Fisher HPA Instruction Manual page 18

HP and HPA Valves
July 2017
Note
HP Series valves use spiral‐wound gaskets. These gaskets provide their seal by being crushed and therefore should never be
reused. This includes reusing a gasket after the lapping procedure has been performed.
And "old" gasket can be used to lap the seat, however the gasket must be replaced with a new gasket.
To preserve the effects of lapping, do not change either the position of the seat ring in the valve body cavity or the position of the
cage on the seat ring after lapping the seating surfaces. When the parts are removed for cleaning and replacement of the "old"
gaskets, return them to the original positions.
Figure 8. Typical Balanced TSO Trim (1.6875 Inch Port Diameter)
A7112
Use the following procedure to lap the seating surfaces.
1. Install the following parts according to the instructions presented in the trim replacement procedure: "old" seat
ring gasket (key 12), seat ring (key 4), cage (key 2), and "old" bonnet gasket(key 11).
2. Proceed as appropriate:
For an HPD, HPAD, HPT, or HPAT valve, install the valve plug and stem assembly (keys 5 and 6)‐‐without piston rings or
seal ring (key 8) ‐‐into the cage.
For an HPS or HPAS valve, install the valve plug and stem assembly (keys 5 and 6) into the cage.
3. Install the bonnet (key 18) over the valve stem, and secure the bonnet with four of the hex nuts (key 14).
18
VALVE
PLUG
SEAL
PROTECTED
SOFT SEAT
Instruction Manual
D101634X012