US2713351A - Restoring linkage for hydraulic servomechanism of turbine valve gear - Google Patents

Description

July 19, 1955 VAN NEST 2,713,351

RESTQRING LINKAGE FOR HYDRAULIC SERVO-MECHANISM OF TURBINE VALVE GEAR Filed June 26, 1952 Inventor-: Fvancis HVan Nest,

His Attor-nea.

United States Patent RESTORING LINKAGE FOR HYDRAULIC SERVO- MECHANISM OF TURBINE VALVE GEAR Francis H. Van Nest, Marblehead, Mass., assignor to General Electric Company, a corporation of New York Application June 26, 1952, Serial No. 295,635

7 Claims. (Cl. 137--630.19)

This invention relates to hydraulic servo-mechanism, particularly to hydraulic motor arrangements for actuating the inlet valves of an elastic fluid turbine. The invention is specifically concerned with an improved linkage for feeding back a restoring movement to the hydraulic pilot valve.

One well-known type of steam turbine valve gear is that referred to as the bar-lift type. This comprises a plurality of flow control valve disc members having stems of different lengths slidably disposed through a horizontal lift bar connected to be positioned by a pair of lift rods. A suitable hydraulic motor exerts tension on the lift rods to position the lift bar upwardly so as to engage the valve stems in a preselected sequence and admit operating fluid to the respective sections of the first stage nozzles. The hydraulic motor is controlled by a pilot valve positioned by a speed-responsive device, as modified by other components of the turbine regulating mechanism. Heretofore, the restoring movement for repositioning the pilot valve to discontinue the movement of the hydraulic motor when the turbine valves have moved far enough has been obtained through a linkage connecting the pilot valve with the piston rod of the hydraulic motor. Thus, as soon as the hydraulic motor piston begins to move, a restoring movement is fed back to the pilot valve. Such arrangements have sometimes been found unsatisfactory in comparatively large turbines because the very great forces imposed on the valve lift rods, as the respective valve discs begin to open, produce bending deflections in the levers connecting the lift rods with the piston rod of the hydraulic motor. Such bending deflections mean that the piston can move a certain distance without producing a corresponding movement of the turbine valves. This introduces a source of inac curacy in the turbine governing function, the magnitude of which can be sufiiciently serious as to make the turbine unfit for applications such as driving paper or textile mills where the speed must be held very accurately.

Accordingly, the object of the present invention is to provide an improved follow-up restoring linkage arrangement for turbine valve gear of the bar-lift type specially constructed and arranged so that the follow-up movement is communicated to the pilot valve in more exact response to the movement of the turbine inlet valves.

A further object is to provide an improved turbine valve gear of the type described in which the mechanical components of the linkage connecting the hydraulic motor with the valves can be made lighter, since any bending deflections occurring therein have little or no effect on the accuracy of speed control.

A still further object is to provide improved turbine valve gear of the bar-lift type which is substantially of no greater cost or complexity than those formerly used, yet achieving a substantial improvement in the degree of accuracy of the speed-governing function obtained.

Other objects and advantages will become apparent from the following description taken in connection with the accompanying drawing in which the single figure rep- 2,713,351 Patented July 19, 1955 resents diagrammatically a steam turbine having valve gear of the bar-lift type actuated by a hydraulic motor incorporating an improved restoring linkage arranged in accordance with the invention.

Generally stated, the invention is practiced by effecting the restoring movement by a linkage connected directly to the valve lift rods themselves, as compared with the prior art devices in which the restoring movement was effected from the piston rod of the hydraulic motor.

Referring now more particularly to the drawing, the elastic fluid turbine is indicated only diagrammatically at 1 as having a steam inlet chest 2, to which motive fluid is admitted through an inlet conduit 2a. Motive fluid from the steam inlet chamber 2b is admitted to the i respective sections of the first-stage nozzles 2c through a plurality of ports 3, the flow through which is controlled by a row of disc members 4 each having short valve stem rods loosely disposed through spaced openings in the valve lift bar 5, and having abutment members 4a.

" As will be understood by those acquainted with the barlift type of valve gear, the stems are of different lengths so that the discs 4 are picked up in a predetermined sequence as the lift bar 5 rises and engages the members 4a.

Such bar-lift turbine valve gear arrangements are disclosed, for instance, in the copending application of S. Jacobs and W. E. Gleason, Serial No. 263,352, filed December 26, 1951, and the patent of F. H. Van Nest and L. B. Wales, No. 2,613,542, issued October 14, 1952, both assigned to the same assignee as the present application. The mechanical details of such valve arrangements are not necessary to an understanding of the present invention, and it is necessary only to note here that, as the lift-bar 5 rises, the members 4a carried at the upper end of the valve stems engage the top surface of the lift bar so that the discs 4 are caused to rise in a preselected sequence.

