US3625241A

US3625241A - Steam admission valve structure for steam turbines

Info

Publication number: US3625241A
Authority: US
Inventors: James Rodger Shields
Original assignee: Carrier Corp
Current assignee: Carrier Corp; Elliott Turbomachinery Co Inc
Priority date: 1969-10-16
Filing date: 1969-10-16
Publication date: 1971-12-07
Anticipated expiration: 1988-12-07

Abstract

The valves are moved toward and from the seats by a valve lift bar provided with removable split bushing in which the valve stems are slidable. The stems are formed with enlarged integral head portions dimensioned to pass through the apertures in the bar in which the bushings are mounted. The heads are engaged by the bushings upon upward movement of the bar. Means is provided for proper vertical adjustment of the bushings in the bar to cause sequential movement of the valves form their seats upon upward movement of the lift bar.

Description

United States Patent James Rodger Shields Pittsburgh, Pa. 867,017

Oct. 16, 1969 Dec. 7, 197 1 Carrier Corporation Syracuse, N.Y.

[ 72] Inventor [21 Appl. No. [22] Filed [45] Patented [73] Assignee [54] STEAM ADMISSION VALVE STRUCTURE FOR STEAM TURBINES 2 Claims, 4 Drawing Figs. [52] U.S. Cl l37/630J9, 137/501, 251/77 [51] lnt.Cl Fl6k l/00, F16k 31/44 [50] Field of Search ..137/630.16, 630.19, 635; 251/77; 308/4 R, 5 V [56] References Cited UNITED STATES PATENTS 2,385,537 9/1945 Pentheny... 137/630. 19

2,790,453 4/1957 Maloney 251/77 X 2,830,620 4/1958 Shuptrine 137/630. 19

2,777,466 H1957 Ericson l37/630.l9 FOREIGN PATENTS 505,425 8/1930 Germany 308/4 Primary E.raminer Robert G. Nilson Attorneys-Harry G. Martin, Jr. and .1. Raymond Curtin ABSTRACT: The valves are moved toward and from the seats by a valve lift bar provided with removable split bushing in which the valve stems are slidable. The stems are formed with enlarged integral head portions dimensioned to pass through the apertures in the bar in which the bushings are mounted, The heads are engaged by the bushings upon upward movement of the bar. Means is provided for proper vertical adjustment of the bushings in the bar to cause sequential movement of the valves form their seats upon upward movement of the lift bar.

PATENTED DEC 7 I97! SHEET 1 [IF 2 INVENTOR. J. RODGER SHIE) 05 BY ATTORNEY PATENTEDDEC nan SHEET 2 [IF 2 BACKGROUND OF THE INVENTION Different valve arrangements are used to control the admission of steam into steam turbines. In one arrangement, the bottom wall of the steam chest is formed with a plurality of steam passages. A precision machined seat is mounted in each passage. A valve is movable vertically into and out of engagement with each seat to control the admission of steam from the steam chest through the passages, each of which is connected to a group of first stage nozzles.

As the demand load on the turbine increases, the valves are moved upwardly from their seats in a predetermined sequential order by a valve lift bar which is mounted above the series of seats for movement toward and from the same. The lift bar is formed with an aperture vertically aligned with each valve seat. Each valve has a stem that extends upwardly through an aperture and is slidable in the aperture. The upper end portions of the valve stems are threaded to receive stop nuts. When the lift bar is moved upwardly, it engages the stop nuts on the valve stems, and moves the valves upwardly from the seats. The sequence in which the valves are moved from their seats and the extent of such movement is determined by the position of the stop nut on each valve stem, and jam nuts are provided to lock the stop nuts in adjusted position.

The lift valve is reciprocated vertically by a servomotor which is controlled by a governor, whereby the valves are opened and closed sequentially according to the load demand on the turbine. The sequential, rather than simultaneous, operation is employed-to provide for the admission of steam to select groups of nozzles in a predetermined order for more efficient turbine operation and for better balance with minimum vibration. Accordingly, upon initial upward movement of the lift bar, a valve having stop nuts adjusted close to the lift bar will be first moved to open position. The valve of the series having the stop nuts on its stem adjusted to a higher position will open upon further upward movement of the lift bar, and so on. With the lift bar in its uppermost position, all of the valves are open, and as the lift bar is moved downwardly, the valves are closed in reverse sequential order.

