FIELD OF INVENTION
This invention generally relates to an improved design of pivot ring used for Francis type hydro turbines having facility for bottom removal of runner. More particularly, the invention relates to a feature in the new design for adjusting the guide vane passage height, feature to centralize the labyrinth and lock it without dowelling and an arrangement to support the pivot ring at the inner overhanging end.
BACKGROUND OF THE INVENTION
In a typical Francis type hydro turbine a pivot ring is a major item of the guide apparatus and has the following functions:-
1. It houses the pivot of the guide vane about which the guide vane (8) rotates i.e., the lower bush of the guide vane and forms passage for guide vane in conjunction with top cover.
2. It houses the lower labyrinth in which the runner rotates in a fine clearance.
The pivot ring is bolted to a stay ring on its upper outer end. At its lower inner end it is connected to a draft tube cone. In the turbines having no facility for bottom removal of the runner, the pivot ring and the draft tube cone are

embedded in concrete. However, in Francis turbines which have a feature for bottom removal of the runner, the pivot ring including the draft tube cone are not embedded in concrete and thus, can be dismantled i.e. they can be removed from the bottom of turbine. The pivot ring and the draft tube cone are thus exposed.
In these turbines which do not have provision for bottom removal of runner, the pivot ring is fixed to the stay ring without any provision for adjustment of the guide vane passage height.
In a conventional turbine, a part of the downward hydraulic load on pivot ring is shared by the concrete. However, for a pivot ring of a turbine having facility for bottom removal of the runner, the pivot ring hangs from the stay ring. Due to hydraulic load acting on the pivot ring, the pivot ring deflects downwards which in-turn engulf the clearances of the guide vane stem and the bush and may sometimes seize the smooth movement of guide vanes. To limit the deflection of the pivot ring to a value which is within the running clearances between the guide vane stem/bush, the pivot ring has to be made very rigid which however, increases the weight and cost of the pivot ring exorbitantly. Also, the pivot ring suspended from the stay ring and free at its lower end is prone to vibration and thus quite often leading to failure of the bolts joining the pivot ring to the stay ring.
In the prior art design as shown in figs.l and 2, the pivot ring is directly bolted to the stay ring (2). During concreting the pivot ring seating face of the stay ring generally goes out of level to the tune of 1.5 mm due to unequal shrinkage of the concrete and other associated factors. This seating face of the stay ring which goes out of level after concreting is corrected by manual overhead grinding. This correction process is very tedious and time consuming. On account of the corrective grinding, the guide vane passage height might reduce if positive

allowance is not provided on pivot ring flange face at the design stage in anticipation of this distortion.
Apart from problems of initial erection, there are problems of settlement of the powerhouse concrete at certain earth-zones, due to which the pivot ring seating face of the stay ring goes out of level. The seating faces again need to be ground to a horizontal level and the whole guide apparatus is to be assembled again with lots of rectification work.
In fig.3 of the prior art, the lower stationery labyrinth (3) is centralized with respect to the runner (4) using radial jacking screws with flat ends. After centralizing the labyrinth, it is doweled with the pivot ring to lock its position and to restrain its movement in the direction of rotation of the runner (4). This dowelling (5) is an overhead drilling and reaming operation which is very difficult being in a location with poor accessibility. Quite often the labyrinth geometry and diameters have to be changed for dowelling accessibility.
Sometimes, the labyrinth (3) has to be recentralized due to non-uniform wear of the rotating and stationery labyrinths.
Thus, after centralizing operation or replacement of the labyrinth by a spare one, dowelling has to be carried out, all of which mean additional work vis-a-vis generation loss.
Repeated redowelling of the labyrinth is also a major problem.
As shown in fig. 10 in the prior art design in which the pivot ring is bolted/suspended from the stay ring (2), the draft tube cone (6) is in-turn bolted to the pivot ring/suspended from the pivot ring. The dismantling joint (7) is at

