Lapping Metal Seats - Fisher EWS Series Instruction Manual

Instruction Manual
Form 2376
March 2007
Whisper Trim III cage, remove the bonnet spacer
(key 32) and bonnet gasket (key 10) on top of the
spacer. Then on any construction with a cage
retainer (key 31), remove the cage retainer and its
associated gaskets. A Whisper Trim III cage retainer
has two 3/8-16 UNC threads in which screws or
bolts can be installed for lifting.
6. Remove the cage or cage/baffle assembly (key 3)
and the associated gaskets (keys 10, 11, and 12).
With full-capacity constructions that have FGM
gasket sets, a shim (key 53) is used instead of the
cage gasket (key 11). If the cage is stuck in the
valve, use a rubber mallet to strike the exposed
portion of the cage at several points around its
circumference.
7. For constructions other than TSO (tight
shutoff trim), remove the seat ring (key 9) or disk
seat (key 22), seat ring gasket (key 13), and the seat
ring adaptor (key 5) and adaptor gasket (key 14)
where used in a restricted-capacity construction.
Design EWS and EWT PTFE-seat constructions use
a disk (key 23) sandwiched between the disk seat
and disk retainer (key 21). A CL900 NPS 8x6 Design
EWT construction with Cavitrol III cage has its spiral
wound gasket (key 12) on the side of the seat ring
opposite the seat ring gasket.
8. For TSO (tight shutoff trim) constructions,
perform the following steps (refer to figures 7 and 8):
D Remove the piston ring, anti-extrusion rings,
backup ring, and retainer.
D Remove the set screws that lock the outer plug
to the inner plug.
D Using a strap wrench or similar tool, unscrew
the outer plug from the inner plug. Do not damage
the outer plug guide surfaces.
D Remove the protected soft seat seal.
D Inspect the parts for damage and replace if
needed.
9. For all constructions, inspect parts for wear or
damage that would prevent proper operation of the
valve. Replace or repair trim parts according to the
following procedures for lapping metal seats or other
valve plug maintenance procedures, as appropriate.
A7096 / IL
Figure 8. Typical Balanced TSO Trim

Lapping Metal Seats

CAUTION
To avoid damaging the ENVIRO-SEAL
bellows seal bonnet assembly, do not
attempt to lap the metal seating
surfaces. The design of the assembly
prevents rotation of the stem and any
forced rotation will damage internal
components of the ENVIRO-SEAL
bellows seal bonnet.
Except with respect to the ENVIRO-SEAL Bellows
Seal Bonnet assembly, with metal seat
constructions, seating surfaces of the valve plug and
seat ring (keys 2 and 9, figures 24 through 26) can
be lapped for improved shutoff. (Deep nicks should
be machined out rather than ground out.) Use a
good quality lapping compound of a mixture of 280
to 600-grit. Apply the compound to the bottom of the
valve plug.
Assemble the valve to the extent that the cage (and
cage retainer and bonnet spacer, if used) is in place
and the bonnet is bolted to the valve. A simple
handle can be made from a piece of strap iron
EW Valve
VALVE PLUG
SEAL
PROTECTED
SOFT SEAT
13