Wicket gate bearing seal

Hydraulic turbo machines including pumps and pump turbines having pivotally adjustable wicket gates are vulnerable to damage caused by the ingress of dirty water containing abrasive particles into the bushings in which the stems of the wicket gates are pivotally supported in the headcover and bottom ring. This problem is overcome by the provision of individual seals between the end of each wicket gate and an adjoining surface portion of the headcover or bottom ring in which the bushings are located. In addition, seal water at a pressure in excess of machine operating pressure forces the seal ring into contact with the end of the wicket gate and also causes a slight flow of clean water outwardly between the seal and the respective end of the wicket gate, so as to keep the seal entry zone flushed clear of particulate material.

BACKGROUND OF THE INVENTION 
This invention is directed to the construction of a hydraulic turbo-machine 
such as a pump or pump turbine, and in particular to a wicket gate stem 
seal to preclude ingress of contaminated water into the bearings of the 
wicket gates. 
In the case of turbo-machines such as Francis turbines or pump turbines 
having adjustable wicket gates the problem arises under conditions of 
operation with contaminated water containing abrasive particles that the 
bushings of the wicket gates may become infiltrated by the contaminated 
water, particularly under conditions of shut-down when the wicket gates 
are in the fully closed condition, or under base load conditions, when the 
setting of the wicket gates can remain unchanged for a matter of weeks at 
a time. The presence of such contaminants can result in a tendency of the 
wicket gate spindles to seize in their bushings under such conditions of 
operation, or to generate wear in the spindles and bushings and so cause 
inaccuracy in gate settings which can lead to overload of the control 
mechanism. Ultimately these effects of contamination can lead to machine 
failure, or at least necessitate taking the machine out of service, for 
purposes of maintenance. In as much as the wicket gates are normally 
relied upon to regulate machine operation, including the shutting down of 
the machine, the malfunctioning of the wicket gates can lead to very 
serious consequences. 
In the case of gas turbines, these machines are not considered to be 
analogous in their structure to water pumps and turbines, on account of 
the extreme differences in ambient temperature conditions, dynamic forces 
acting on the respective guide vanes, and totally different functional 
requirements between a hot and compressible gaseous working fluid and a 
cold, incompressible liquid working fluid. In gas turbine technology it is 
well known to introduce air as a lubricating fluid to the bearings of the 
variable guide vanes, as shown in U.S. Pat. No. 3,542,484, Mason, issued 
Nov. 24, 1970. Mason also shows a loading spring to axially load his guide 
vanes radially outwardly against the bearing seating, under shut-down 
conditions. The use of air as a cooling medium for the bearings of gas 
turbine guide vanes is shown in U.S. Pat. No. 3,582,231 Zerlauth, issued 
June 1, 1971. 
Sealing of the end surfaces of wicket gates is shown in U.S. Pat. No. 
3,947,147, Loktaeva et al, issued Mar. 30, 1976, in which an annular 
gasket is located between an axial end surface of the wicket gate and the 
rim of the housing. 
The prior art does not show the use of either gaseous or liquid fluid for 
purging purposes to avoid contamination of the vane bearings. 
Furthermore, the use of an axially spring loaded seal also is not known. In 
the case of U.S. Pat. No. 3,685,921, Dekeyser, issued Aug. 22, 1972, the 
blades of a gas turbine guide ring are biased radially inwardly against an 
inner casing. 
The problem of coping with contaminated water for driving a turbine, 
bearing abrasive solid particles is in no way approached in the prior art. 
In the extreme, abrasive particulate content as high as about 40% by 
weight has been known, on an irregular basis, and the present disclosure 
represents one effort to minimize some of the effects that such conditions 
may produce. 
SUMMARY OF THE INVENTION 
The present invention provides a wicket gate trunnion support system suited 
for use in pumps and pump turbines, having a plurality of wicket gates 
each pivotally mounted on a top stem extending from a recess in a 
head-cover of the machine and a bottom stem extending into a recess within 
a bottom ring of the machine, bearing means extending about each stem in 
interposed relation between the stem and the respective recess to provide 
transverse support to the gate, and stem seal means extending in 
substantial sealing relation with the recess and extending from the recess 
in coaxial relation with the stem, having an annular axial end face in 
sealing relation with an end surface of the gate, loading spring means 
exerting axial thrust to hold the stem seal means in loaded relation 
against the gate end surface and passage means connected to the recess to 
introduce liquid under pressure within the recess for passage outwardly 
towards the gate to preclude ingress to the seal means of working liquid 
passing through a main flow passage of the machine, to ensure gate 
operation capability at all times for opening the gates, and for closing 
the gates to shut down the machine. 
The stem seal means is maintained in sealed relation with the recess by 
means of an annular resilient seal ring. 
The stem bearing means may be sealed to the recess by way of an annular 
resilient seal ring such as an O-ring. Similarly an O-ring seal can be 
used to seal the stem bearing means to the stem to preclude extrusion of 
lubricant under the pressure of flushing liquid. 
The liquid supply means is generally pressurized to a value in excess of 
machine operating pressure, so as to maintain an outflow of the liquid in 
flushing relation past the stem seal means. 
The provision of a bearing bushing having a groove about the outer 
peripheral surface thereof to receive a sealing O-ring therein, and an 
annular gallery about the outer periphery of the bushing to receive 
sealing liquid from a passage in the headcover simplifies the arrangement.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, the Francis type machine has an annular scroll 10 
within which a runner 13 is supported by way of shaft 15. An annular array 
of wicket gates 12 are interposed between scroll 10 and runner 13 in flow 
controlling relation. 
The stems 22 of the wicket gates extend upwardly through the machine 
headcover 17 and downwardly into the bottom ring 19. 
Referring to FIG. 2, the arrangement 20 shows a wicket gate 12 having stem 
22 extending upwards through a cylindrical recess 27 in the headcover 17. 
A bearing bushing 21 is retained by keeper 23, being secured by capscrews 
24. The bushing 21 has an outer groove 31 within which an O-ring seal 32 
is located and a radially inner groove 33 within which an O-ring seal 35 
is located. 
An annular gallery 28 is located in axially aligned relation with a liquid 
supply passage 29. 
A stem seal 40 comprises an annular ring 42 having a lower axial end face 
44 in sealing relation with the adjoining end surface 19' of wicket gate 
12. A groove 41 contains an elastomeric O-ring seal 43 which seals against 
the headcover recess 27, to limit the consumption of flushing water. If 
the machining of ring 42 and recess 27 provides substantial sealing 
against such leakage, then the O-ring seal 43 may be dispensed with. 
A convoluted annular plate spring 45 interposed between bushing 21 and stem 
seal 40 serves to resiliently press the seal 40 in sealing relation 
against the end surface 19' of wicket gate 12, to serve as resilient axial 
loading means for the seal 40. 
A source of pressurized flushing liquid, (not shown), such as clean water, 
is connected supply passage 29. 
By controlling the pressure of the flushing liquid to a value slightly in 
excess of the pressure of the working liquid at the wicket gates, a 
minimal out-flow of flushing liquid is obtained, to preclude ingress of 
the working liquid into the stem bushing 21, while limiting the quantity 
of flushing liquid required. 
Where they are environmentally acceptable, alternative fluids may be 
considered, such as grease or oil.