Trim Replacement - Fisher HPA Instruction Manual

HP and HPA Valves
July 2017

Trim Replacement

WARNING
Observe the warning at the start of the Maintenance section.
After all trim maintenance has been completed, reassemble the valve body by following the numbered steps below. Be
certain that all gasketed surfaces have been well cleaned. Key numbers referenced in this procedure are shown in
figure 17, 18, or 19, except where indicated.
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.
CAUTION
The pressure balancing holes in the valve plug are necessary for the proper and safe operation of the valve. Inspect the
balancing holes every time the valve is disassembled for service. Any build-up, blockage, or clogging of the balance holes
should be removed.
1. Install the seat ring gasket (key 12) into the valve body. Install the seat ring (key 4).
2. Install the cage.
Note
When installing the standard cage, align two of the holes in the cage with the centerline of the valve body. Refer to figure 18.
Constructions other than TSO trim
1. To install the piston rings and seal rings (key 8), proceed as appropriate:
For an HPD or HPAD valve, if it is necessary to install new piston rings, the replacement piston rings will arrive in one
piece. Use a vise with smooth or taped jaws to break a replacement piston ring into halves. Place the new ring in the
vise so that the jaws compress the ring into an oval. Compress the ring slowly until the ring snaps on both sides. If one
side snaps first, do not try to tear or cut the other side. Instead, keep compressing until the other side snaps. The
piston ring can also be fractured by scoring and snapping over a hard surface such as a table edge. Sawing or cutting is
not recommended.
Remove any protective tape or covering from the valve plug and stem assembly, and set it on a protective surface.
Then, place the piston rings in the piston ring grooves with the fractured ends matched.
For an HPT or HPAT valve, install the seal ring (key 8) onto the valve plug (key 5). Install the ring with the open side
facing the seat ring end of the valve plug for flow‐down applications (view A of figure 20) or with the open side facing
20
Instruction Manual
D101634X012