
7.2 Repair of Seating Area
Any trim part which is scored or has damage on
guiding surfaces, to the extent that the same
could interfere with proper valve action, should
be replaced.
Minor scratches or nicks in seating surfaces of
either the plug or seat ring, should be repaired
in the following manner:
A. Lapping the Pilot Seat for 41400 Series
Valves (Auxiliary Pilot Plug Design)
After the pilot seat has been turned, it must be
ground as follows:
1. Apply a good grade of fine grinding
compound at several spots equally spaced
on the periphery of the seating surface of
the plug.
2. Place the pilot, with stem attached, in the
seated position without assembling the
pilot spring (22).
3. To facilitate lapping, screw a rod with T-
handle on top of the valve stem and secure
with a locknut. Or as an alternative, drill a
hole through a small flat
Figure 11
Models
Angle-A Angle-B
(Deg.) (Deg.)
piece of steel and fasten it to the plug stem with
two locknuts.
4. Lap by rotating the plug in short
oscillation strokes. After 8 or 10 strokes,
O
lift plug and turn 90 . Repeat the lapping
operation.
Note: Intermittent lifting is important
to keep the plug and seat concentric
during lapping. The lapping operation
should be repeated four times before
removing the pilot. If there is a dull
grey ring around the entire seat, the
lapping is complete. The grey area must
be as thin as possible. Do not lap to
cover the complete seat area width.
This will destroy the effectiveness of
the seat. If the ring is not continuous
repeat the entire lapping operation
until the ring is continuous. Remove all
the compound when the lapping
operation has been completed.
Reassemble the pilot in valve plug.
B. Lapping of Main Seat for 41100, 41200,
41300, 41400, 41500, 41600, 41700 &
41900 Series Valves.
If seating surfaces on the valve plug and seat
ring show signs of minor damage, they should
be turned on a lathe, to remove the damaged
areas. However, not more than 0.010" (0.25
mm) material should be removed in case 2", 3"
or 4" (50,80 or 100 mm) sizes. for sizes 6"
through 32" (150 through 800 mm), not more
than 0.015 (0.4 mm) material should be
removed. The seat angles shown in Figure 11
must be followed.
Lapping the main seat can be done in the same
manner as described above of pilot seat.
However the trim including the gaskets should
be assembled in the body. In case of sizes 6"
(150 mm) and above, the flat spring (19) should
also be assembled.
The bonnet, with the guide bush (23) in it
should be temporarily placed in position to act
as an alignment fixture for the lapping
operation. Four nuts spaced equally apart may
be tightened to keep the bonnet in position.
Caution: Do not tighten the nuts to the
required torque as the bonnet is being
used temporarily for guiding purpose.
7.3 Stroke Change
Stroke change is possible at site for an existing
41000 series valve equipped with MIL 37/38
spring diaphragm actuators.
This can be easily performed at site provided the
plug stem (1) is adaptable to the new stroke. If
the required stroke is less than existing valve
stroke, same can be
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