d. If wicket gate bushings are worn beyond manufacturer's tolerances they are
generally replaced with bushings made from bearing bronze UNS C93200.
New wicket gate bushings must be line bored or the concentricity of the bushing
fit holes established and close tolerance bushings procured. Unless otherwise
specified by the manufacturer the bushings should be plumb and concentric
within 0.00005 multiplied by the vertical distance between the top and bottom
Self lubricated bushings are now available that eliminate the need for periodic
greasing. These bushings should be considered in locations where water quality
standards prohibit contamination by even small quantities of grease. Reclamation has
not had sufficient experience with this type of bushing to determine its long term
a. Objectives - As discussed in section 4, paint and other nonfused coatings
such as epoxies and ceramic metals offer poor resistance to cavitation pitting
and should not be applied simply as a cavitation barrier.
Paint and other thin coatings on the wicket gates and runner do not significantly
impact efficiency or unit performance unless they are of sufficient thickness to
alter the form or contour of the surface.
In most cases painting or coating of the wicket gates and runner is effective only
in preventing corrosion and increasing visibility in the turbine.
b. Stainless steel - Stainless steel runners and wicket gates are generally left
unpainted to take advantage of the corrosion resistance of the material.
However, stainless steel is susceptible to rapid corrosion if it has been
contaminated with carbon from grinding or weld spatter.
The corrosion resistance of the stainless steel can sometimes be restored by
passivating the surfaces with a solution of I part (by volume) of 56 percent nitric
acid mixed with 9 parts (by volume) of water. After passivating, the surfaces
must be thoroughly rinsed with warm water and then swabbed with a 2 percent
(by volume) ammonia solution followed by an additional water rinse to remove
all traces of acid.