the bottom end of the draft tube cone (6) where it joins with the draft tube elbow (bend liner).
This design has the following two drawbacks:
i) The downward hydraulic load on the pivot ring deflects the pivot ring (1) downward and wipes out the bearing clearances of the guide vane pivot stem and its bush. Thus, unless the rigidity of the pivot ring (1) is enhanced the guide vanes (8) may seize in the pivot ring (1). ii) The flow induced vibrations of the draft tube cone (6) get transferred to the pivot ring (1) to a significant extent on account of the large overhang from bolting point of the pivot ring-stay ring (1,2) to bottom free end of the draft tube cone (6).
As shown in fig. 11, the prior art design in which the pivot ring (1) is bolted to the stay ring (2) i.e. pivot ring (1) is suspended from the stay ring (2). The draft tube cone (6) is anchored at its bottom end i.e. the draft tube cone (6) is bolted to the flange on draft tube elbow. The dismantling gap (9) is at the top end i.e. at the joint of the draft tube cone (6) to the pivot ring (1).
As compared to the first prior art, the second prior art has the advantage that the flow induced vibrations of the draft tube cone (6) do not get significantly transferred to the pivot ring (1) as the draft tube cone (6) gets reasonably isolated from the pivot ring (1), on account of the dismantling gap (9) being at the top of draft tube cone (6).
However, this design still suffers from the drawback of the downward deflection of the pivot ring (1), for arresting the rigidity and hence the weight of the pivot ring (1) has to be greatly enhanced.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an adjustable pivot ring whereby the guide vane passage height can be adjusted to set the desired guide vane top and bottom clearances.
Another object of the invention is to propose an adjustable pivot ring which enables adjustment of guide vane passage height and further eliminates the process of dowelling of the lower stationery labyrinth with pivot ring after centralizing of the labyrinth with runner.
A further object of the invention is to propose an adjustable pivot ring with a support arrangement which enables adjustment of guide vane passage height, eliminates the process of dowelling of the lower stationery labyrinth and further reduces downward deflection of the pivot ring thereby preventing seizure of the guide vane pivot stems in their bushes.
A still further object of the invention is to propose an adjustable pivot ring with a support arrangement which enables adjustment of guide vane passage height, eliminates the process of dowelling of the lower stationery labyrinth, reduces downward deflection of the pivot ring and thereby reduces cost of the pivot ring.
SUMMARY OF THE INVENTION
According to the present invention the Pivot ring (1) of a Francis turbine with bottom dismantling is provided with an adjustment device for adjusting guide vane passage height and in-turn the guide vane top and bottom clearances. By use of this adjustment device, guide vane top and bottom clearances can be restored after some wear of the liner plates, thus prolonging the life of liner

plates before final replacement. This leads to reduction in duration of shutdowns and hence minimization of generation loss.
The present invention for centralizing the lower stationery labyrinth provides spherical ended screws which engage in conical depressions, thus dispensing the requirement of overhead dowelling in inaccessible locations and also the necessasity of redowelling after replacement of labyrinth.
In the present invention, the pivot ring for a Francis type hydro turbine having facility for bottom removal of runner is provided with a support device on the top of the draft tube cone. The support device below the suspended pivot ring reduces the deflection of the pivot ring.
This prop/support provided at the bottom end of the pivot ring substantially reduces the inertia/strength requirement of the pivot ring as well as the bolts holding pivot ring to the stay ring. Reduced inertia requirement in turn substantially reduces the material content and therefore, the cost of the pivot ring.
Also provision of the support device below the pivot ring significantly reduces the vibration level of the pivot ring.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig-l Sectional elevation of a guide apparatus of prior art (Without any feature for adjusting guide vane passage height).
Fig-2 Detailed view of part of section thru of a conventional type bottom dismantling type of Francis turbine of Prior art.

Fig-3 Prior art arrangement of labyrinth centralizing feature for a bottom dismantling type of Francis turbine.
Fig-4 Sectional elevation (with arrangement for adjusting guide vane passage height centralizing labyrinth and prop/support on pivot ring) as per the present invention
Fig-5 Detailed view of part of section thru of a bottom dismantling type of Francis turbine with adjustable top and bottom clearances as per the present invention
Fig-6 Enlarged view of top and bottom clearances adjustment feature for a bottom dismantling type of Francis turbine as per the present invention
Fig-7 Exploded view of top and bottom clearance adjustment feature for a bottom dismantling type of Francis turbine as per the present invention
Fig-8 New arrangement of labyrinth centralizing feature for a bottom dismantling type of Francis turbine as per the present invention
Fig-9 New arrangement of labyrinth centralizing feature for a bottom Dismantling type of Francis turbine as per the present invention
Fig-10 Prior Art 1- Pivot ring suspended from stay ring with dismantling gap at the bottom end of draft tube cone
Fig-11 Prior Art 2- Pivot ring suspended from stay ring and draft tube cone anchored at the bottom end with dismantling gap at the top end of draft tube cone

