand condition, as shown in full lines at 88, so that the maximum degree of compensating effect is introduced. Then, as the high pressure compressor inlet pressure rises into the normal operating range, increasing pressure in bellows 58 causes the hydraulic amplifier 22h to effect progressive positioning of lever 84 counterclockwise about pivot 95 so that the abutment roller 88 is positioned progressively to the leit, meaning that the degree of the compensating elect introduced progressively changes.

Once the machine is operating in its normal range, it will be seen that any change in the high pressure compressor inlet pressure, due to changes in speed of the low pressure compressor I, will be accompanied by a change in the position of the abutment roller 85 so as to appropriately modify the follow-up action of the VCO pislpn 23 on lever 8|.

The net eiiect of the above-described method of operation may be seen graphically in Fig. 2. Here the abscissa represents rotational displacement of the input cam 84 from the minimum or off position shown in Fig. l to its maximum counterclockwise position corresponding to the maximum position of handle 85a. The ordinate represents the VCO signal pressure communicated from port I9 by way of conduit 1b to the hydraulic servo 1a of the fuel pump. As noted on the curves in Fig. 2, the lowei curve represents the performance of the apparatus with the abutment roller 88 in the full line position 86 shown in Fig. 2, while the upper curve represents the performance with the abutment roller in the dotted line position 88a, directly over the VCO piston 23. Actually, these curves are not curved at all but are straight lines, the contour of the input cam 84 being so chosen that straight-line performance curves will result. This maires it easier to design the fuel system and the fuel pump control servo 1a.

Thus, it will be seen that shifting the abutment roller 86 a comparatively small distance has a very substantial effect on the operating characteristics of the combination.

The invention makes it possible to so design the regulating mechanism that a preselected fuel-air ratio is obtained for any given position of the input cam 84, regardless of variations in the operating speed of the low pressure compressor I. This means that, for each position of input cam 84, there will be a preselected rate of fuel supply which is properly proportioned to the weight fiow of air to the combustion system, irrespective of any variations which may occur in the speed of the independently driven low pressure compressor l.

It will be obvious to those acquainted with the art that many modilications and substitutions of mechanical equivalents may be made. For instance, the hydraulic amplifier 22D might be replaced by any suitable means for positioning the compensating lever 94 as a function of high pressure compressor inlet pressure. Also, it may be noted that the compressor pressure signal may be derived from the conduit 5 anywhere between the discharge end of the low pressure compressor and the inlet casing of the high pressure compressor. It will be obvious that the mechanical details of the VCO piston, and of the VCO pilot, and the linkage interconnesting them may also take many other forms. It is of course intended to cover by the appended claims all such modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In hydraulic servo-mechanism, the combination of a housing, a first reciprocable piston member having a cylindrical chamber in one end thereof and containing a second non-reciprocable piston member deiining With the slidable piston a pressure chamber, the second piston having a. passageway for communicating liquid to said chamber, a main coil spring surrounding the first piston and having an end portion engaging the piston to exert a force thereon in opposition to the pressure'in said chamber, a source of operating liquid at substantially constant pressure, pilot valve means for supplying liquid from said source to said passageway and including a pilot spindle disposed for longitudinal sliding movement in a direction substantially parallel to the axis of said pistons, linkage means connecting the first piston to position said pilot spindle including a iirst lever member disposed generally normal to the exis of the piston and pilot and having an intermediate portion connected to position the pilot spindle, an input member engaging the end of the lever remote from the first piston, and variable abutment means interposed between the other end of the lever and the first piston, said abutment means comprising a slider member adapted to be positioned linearly in a direction generally parallel to the lever, and a second lever member pivoted at one'end to said slider and having a mid-portion engaged by the end of the first piston, the other end of said second lever having a member engaging the adjacent end portion of the first lever, and means for positioning said slider towards and away from the first piston to vary the position at which said second lever end portion engages the first lever relative to the axis of the piston.

2. Hydraulic servo-mechanism in accordance with claim l in which the means for positioning the slider comprises a pressure signal responsive bellows connected to a pilot spindle, the pilot spindle being slidably disposed in a double-acting hydraulic servo-piston member With ports controlled by the pilot spindle and passages for supplying operating liquid to either side of the piston alternately, and lever means connecting said servo-piston with the slider whereby the latter is positioned in accordance With said pressure signal.

NEAL E. STARKEY.

References Cited in the lile of this patent UNITED STATES PATENTS

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