Due to the high velocity of the steam, and turbulence thereof in the steam chest, vibration of substantial magnitude is set up and is imparted to the valve gear. The threaded end portions of the valve stems create areas where fatigue failure develops, which on occasion results in fracture of the valve stem. Such an occurrence creates a serious problem. Obviously, a valve with a broken stem is inoperable and the speed and performance of the turbine can no longer be controlled with accuracy, and in some cases not at all. Also, there is the great danger that the broken end of a stem, and/or the stem nuts, may pass through the valve seat and through the nozzles and be ingested in the blades of the turbine rotor, necessitating an expensive repair job.

This invention has as an object a steam admission valve arrangement of the lift bar type, embodying a structural arrangement by which fatigue failure is reduced to a minimum, if not entirely eliminated, and the danger of components of the valve gear being ingested in the turbine is substantially eliminated.

SUMMARY OF THE INVENTION The steam admission valves are lifted from their seats by a valve lift bar provided with removable split bushings through which the valve stems extend. The upper ends of the stems have enlarged integral heads dimensioned to pass through the apertures in the lift bar in which the bushings are mounted, but are engaged by the bushings when the bar is moved upwardly. Each bushing is formed at its upper end with a radial flange. The bushings are adjusted vertically by the use of annular shims placed between the flange of the bushing and the bottom of the counterbore in the aperture in the lift bar.

2 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of the upper portion of a turbine steam chest including a valve structure embodying my invention, the lift bar and valves being shown in elevation;

FIG. 2 is an enlarged sectional view of the left end portion of the structure shown in FIG. 1;

FIG. 3 is a sectional view of the lift bar, a pair of valves, and valve seats, the valve stems being provided with conventional adjusting nuts; and

FIG. 4 is an enlarged sectional view illustrating a modified form of bushing.

DESCRIPTION OF THE PREFERRED EMBODIMENT I0 designates a steam chest having a steam inlet 11 and a bottom wall 12. The chest is provided with a cover 13 formed with upwardly extending brackets 14 in which there is journaled a valve-actuating shaft 15.

The cover is also formed with hubs l7 apertured to slidably receive lift bar actuating rods 20, the upper ends of which are pivotally connected to arms 23 fixed to the shaft 15, the connection being by way of clevis 25.

The bottom wall I2 of the steam chest is formed with a linear series of passages in each of which there is mounted a valve seat 27. Valve lift bar 30 is attached to the actuating rods 20 and is arranged above the valve seats 27. The lift bar is formed with an aperture in vertical alignment with each valve seat 27.

A split bushing 33 is positioned in each aperture in the lift bar 30. The upper portions of the apertures in the lift bar are counterbored or otherwise enlarged to form shoulders 35 spaced downwardly from the top side of the bar. Each bushing 33 is formed with a radially extending flange 40 spaced upwardly from the lower end of the bushing.

The valves 41 are formed with stems 42. The upper ends of the stems are formed with integral enlarged heads 43 which are dimensioned for insertion through the apertures in the bar 30. With the valve stems inserted through the apertures in the lift bar, the split bushings are positioned about the valve stems 42 and are moved downwardly into the apertures with the flanges 40 engaging the shoulders 35.

The bushings 33 are retained against upward vertical displacement from the bar 30 by retaining means. In the arrangement disclosed, the counterbores are formed adjacent their upper ends with circumferentially extending grooves for the reception of snaprings 47 which extend inwardly over the flanges 40. However, it will be apparent that other forms of retaining means may be used.

The lift bar 30 is moved upwardly upon oscillation of the shaft 15 which is brought about by operation of a servomotor under the control of the turbine governor. This motor effects vertical movement of the length 50, the upper end of which is connected to an arm 51 fixed to the shaft 15. As previously stated, the valves 41 are moved upwardly from the seats 27 successively in a predetermined sequence. For example, the numbers appearing below the valves in FIG. 1 illustrate one sequential operation, the valve at the center of the series being the first to open, and the adjacent valve to the left being the second to open in the series, and so on as indicated by the numerals 1 to 7.

Preferably, the operation is such that the second valve to be opened does not begin to open until the steam ring pressure on the nozzle or group of nozzles supplied by the first valve has built up to a point slightly below throttle pressure. Similarly, each succeeding valve does not begin to open until the ring pressure on the preceding nozzle group has built up to approximately throttle pressure. The pressure established by the operation of each valve is determined in part by the position of the lift bar 30 as each bar is engaged. In other words, it depends on how far the lift bar travels upwardly after it has engaged and started to move a valve. It is therefore necessary that the lift bar successively engages the valves in accordance with the selected sequence and at a relatively precise position of the bar.

