Fisher HPA Instruction Manual page 12

HP and HPA Valves
July 2017
Note
The following step also provides additional assurance that the valve body fluid pressure has been relieved.
5. Hex nuts (key 14) attach the bonnet to the valve body. Loosen these nuts or cap screws approximately 3 mm (1/8
inch). Then loosen the body‐to‐bonnet gasketed joint by either rocking the bonnet or prying between the bonnet
and valve body. Work the prying tool around the bonnet until the bonnet loosens. If no fluid leaks from the joint,
proceed to the next step.
6. Unscrew the hex nuts (key 14) and carefully lift the bonnet off the valve stem. If the valve plug and stem assembly
starts to lift with the bonnet, use a brass or lead hammer on the end of the stem and tap it back down. Set the
bonnet on a cardboard or wooden surface to prevent damage to the bonnet gasket surface.
7. Remove the valve plug (key 5), bonnet gasket (key 11), cage (key 2), seat ring (key 4), and the seat ring gasket (key
12).
CAUTION
Inspect the seat ring, cage, bonnet, and body gasket surfaces. These surfaces must be in good condition, with all foreign
material removed. Small burrs less than approximately 0.076 mm (0.003 inches) in height (the thickness of a human hair)
can be ignored. Scratches or burrs that run across the serrations are not permitted under any conditions, since they will
prevent the gaskets from sealing properly.
8. Clean all gasket surfaces with a good wire brush. Clean in the same direction as the surface serrations, not across
them.
9. Cover the opening in the valve body to protect the gasket surface and to prevent foreign material from getting into
the valve body cavity.
10. Remove the packing flange nuts (key 21), packing flange (key 19), upper wiper (key 27), and packing follower (key
28). Carefully push out all the remaining packing parts from the valve side of the bonnet using a rounded rod or
other tool that will not scratch the packing box wall. For extension bonnets, also remove the baffle (key 36 ) and
retaining ring (key 37).
11. Clean the packing box and the following metal packing parts: packing follower, packing box ring (key 26), spring
or lantern ring (key 24), and, for single arrangements of PTFE V‐ring packing only, special washer (key 25).
12. Inspect the valve stem threads for any sharp edges that might cut the packing. A whetstone or emery cloth may
be used to smooth the threads if necessary.
13. Remove the protective covering from the valve body cavity, and install the seat ring and cage using a new seat ring
gasket (key 12) and bonnet gasket (key 11). Install the plug, then slide the bonnet over the stem and onto the studs
(key 13). For a valve body with extension bonnet, also install the baffle and retaining rings (keys 36 and 37).
Note
The prelubricated hex nuts (key 14) referred to in step 14 can be identified by a black film coating on the nut threads.
The proper bolting procedures in step 14 include‐‐but are not limited to‐‐ensuring that the bonnet stud threads are clean, and that
the hex nuts are evenly tightened to the specified torque values.
12
Instruction Manual
D101634X012