The lift-bar 5 is positioned by a pair of tension liftrods 6, 7 disposed through suitable guide bushings (not shown) in the top wall of the valve inlet chest. A pair of pivoted links 8, 9 connect the lift-rods with a main operating lever indicated generally at 10. This lever is actually a V-shaped frame having one leg pivoted at 11 to a stationary fulcrum, the other leg being pivoted at 12 to a second spaced fixed fulcrum. Link 8 is pivoted at 8a to the lever leg 10a, and link 9 is pivoted at 9a to the lever leg 10b. The vertex of the V-lever is pivoted at 13 to the end of the hydraulic motor piston rod 14.

The hydraulic actuating motor indicated generally at 15 comprises a cylinder having a single-acting piston 16 biased downwardly by a heavy coil spring 17. Hydraulic operating liquid is supplied to cylinder 15 so as to move the piston 16 upwardly against the bias of coil spring 17, as controlled by a hydraulic pilot valve indicated generally at 18. This pilot comprises a bush-ing member having a bore in which the pilot 19 is longitudinally slidable. The spaced lands 19a, 19b of pilot 19 define an inlet chamber 20 to which operating liquid at a suitable pressure is supplied by way of an inlet conduit 21. It will be appreciated by those familiar with turbine governing systems that this hydraulic operating liquid will ordinarily be supplied by a suitable pump driven from the turbine shaft (not shown).

The upper pilot land 1% is normally aligned with a port 22 from which conduit 23 supplies operating liquid to the motor 15. Any liquid leaking past the piston 16 is drained by way of a conduit 24. It will be understood by those familiar with hydraulic servo-mechanism that upward movement of pilot 19 causes operating liquid from chamber 20 to be admitted to port 22 and by way of conduit 23 to the motor 15 so that piston 16 moves upwardly against the spring 17 Conversely, downward movement 3 of pilot 19b uncovers the port 22 so that operating liquid from motor 15 drains through conduit 23 and out the top of the pilot bushing by way of the drain conduit 25.

Pilot 19 is arranged to be positioned by a speed-responsive regulator, indicated diagrammatically as being a flyball governor 26 driven at a speed proportional to that of the turbine rotor by suitable gearing (not shown), arranged to pull downwardly on a pivot 27 when speed in creases, and to push upwardly when speed decreases. Pivot 27 is connected to the mid-portion of a floating lever member 28 having its righthand end pivoted at 28a to the pilot rod 190, and at its lefthand end at 28b to a link 29 connected to an intermediate lever 35) carried on a fixed fulcrum 31. The lefthand end of lever 39 is connected by a link 32 to a specially arranged feed-back or restoring lever indicated generally at 33. The lever member 33 is actually a 3-legged member having a first lever arm portion 33a projecting transversely adjacent the lift-rod 6, a second similar lever arm member 33]) projecting adjacent the liftrod 7, and a third output lever arm portion 330 the end of which is pivoted at 34- to the link 32. These three lever portions are rigidly secured to a torque tube member 3311 supported in suitable journals 35, 36.

The lever portions 33a, 3317, are not positively secured to the lift-rods 6, 7, but are connected to be positioned thereby by a lost-motion or break-away connection, as follows. The liftrod 6 carries a movable abutment 6a to which is connected a coil spring 37 the other end of which is connected to the end portion 38 of lever 33a. Lift-rod 6 also carries a transversely extending abutment member which may be in the form of a round pin 39. Ordinarily, spring 37 biases lever 33a in a clockwise direction so that lever portion 38 is held in contact with the abutment 39.

Likewise, the lift-rod 7 has a first abutment member 40 with a coil spring 41 connected to a lever end portion 42 of the lever arm 33b. Spring 41 biases the lever end portion 42 into engagement with a second abutment 43 carried by the lift-rod 7.

It will be apparent that clockwise rotation of the lever member 33 will cause pivot 34 to rotate the intermediate lever 3-9 counterclockwise about fulcrum 31, so that pivot 28b is caused to rise, thus causing floating lever 28 to move clockwise about pivot 27, so that the pilot rod spindle 19c is lowered. counterclockwise rotation of the lever t member 33, of course, moves these elements in the opposite sense.

The operation of this improved pilot restoring mechanism will be seen from the following.

When the plant is shut down, spring 17 biases piston 16 .1

to the bottom of its stroke, so that the lift-bar 5 is in its lowermost position with all of the valve discs 4 seated on the inlet ports 3. in this condition, the abutments 39, 43 associated with lift-rods 6, 7, respectively, positively engage the lever end portions 38, 42 so that lever member 33 is rotated to its extreme counterclockwise position. Therefore, the pivot 27 associated with speed governor 26 will be in its uppermost position, pivot 28b will be in its lowermost position, so that the pilot 19 will be raised to put the inlet conduit 21 in open communication with the motor 15. if, now, the turbine is started and hydraulic operating liquid supplied to conduit 21, the resulting pressure in hydraulic motor 15 will cause piston 16 to rise, so that lever member 10 moves counterclockwise about the pivots 11, 12. thus raising the lift-rods 6, 7 to'position the lift-bar 5 upwardly.

