Trim Replacement - Fisher NPS 12 Instruction Manual

Large ET and ED Valves
July 2014
For ET valves with HTS1 option, install the seat ring seal ring (key 6) so that its open side faces the valve stem for
Cavitrol III trim and flow-down standard cages. Reverse the seal ring for Whisper Trim III, WhisperFlo, and flow-up
standard cages so its open side faces away from the valve stem. Lubricate the seal ring (key 6), backup ring (key 226),
anti-extrusion ring (key 225), and retaining ring (key 227) with a general-purpose, lithium-base lubricant, and slide the
seal ring, backup ring, and anti-extrusion ring over the seat ring according to figure 5, 6, or 7. Start the retaining ring in
the groove on one side of the seat ring, and gently work it over the seat ring.
4. For ED constructions, each of the piston rings (key 28, figure 5, 6, or 7) is in two pieces; remove the pieces.
Each new graphite piston ring is furnished as a complete ring, and each must be broken into two approximately equal
portions. Do this by placing the ring on edge on a smooth, hard surface and striking the ring squarely with a hammer.
Be sure to match the broken ends when installing the ring sections in the valve plug grooves.
CAUTION
Never reuse an old stem (key 7) with a new valve plug. Using an old stem with a new plug requires drilling a new pin hole in
the stem. This weakens the stem and may cause it to fail in service. However, a used valve plug may be reused with a new
stem.
5. To replace the valve stem (key 7), drill out the pin (key 8) and unscrew the stem from the valve plug.
6. Screw the new stem tightly into the valve plug. Drill through the stem, using a 1/4-inch diameter drill for the 31.8
mm (1-1/4 inch) stem diameter used in this valve. Use the hole in the valve plug as a guide. Remove any chips or
burrs, and drive in a new pin to lock the assembly.

Trim Replacement

Except where indicated, key numbers are shown in figure 5 and 6.
1. Proceed as appropriate:
For ET valves:
Insert cap screws in the two 3/8-inch tapped holes in the bottom of the seat ring (key 9). Use a bar to pry against the
cap screws and turn the seat ring (key 9) into the cage (key 3).
For all sizes, tack weld the seat ring to the cage using minimal heat. Two welds, 6 mm (1/4-inch) long and 180 degrees
apart, are required. Install the seat ring seal ring (key 6) so that its open side faces the valve stem for Cavitrol III trim
and flow-down standard cages. Reverse the seal ring for Whisper Trim III, WhisperFlo, and flow-up standard cages.
Lubricate the seal ring with a general-purpose, lithium-base lubricant, and place it over the bottom end of the seat
ring. Start the ring in the groove on one side of the seat ring, and gently work it over the seat ring.
For ET valves with HST1 option:
For all sizes, tack weld the seat ring to the cage using minimal heat. Two welds, 6 mm (1/4-inch) long and 180 degrees
apart, are required. For ET valves with HTS1 option, install the seat ring seal ring (key 6) so that its open side faces the
valve stem for Cavitrol III trim and flow-down standard cages. Reverse the seal ring for Whisper Trim III, WhisperFlo,
and flow-up standard cages so its open side faces away from the valve stem. Lubricate the seal ring (key 6), backup ring
(key 226), anti-extrusion ring (key 225), and retaining ring (key 227) with a general-purpose, lithium-base lubricant,
and slide the seal ring, backup ring, and anti-extrusion ring over the seat ring according to figure 5, 6, or 7. Start the
retaining ring in the groove on one side of the seat ring, and gently work it over the seat ring.
For ED valves (figure 6), install the seat ring gasket (key 13).
Temporarily install screws or bolts into the tapped holes in the seat ring (key 9), making sure the seating surface is
facing up. Lower the seat ring into the valve body. Remove the temporary screws or bolts.
14
Instruction Manual
D103553X012