Fig-12 Pivot ring with prop/support on draft tube cone (Dismantling gap at the top end of draft tube cone)
Fig-13 Overall view of prop/support arrangement for pivot ring on upper draft tube cone as per the present invention
Fig-14 Close-up view of prop/support for pivot ring as per the present invention
Fig-15 Exploded view showing details of pivot ring prop/support design as per the present invention
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
As shown in figs 4,5,6&7, the pivot ring (1) flange face is not in direct contact with the corresponding seating face of the stay ring (2) but through leveling adaptors and pads.
Around each of the plurality of studs (26) holding the pivot ring (1) with the stay ring (2) a concentric threaded leveling adaptor (22) and a pad (23) is provided towards the outer diameter of the pivot ring flange. The threaded leveling adaptor (22) has two rows of six holes each i.e. 12 holes for turning the adaptor (22) by a tommy bar in a constricted space. As shown in fig.4, the stay ring (2) is connected to the spiral casing (33).
The nominal projection of the adaptor (22) above the pivot ring flange face is about 3 to 4 mm. The guide vane passage height at various uniform locations is measured with a stick micrometer and recorded. The passage height Would generally found be less than the required. Now, in steps as shown in fig.6, the

nuts (27) holding the pivot ring (1) are loosened. To ensure that the studs (26) do not loosen during loosening of the nuts (27), the studs (26) are held in a position by an extension bar with rectangular end (24) engaging into a rectangular slot (25) at the end of the studs (26). The studs (26) are thus held tight while the nuts (27) are being loosened. When the nuts (27) are loosened the pivot ring (1) slides down by self weight. Progressively this adjustment is done till the desired guide vane passage height is achieved to get the required guide vane top and bottom clearances. Once this is achieved the threaded leveling adaptor (22) is turned by tommy bar (34) till the adaptor top face touches the stay ring flange face. After this operation, the pivot ring (1) is lowered down and the pads (23) by the side of adaptor (22) are assembled. The top of each pad (23) is brought in level with top of the leveling adaptor (22). This adjustment is done either by grindling the top of the pads (23) or putting stainless steel shims below the pads (23) depending on each case. The pivot ring (1) is assembled back with the pads (23) ground flush with the corresponding pads (23). The adaptor can then be locked by putting a tommy bar (34) in it and welding a sleeve (35) to the stay ring (2) as shown in fig.6.
In the prior art, rubber seal to prevent water leakage was disposed between the flange faces of the pivot ring (1) and the stay ring (2). According to the invention, the rubber seal (28) is shifted to the sliding diametric fit between the stay ring (2) and the pivot ring (1), because there is gap between the flange faces of the stay ring (2) and the pivot ring (1).
This feature is very convenient and saves lot of erection time as overhead grinding work is totally eliminated.
After some years of operation of the turbines when the liners plate have worn out, the worn out surfaces can be ground smooth to a level and the increased guide vane (8) passage can be restored by use of the leveling adaptor (22).

Without this feature the liner plates would have to be replaced which calls for a major shut down leading to generation loss.
As shown in figs 8&9, a plurality of spherical/ball ended screws (11) are provided which engage into conical depressions (12). The spherical ended screws (11) with spherical end (30) when tightened against the conical depressions (12) provide the necessary radial support as well as constraint in the direction of rotation of the runner. Thus, with about forty spherical ball ended screws (11) touching the conical depressions (12) serve the functions of dowel, thereby eliminating the dowelling step required according to prior art after each centralizing. The spherical ball ended screws (11) are provided with either hexagon or square socket (31) at the other end for tightening the screws. The screws are locked by a dome type lock nut (29) with a sealing (32) tp prevent water leakage. After this, studs (36) for vertical clamping of lower labyrinth are tightened.
As shown in fig. 12,13,14 and 15, for the support device, the shape of the ribs (20) on the top draft tube cone (6) is modified to accommodate a pad (14). A nut portion (18) of the support screw (17) is disposed on the top of the pad (14). The support screw (17) bears against a hardened disc (15) which is fixed to the bottom of the pivot ring (1) by screws (16). After the support screw (17) is tightened against the pivot ring (1), it is locked by the locknut (18).Thus a significant portion of the hydraulic load on the overhang portion of pivot ring (1) gets transferred through the support screws (17) and draft tube ribs (20) to the concrete thus improving rigidity of the whole system. Also the vibration levels of the pivot ring (1) and the draft tube cone (6) reduces significantly.

