WICKET GATE ADJUSTMENT
When reassembling a unit following an overhaul, it is very important that the heel to toe clearance between
wicket gates be uniform and tight to ensure a good seal when the unit is watered up and to evenly distribute
the force from the servomotors. Turnbuckles or eccentrics in the wicket gate linkage are provided to adjust
the individual gates.
A ratcheting hoist or "come-a-long" and sling are frequently used to make the initial adjustment to the
gates. Extreme caution must be used when using this procedure to prevent overloading the sling or
the hoist. The sling used must
have a rating higher than the hoist, and the hoist must have some type
of overload indication. With the gates and the headcover installed but prior to attaching the linkage
between the gate arms and the shift ling, a sling is looped around the outside of the wicket gates and
attached to the hoist. As the hoist is tightened, the sling draws the wicket gates closed. With the sling still
tight, the turnbuckles or eccentrics are adjusted so that the gate linkage can be connected.
Sometimes no further adjustment is required, but in many instances, there will be gaps between the gates
after the sling is released. If there are gaps, the first thing to determine is whether the gap is even from the
top to the bottom of the gate. If the gates are actually touching at the top with a gap at the bottom or vice
versa, the gate seal areas are not parallel to the gate shafts or the gates are not parallel to one another. In
either case, there is little that can be done with the unit assembled. A determination must be made as to
whether the gaps are acceptable. The amount of gap that is acceptable will depend on the unit and the
number of gates with gaps. A high head unit will require tighter tolerances than a low head unit. The
"squeeze" provided by the servomotors can take up some of the gap, but this will unevenly distribute the
pressure to the gates and can, in severe cases, cause failure of the shear pins.
If there are gaps that are even top to bottom, the first step in eliminating these gaps is to consolidate all the
gaps to one gap. The first step in accomplishing this is to disconnect all of the wicket gate linkage so that
each gate, is free to move independently. One gate is then chosen to be a "master" gate, and it is opened
slightly (i.e. less than 0.020 inch). Next the heel or the toe of the next gate, depending on the geometry of
the wicket gate, is adjusted to just contact the master gate. Each of the following gates are adjusted in
order until there is one gap between the last gate and the master gate or between the last gate and the next
to last gate. This gap is removed by closing the master gate or the last gate, depending on where the gap is,
and then adjusting the rest of the gates in sequence until there are no gaps.
Dial indicators set up on the gate arms can facilitate the adjustment process. When adjusting the gates, the
dial indicators can be used to determine when the gates touch without having someone in the spiral case.
The dial indicator will indicate movement of the "stationary" gate when the gate being adjusted just makes
Two procedures for wicket gate adjustment are listed below. The procedure used will depend on the
geometry of the wicket gates. The distance from the contact points or seal areas of the gates to the center
of the gate shaft should be checked on the turbine