Lapping Seats - Emerson Fisher EHD Instruction Manual

Instruction Manual
D100394X012
1. With the valve plug (key 3) removed according to the Trim Removal procedure, proceed as appropriate:
For the EHD valve, the piston rings (key 8) are each in two sections; remove the sections from the grooves in the valve
plug.
For the EHS valve, proceed to step 2.
For the EHT valve, work the retaining ring (key 10) off the valve plug with a screwdriver. Carefully slide the backup ring
and seal ring (keys 9 and 8) off the valve plug. For an NPS 6 valve with a level D Whisper Trim III cage, also remove the
piston ring (key 30) from the grooves in the valve plug.
2. To replace the valve plug stem (key 4), drive out the pin (key 5), and unscrew the stem from the valve plug.
CAUTION
Never reuse an old stem with a new valve plug or reinstall a valve stem after it has been removed. Using an old stem with a
new plug requires drilling a new pin hole in the stem. This weakens the stem and may cause the stem to fail in service. If a
new valve plug is required, always order a valve plug, stem, and pin as an assembly. Specify the correct part number of each
of the three parts, but state that the parts are being ordered as an assembly.
A used valve plug may be reused with a new stem. An exception is the Cavitrol III plug/stem assembly which must be
ordered and replaced as a unit.
3. Thread the new stem into the valve plug and tighten it to the appropriate torque value given in table 10. Using the
valve plug pin hole as a guide, drill the pin hole through the stem. Refer to table 10 for drill sizes.
4. Drive in the pin to lock the assembly.
5. If it is necessary to lap the seating surfaces, complete the Lapping Seats procedure before installing the EHD piston
rings or the EHT seal ring. The Trim Replacement procedure provides piston ring and seal ring installation
instructions and valve reassembly instructions.

Lapping Seats

Key numbers referenced in this procedure are shown in figure 18 for the EHD valve, in figure 19 for the EHS valve, and
in figure 20 for the EHT valve unless otherwise indicated.
Seating surfaces of the valve plug (key 3) and the seat ring (key 6) can be lapped for improved shutoff. Use a good
quality lapping compound with a mixture that contains 280 to 600 grit. Apply the compound to the bottom of the
valve plug. Use the following procedure to lap the seating surfaces.
1. Install the following parts according to the instructions presented in the Trim Replacement procedure: seat ring
gasket or O‐ring (key 12), seat ring (key 6), seat ring retainer (key 7), cage (key 2), cage gaskets (key 11), and if
used, the O‐ring (key 26, figure 21).
2. Proceed as appropriate:
For an EHD or EHT valve, install the valve plug and stem assembly (keys 3 and 4)—without piston rings or seal ring (keys
8 and 30)—into the cage.
For an EHS valve, install the valve plug and stem assembly (keys 3 and 4) into the cage.
3. Install the bonnet (key 1, figure 16) over the valve stem, and secure the bonnet with four of the hex nuts (key 14).
4. Attach a handle, such as a piece of strap iron secured by stem locknuts, to the valve stem. Rotate the handle
alternately in each direction to lap the seats.
Note
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. If possible, clean the parts without disturbing their positions. If the parts
must be removed for cleaning, return them to the original positions.
EH (1-1/2x1 through 8x6)
July 2017
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