WE CLAIM
1. An adjustable pivot ring for absorbing manufacturing and erection variations of Francis Turbines with bottom dismantling comprising:
- a pivot ring (1) having a flange face connected to the seating face of stay ring (2) through a plurality of leveling adaptors (22) and pads (23);
- a plurality of studs (26) and nuts (27) holding the pivot ring (1);
- at least one extension bar (24) with rectangular end (24) engaging into a rectangular slot (25) at the end of the studs (26) for holding the studs (26) in tight position when the nuts (27) are loosened;
- a plurality of spherical ball ended screws (11) engaged with a plurality of conical depressions (12) of the lower labyrinth (3) for providing radial support to the pivot ring (1) and for restraining its movement in the direction of rotation of the runner (4);
- a plurality of ribs (20) provided on the top draft cone (6) for accommodating a plurality of pads (14) carrying at least one nut (18) of a support screw (17) on top of each pad (14);
- a plurality of hardened discs (15) fixed to the pivot ring (1) by fixing a plurality of screws (16) and tightened against the pivot ring (1) by the support screw (17) and locked by the locknut (18) for transferring the hydraulic load on the overhang portion of the pivot ring (1) to the concrete which arrest the vibration of the pivot ring
(1) and the draft tube cone (6).

2. The adjustable pivot ring as claimed in claim 1, wherein the nuts (27) holding the pivot ring when loosened the pivot ring (1) is downwardly slidable by self weight for progressive adjustment of pivot ring (1).
3. The adjustable pivot ring as claimed in claim 1, wherein the threaded leveling adaptor (22) adjust its top face touching the stay ring (2) flange accommodates each pad (23) in level with its top between pivot ring (1) and the stay ring (2).
4. The adjustable pivot ring as claimed in claim 1, wherein one of rubber seals (28) is diametrically fixed in the radial gap between the bore of the stay ring (2) and outer diameter of the pivot ring (1) which prevents water leakage from the joint of pivot ring (1) and stay ring (2).
5. The adjustable pivot ring as claimed in claim 1, wherein the plurality of spherical ended screws (11) when tightened against a plurality of conical depression (12) of the lower labyrinth (3) serves the dual function of centralizing and dowelling.
6. A method for adjusting the guide vane passage height including centralizing the labyrinth in Francis type hydro turbines with bottom dismantling facility in order to absorb the variations that crop up during manufacturing and after concreting of stay ring at site, the method comprising;
Adjusting the guide vane passage height by a plurality of leveling adapters (22) and pads (23), the pivot ring (1) flange face being connected to the seating face of a stay ring (2), the pivot ring held by a plurality of studs (26) and nuts (27);

holding the studs (26) in tight position when the nuts (27) being loosened by at least one extension bar (24) with rectangular end engaging into a rectangular slot (25) at the end of the stud (26);
providing a radial support to the lower labyrinth (3) and restraining the movement of the lower labyrinth in the direction of rotation of runner (4) by means of a plurality of spherical ball ended screws (11) through engaging with a plurality of conical depressions (12) of the lower labyrinth (3); and
fixing a plurality of hardened discs (15) to the pivot ring (1) by a plurality of fixing screws (16) said disc (15) being tightened against the pivot ring (1) by a plurality of support screws (17) and locked by a locknut (19) which transfer the hydraulic load on the overhang portion of the pivot ring (1) to the concrete and arrest the vibration of the pivot ring (1) including the draft tube cone (6).

An adjustable pivot ring in francis type hydroturbines with bottom dismantling facility which enables adjustment of the guide vane passage height including centralizing the labyrinth in order to absorb the variations that crop up during manufacturing and after concreting of stay ring at site consists of a pivot ring (1) having a flange face connected to the seating face of a stay ring (2) through leveling adaptors (22) and pads (23). A plurality of studs (26) and nuts (27) in conjunction with at least one extension bar (24) enables adjustment of pivot ring to provide required guide vane passage height with top and bottom guide vane clearances. A plurality of spherical ball ended screws (11) being engaged with conical depression of lower labyrinth (3) provides support to the lower labyrinth in the radial and tangential direction thus dispensing the requirement of dowelling. A plurality of hardened disc being fixed to pivot ring (1) transfers the hydraulic load through support screws (17) nut portion (18) pads (14) on ribs (20) of draft tube cone (6) to concrete and arrests the vibrations of pivot ring (1) and draft tube cone (6).