In the arrangement of my invention, the enlarged head portions 43 of the valves are engaged by the bushings 33. in order to effect engagement of each valve head 43 at the proper instant, means is provided for adjusting the bushings 33 axially in the bar 30. The distance between the shoulders 35 and the retaining rings 47 is substantially greater than the axial dimension of the flanges 40. Accordingly, spacing shims 53 are positioned between the shoulders 35 and the flanges 40 and/or between the flanges 40 and the retaining rings 47. With this arrangement, the bushings 33 are adjusted axially in the bar 30 over a large range commensurate with the difference between the thickness of the flanges 40 and the spacing of the shoulders 35 and retaining rings 47.

As illustrated in FIG. 4, the bushings 33 may be dimensioned to extend a considerable distance upwardly from the flanges 40. With this arrangement, different lengths of bushings can be employed, permitting the valves 41 to be of like dimension. in other words, by making the bushings of different axial length, it is not necessary to make the valve stems of difierent axial length.

The construction presently employed is illustrated in FIG. 3 wherein the upper ends of the valve stems are threaded to receive adjusting nuts 60. These nuts are adjusted axially on the valve stems to provide for proper engagement of the lift bar 30 with each valve to effect opening of the valves in the proper sequence. As previously stated, vibration imparted into the valve stems during operation of the turbine develops fatigue in the threaded end portions of the valve stems and, on occasion, the stems fracture.

it will be apparent that with my invention, the likelihood of fatigue failure occurring in a valve stem has been reduced to a minimum, and, also, the hazard of components of the structure being ingested in the turbine has been eliminated.

lclaim:

l. A steam admission valve structure for steam turbines comprising a fixed member formed with plurality of passages disposed vertically and arranged in side-by-side relation, each of said passages being provided at its upper end with a valve seat, a one piece valve lift bar mounted above said seats for movement toward and from the same, said bar being formed with an aperture axially aligned with each of said valve seats, a split bushing mounted in each of said apertures, retaining means detachably mounted in each of said apertures for fixing each of said bushings against axial movement relative to said bar, a valve cooperable with each of said seats, each of said valves having a stem extending through one of said bushings and being slidable therein, each of said valve stems being formed with an integral enlarged head portion, and said head portions being dimensioned for passage through said apertures and engageable by the bushings upon upward movement of said lift bar, each of said apertures being formed with a shoulder spaced downwardly from said retaining means, each of said bushings being formed with a radially extending flange positioned intermediate to said shoulder and said retaining means, said retaining means being positioned upwardly from said shoulders a distance exceeding the axial thickness of said flanges, a plurality of annular shim members encircling each of said bushings, said shims in conjunction with said flanges filling the spaces between said shoulders and said retaining means and means operable to effect vertical reciprocation of said lift bar to move said valves into and out of engagement with said seats.

2. A valve structure as set forth in claim I, wherein said retaining means consist of a snapring positioned in each of said apertures upwardly from said shoulders.

Claims

1. A steam admission valve structure for steam turbines comprising a fixed member formed with a plurality of passages disposed vertically and arranged in side-by-side relation, each of said passages being provided at its upper end with a valve seat, a one piece valve lift bar mounted above said seats for movement toward and from the same, said bar being formed with an aperture axially aligned with each of said valve seats, a split bushing mounted in each of said apertures, retaining means detachably mounted in each of said apertures for fixing each of said bushings against axial movement relative to said bar, a valve cooperable with each of said seats, each of said valves having a stem extending through one of said bushings and being slidable therein, each of said valve stems being formed with an integral enlarged head portion, and said head portions being dimensioned for passage through said apertures and engageable by the bushings upon upward movement of said lift bar, each of said apertures being formed with a shoulder spaced downwardly from said retaining means, each of said bushings being formed with a radially extending flange positioned intermediate to said shoulder and said retaining means, said retaining means being positioned upwardly from said shoulders a distance exceeding the axial thickness of said flanges, a plurality of annular shim members encircling each of said bushings, said shims in conjunction with said flanges filling the spaces between said shoulders and said retaining means and means operable to effect vertical reciprocation of said lift bar to move said valves into and out of engagement with said seats.

2. A valve structure as set forth in claim 1, wherein said retaining means consist of a snapring positioned in each of said apertures upwardly from said shoulders.