NIBCO Check Valve Automatic Stop F869B - Manual (Page 5)

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The full operation of this adjustment is only of a turn, 90°, from full open to full close.
5. Remove and discard the gasket between the bonnet and the top lid of the dashpot
cylinder. It is not worth the gamble to use an old gasket over again when you consider
the valve my leak at the joint afterwards.
6. Mark the dashpot cylinder and body with an ink marker or chalk for alignment when
reassembling. The dashpot cylinder may be stuck to the body. Carefully pry the lip of the
dashpot cylinder to loosen. Remove the dashpot cylinder. Remove the piston-disc
assembly. Lift straight up so as not to bend the disc pilot on the bottom of the disc.
7. Remove and discard the gasket between the body of the valve and underside of the lip
on the dashpot cylinder. Carefully clean gasket surfaces.
8. Inspect the valve carefully for evidence of wear, buildup of scale, other foreign matter
and any other problem which may cause the valve to operate erratically or incorrectly. It
will not be necessary to disassemble the piston-disc, disc seat and pilot to thoroughly
examine all components. It will be necessary to examine the piston rings for wear or
damage. If they are worn or damaged, they must be replaced. They are not repairable.
Be very careful not to score or mark any of the components while examining them. This
is an unhandy procedure so extra care must be taken. It is easy to break or bend the
disc pilot on the bottom of the disc if proper care is not taken. The piston rod cannot be
removed from the disc or the piston, as it is all one piece.
9. Clean all components as necessary, except the seating surface on the disc and in the
body seat. Use light emery cloth of fine sand paper so no large scratches are made on
the operating surfaces or sealing surfaces. Check the disc pilot hole in the bottom of the
body seat cage.
10. Replace any damaged and non-repairable components. It is always better to change a
questionable component then to use it.
11. If the disc and seat are leaking and need to be renewed, cut strips of 120 grit emery
paper about 1-1/2” long and 3/8” or 1/2” wide. Using double-backed adhesive tape, stick
strips on the seat ring seating surface. The strips should be evenly spaced around the
seat. Place the disc in the body and rotate the disc back and forth with very light
pressure. The further around you can rotate, the better the surface you will get. Finish up
with full rotation. Examine surface periodically, and the new surface will be seen
developing. When complete, the new surface on the disc should be all the way across
equal to the width of the seat ring seating surface.
12. Repeat this previous step on the seat ring by placing the strips of emery and double-
backed tape on the disc.
13. Clean thoroughly then rotate the disc once or twice lightly in the seat. A shiny line should
appear all the way around on the disc and the seat ring. Repeat the above steps until
this shiny line can be clearly seen. This line must be unbroken if a good seal is to be
achieved. A break in the line is a place the valve will leak. Repeat as needed.