Valve Plug Maintenance - Fisher EWS Series Instruction Manual

EW Valve
locked to the valve plug stem with nuts. Rotate the
handle alternately in each direction to lap the seats.
After lapping, remove the bonnet, and clean the seat
surfaces. Completely assemble the valve as
described in the Trim Replacement portion of the
Trim Maintenance section, and test the valve for
shutoff. Repeat the lapping procedure if leakage is
still excessive.

Valve Plug Maintenance

Except where indicated, key numbers in this section
are referenced in figure 22 for Design EWD valve
plugs, figure 11 for Design EWS valve plugs, and
figure 24 for Design EWT valve plugs.
CAUTION
If replacing the piston ring (key 6) or
seal ring (key 28), be careful not to
scratch the surfaces of the ring groove
in the valve plug or any of the surfaces
of the replacement ring, or the
replacement ring may not seal
properly.
1. With the valve plug (key 2) removed, according to
the Trim Removal section, proceed as appropriate:
For the Design EWD carbon-filled PTFE piston
ring, the ring is split in one place. If there is visible
damage, spread the ring slightly, and remove it from
the groove in the valve plug. To install a carbon-filled
PTFE piston ring, spread the ring apart slightly at the
split, and install it over the stem and into the groove
in the valve plug. The open side must face along the
stem, depending on flow direction, as shown in view
A of figure 22.
For each Design EWD graphite piston ring, the
ring can be easily removed since it is in two pieces.
A new graphite piston ring is furnished as a
complete ring. Use a vise with smooth or taped jaws
to break this replacement ring into halves. Place the
new ring in the vise so that the jaws will compress
the ring into an oval. Slowly compress the ring until it
snaps on both sides. If one side snaps first, do not
try to tear or cut the other side. Instead, keep
compressing the ring until the other side snaps. Be
sure to match the broken ends when installing the
ring in the valve plug groove.
For the Design EWT two-piece seal ring, the ring
cannot be reused as it is a closed ring, which must
be pried and/or cut from the groove. Then the
elastomeric backup ring (key 29) can be spread
slightly and removed.
14
To install a new two-piece seal ring, apply a general
purpose silicone-base lubricant to both the backup
ring and seal ring (keys 29 and 28). Place the
backup ring over the stem (key 7) and into the
groove. Place the seal ring over the top edge of the
valve plug (key 2) so that it enters the groove on one
side of the valve plug. Slowly and gently stretch the
seal ring, and work it over the top edge of the valve
plug. The PTFE material in the seal ring must be
permitted time to cold-flow during the stretching
procedure; so avoid jerking sharply on this ring.
Stretching the seal ring over the valve plug may
make it seem unduly loose when in the groove, but it
will contract to its original size after insertion into the
cage.
For the Design EWT spring-loaded seal ring, the
ring used on a valve plug having a 136.5 mm (5.375
inch) or less port diameter may be removed
undamaged by first working the retaining ring
(key 27) off with a screwdriver. Then carefully slide
the metal backup ring (key 29) and seal ring (key 28)
off the valve plug (key 2). The spring-loaded seal
ring used on a valve plug having a 178 mm (7-inch)
or greater port diameter must be carefully pried
and/or cut from its groove. Therefore, it cannot be
reused.
A spring-loaded seal ring must be installed so that its
open side faces toward either the top or the bottom
of the valve plug, depending on flow direction, as
shown in view A of figure 22 or 24. To install a
spring-loaded seal ring on a valve plug with a 136.5
mm (5.375 inch) or less port diameter, slide the seal
ring (key 28) onto the valve plug followed by the
metal backup ring (key 29). Then install the retaining
ring (key 27) by inserting one end in the groove and,
while turning the plug, press the ring into the groove.
Again, be careful not to scratch any surfaces of the
ring or plug.
To install the seal ring on a valve plug with 178 mm
(7-inch) or greater port diameter, lubricate it with a
general purpose silicone-base lubricant. Then gently
stretch the seal ring, and work it over the top edge of
the valve plug. The PTFE material in the seal ring
must be permitted time to cold-flow during the
stretching procedure; so avoid jerking sharply on the
ring. Stretching the seal ring over the valve plug may
make it seem unduly loose when in the groove, but it
will contract to its original size after insertion into the
cage.
CAUTION
Never reuse an old stem or adaptor
with a new valve plug. Using an old
Instruction Manual
Form 2376
March 2007