Assume now that the turbine is in operation and the load on the turbine'is such as to require the second and third valves 4 (counting from the left end in the drawing) to be essentially wide open. If now the output of the turbine is increased so that the fourth valve is picked up by the lift bar, then most of the force required to lift this valve will be imposed on the righthand lift rod 7. Under such conditions, the other lift rod 6, which is more lightly loaded, will follow very closely the movement of the hydraulic piston 16. On the other hand, a greater movement of piston 16 will be required in order to overcome the bending deflections in the operating lever 1017 before the hydraulic motor exerts sufficient force on lift rod 7 to cause the fourth valve to move from its seat. Meanwhile, the abutmcnt member 39 will have moved away from the lever portion 33a, with lever 33c remaining stationary. When lift rod 7 finally begins to move upwardly, the abutment 43 permits lever 33b to pivot clockwise, whereupon lever arm 33c moves downwardly to restore the pilot valve 19. Thus it will be seen that the pilot valve is not restored to neutral position until the more heavily loaded lift rod 7 has moved the required distance.

Likewise, when the first valve (counting from the left end of lift bar 5) is opened, the abutment 43 of the more lightly loaded lift-rod 7 will move away from lever 33b, and movement of the other abutment 39 will produce the restoring effect on the pilot valve.

When the load on the turbine is decreased, requiring the closing of some or all of the valves, the relative loading on the lift rods 6, 7 will vary, depending on the location of the valve which is being closed at the moment. In each case, however, the abutment associated with the more heavily loaded lift rod will be the one which controls the restoring effect on the pilot valve.

In other words, the net effect of the arrangement is that, in the event the lift-rods 6, 7 are not equally loaded, the follow-up motion will not be communicated back to the pilot 19 by way of the lever 33, link 32, and levers 3t), 28, etc., until the more heavily loaded of the two lift-rods begins to move. This is equivalent to saying that the follow-up effect is produced on the pilot valve as a function of movement of whichever lift rod is farthest out-of-phase with the motion of the hydraulic motor. This insures that movement of the lift-bar 5 will be accurately effected by the hydraulic motor 15 irrespective of unequal loading on the lift bar, and unaffected by bending deflections in the lever 10 and other members which may experience some lost motion or bending.

Thus, it will be seen that the parts of the linkage, particularly the comparatively heavy V-lever 10, may be made substantially lighter than in conventional valve gear where the parts must be reinforced sufficiently to prevent such bending deflections as might introduce errors into the action of the hydraulic servomcchanism. The result is a substantial improvement in the weight and cost characteristics of the machine, without materially increasing the complexity of the linkage. The invention makes possible the application of the comparatively inexpensive and foolproof barlift type of valve gear to turbines for use where the speed must be very accurately maintained.

While only one embodiment of the invention has been disclosed specifically, and that in very diagrammatic form, it will be obvious to those familiar with the art that many changes and substitutions of mechanical equavalents may be made. For instance, while the speed governor 26 has been shown as acting directly on the floating lever 28, in an actual machine there will ordinarily be a hydraulic relay with a pilot valve positioned by the fly-ball governor 26 and a power piston controlled by the pilot for positioning the pivot 27. Such arrangements are well-known in the turbine art and the mechanical details thereof need not be described more particularly here. It will be obvious that the linkage connecting the pilot 19, speed governor 26, and feed-back lever 33 may take many forms. The precise details of the lost motion or break-away connection between the lever arms 33a, 33b and the lift-rods 6, 7 may also vary considerably.

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 valve gear for an elastic fluid turbine including a lift-bar member for positioning the turbine inlet valves, the combination of a pair of parallel spaced tension rods connected to pull the bar in the valve-opening direction, a main operating lever member having spaced legs with portions supported on fixed fulcrums and other spaced portions thereof connected to the respective tension rods, motor means with an output member connected to said lever member for positioning it in the valve-opening direction, pilot means for controlling the operation of said motor, and restoring linkage means independent of the force-transmitting members which connect the motor means to the tension rods, said linkage means being connected with said pilot means and tension rods to reposition the pilot means only in accordance with movement of the tension rods and independently of bending deflections and lost motion occurring in said force-transmitting members.

