Lapping Seats; Trim Replacement - Fisher EHD Instruction Manual

Instruction Manual
April 2009
the valve plug pin hole as a guide, drill the pin hole
through the stem. Use a 1/4 inch drill for 31.8 mm
(1-1/4 inch) stems and a 3/8 inch drill for 50.8 mm
(2-inch) stems.
4. Drive in the pin to lock the assembly.
5. If seat lapping is necessary, complete the
Lapping Seats procedure before installing the EHD
piston rings or the EHT seal ring. Piston ring and
seal ring installation instructions and valve
body-to-bonnet reassembly instructions are
presented in the Trim Replacement procedure.

Lapping Seats

Key numbers referenced in this procedure are
shown in figure 12 for the EHD valve and in figure 13
for the EHT valve.
A certain amount of leakage should be expected
with metal-to-metal seating in any valve. If the
leakage becomes excessive, however, the condition
of the seating surfaces of the valve plug (key 3) and
seat ring (key 6) can be improved by lapping. (Deep
nicks should be machined out rather than ground
out.) 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. For all designs, install the seat ring gasket or
O-ring (key 12), seat ring (key 6), seat ring cap
screws (key 7), lower cage gasket (key 12), cage
(key 2), and upper cage gasket (key 12) into the
valve body per the instructions in the Trim
Replacement procedure.
2. Install the assembled valve plug and stem
(keys 3 and 4)--without piston rings or seal ring
(key 8)-- into the cage.
3. For all seating surfaces, install the bonnet (key 1,
figure 11) 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 plug stem.
Rotate the handle alternately in each direction to lap
the seats.
In order 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
Note
EH Valves (NPS 8 through 14)
parts without disturbing their
positions. If the parts must be
removed for cleaning, return them to
the original positions.
5. After lapping, again disassemble as necessary,
clean the seating surfaces, reassemble, and test for
shutoff. Repeat the lapping procedure if necessary.

Trim Replacement

After all trim maintenance has been completed,
reassemble the valve by following the numbered
steps below. Be certain that all gasketed surfaces
are clean. Key numbers referenced in this procedure
are shown in figure 12 for the EHD valve and in
figure 13 for the EHT valve.
Thoroughly clean the seat ring (key 6),
the seat ring cap screws (key 7), and
the cap screw threads in the valve
body with a good-quality degreaser.
Unless the valve is to be used for
oxygen service, thoroughly lubricate
the cap screw threads and the
underside of the cap screw heads with
one of the lubricants (or equivalent)
shown in table 7.
Failure to lubricate as described may
cause galling and improper seat ring
gasket or O-ring (key 12) loading
which may result in leakage.
If the control valve is to be used for
oxygen service, use the lubrication
procedure above, but substitute a
lubricant that has been approved for
oxygen service. Use of unapproved
lubricants creates a fire or explosion
hazard.
1. Install either the seat ring gasket or the O-ring
(key 12). Place the O-ring in the O-ring groove in the
seat ring before installing the seat ring in the valve
body. Install the seat ring (key 6) and secure it with
the seat ring cap screws (key 7). Torque the hex
socket head cap screws in a criss-cross pattern with
no more than 20 NSm (15 lbfSft) of torque. When all
are tightened to 20 NSm (15 lbfSft), increase the
torque 20 NSm (15 lbfSft) without exceeding the
torque value specified in table 7, and repeat the
CAUTION
WARNING
11