2. In valve gear for an elastic fluid turbine including a lift bar member for positioning the turbine inlet valves, the combination of a pair of parallel spaced tension rods connected to the bar for moving it in the valve-opening direction, a main V-lever member hav ing spaced legs with portions supported on fixed fulcrums and spaced portions thereof connected to the respective tension rods, a hydraulic motor with an output member connected to the V-lever member for positioning it in the valve-opening direction, a pilot valve for controlling the flow of operating liquid to said motor including a slidable pilot spindle member, and feedback ]inkage means independent of the force-transmitting members which connect the motor means to the tension rods, said linkage means being connected with said spindle and tension rods to reposition the pilot spindle only in accordance with movements of the tension rods and independently of bending deflections and lost motion in the force-transmitting members connecting the hydraulic motor to the tension rods.

3. In valve gear for an elastic fluid turbine including a lift-bar member for positioning the turbine inlet valves, the combination of a pair of parallel spaced lift-rods connected to the lift-bar for moving it in the valve-opening direction, a main operating lever member having spaced leg portions supported on fixed fulcrums with intermediate portions thereof connected to the respective liftrods, a hydraulic motor with an output member connected to position said main operating lever in the valveopening direction, a pilot valve adapted to control the flow of operating liquid to said motor and including a longitudinally slidable pilot spindle member, and linkage means for positioning said pilot spindle directly from the valve lift rods, said linkage including a feed-back lever member having a pair of spaced arms transversely disposed adjacent the respective lift-rods, and a breakaway connection between said arms and the lift-rods whereby the feedback lever is caused to move in the valveopening direction only when both lift-rods become displaced.

4. In valve gear for an elastic fluid turbine including a lift-bar member for positioning a plurality of turbine inlet valves, the combination of a pair of parallel spaced lift-rods connected to move the lift bar in the valve-opening direction, a main operating lever member having spaced leg portions supported on fixed fulcrums with other portions thereof connected to the respective lift-rods, motor means with an output member adapted to position said main operating lever in the valve-opening direction, pilot means connected to control said motor, and linkage means for positioning said pilot directly from the lift rods, said linkage including a restoring lever member having a pair of members disposed adjacent the respective 6 lift-rods, and break-away means connecting each of said members with its associated lift-rod, whereby the restoring lever member effects movement of the pilot in accordance with motion of Whichever lift-rod is farthest out of phase with the motion of the hydraulic motor.

5. In valve gear for an elastic fluid turbine including a lift-bar member for positioning the turbine inlet valves, the combination of a pair of parallel spaced lift-rods connected to move the lift bar in the valve-opening direction, a main V-lever member having spaced legs with portions supported on fixed fulcrums and other spaced portions thereof connected to the respective lift rods, a hydraulic motor with an output member connected to position said V-lever in the valve-opening direction, a pilot valve adapted to control the flow of operating liquid to said motor and including a longitudinally slidable pilot spindle member, and restoring linkage means for repositioning the pilot spindle in accordance with movement of the lift rods, said restoring linkage including a feed-back lever member supported on a fulcrum adjacent the lift rods and having a pair of spaced lever arms disposed substantially transverse to the lift rods and break-away means connecting the lever-arms to the respective lift rods, said connecting means each including an abutment member on the lift rod adapted to engage the lever arm to limit rotation thereof in at least one direction and spring means biasing the lever arm to elfect engagement thereof with said abutment, whereby the feed-back lever is caused to move to reposition the pilot spindle only when the more heavily loaded lift rod becomes displaced.

6. In hydraulic servo-mechanism for positioning a pair of parallel spaced load-carrying rod members each adapted to move longitudinally, a main operating lever member having spaced leg portions disposed substantially normal to said rod members, each of said leg portions being supported on a fixed fulcrum with a spaced portion thereof connected to said respective rod members, a hydraulic motor with an output member connected to position said main operating lever, a pilot valve adapted to control the flow of operating liquid to said motor and including a longitudinally slidable pilot spindle member, and follow-up linkage means for repositioning the spindle directly from said load carrying rod members including a feed-back lever member with a pair of spaced arms disposed transversely adjacent the respective rod members, and a break-away connection between said arms and rods whereby the feed-back lever is caused to move only when the hydraulic motor effects displacement of both load carrying members.

7. In servo-mechanism for positioning a pair of parallel spaced load-carrying rod members each adapted to move longitudinally, a main operating lever member having spaced leg portions disposed generally transverse to the rod members, said leg portions being supported on fixed fulcrums with spaced portions thereof connected to move said respective rod members against the resistance of the load thereon, motor means with an output member connected to position said main operating lever, pilot means connected to control said motor, and restoring linkage means for repositioning the pilot directly from said load carrying rod members and including a restoring lever member with a pair of arm members disposed adjacent the respective rod members, and break-away connections between said respective arms and rods whereby the restoring lever is caused to reposition the pilot in accordance with movement of that rod which is farthest out of phase with the movement of the motor.

References Cited in the file of this patent UNITED STATES PATENTS 801,399 Rice Oct. 10, 1905 2,304,993 Franck Dec. 15, 1942 2,596,242 Hill May 13, 1952

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