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C. Remove bonnet (8), and plug stem (1) and plug (16) sub-
assembly together as one unit.
D. Since the cage (13), seat ring (14) and seat ring gasket (15) are
held in place by the bonnet, they may now be removed.
Note: Spiral wound gaskets (11 & 15) are standard in the
21000 Series design and it is imperative that new gaskets
WARNING
be installed each time the valve is disassembled.
E.
Remove packing flange stud nuts (3), packing flange (4) and
packing follower (5).
F.
Remove plug (16) and plug stem (1) sub-assembly from the
bonnet (8).
CAUTION
Care must be taken to avoid damage to the plug and
plug guide.
G. Remove old packing (6) [and optional lantern ring (7) if a
CAUTION
leak detection connection has been installed]. Refer to
Figure 5.
H. All components may now be inspected for wear and service
damage. After determining the maintenance required,
proceed to the appropriate Section of this instruction manual.
7. Maintenance & Repair
The purpose of this section is to provide recommended
maintenance and repair procedures. These procedures assume
the availability of standard shop tools and equipment.
7.1 Threaded Seat Ring Removal
(Figure 12 or 14)
Threaded seat rings (14) are installed tightly by the manufacturer,
WARNING
and after years of service they may be difficult to remove.
To facilitate removal, seat ring wrenches can be fabricated to
engage the seat ring lugs and adapted to a standard wrench. If
the seat ring is exceptionally resistant to removal, the application
of heat or penetrating oil should be helpful.
CAUTION
When using heating devices, ensure that proper
safety practices are observed. Flammability and
toxicity of the process fluid must be considered and
proper precautions taken.
CAUTION
7.2 Bushing Removal
The bushing (12) is press fit into the bonnet and does not normally
require replacement. If necessary, it may be pulled or machined
out. When machining the bushing out, care must be taken to
maintain proper dimensions and tolerances in the bonnet. These
will be furnished upon request.
7.3 Lapping Seats
Lapping is the process of working the valve plug against the
seat ring with an abrasive to produce a close fit. If valve leakage
is excessive, lapping becomes necessary. The plug and seat
ring seating surfaces should be free of large scratches or other
defects, and the contact surfaces of the seats should be as
4 | Baker Hughes
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narrow as possible. This may require dressing both parts in a
lathe. The seating surface angle of the plug is 28 degrees and
the seat ring is 30 degrees (relative to the centerline axis). A
good grade of fine grinding compound is required for the lapping
operation.
The compound should be mixed with a small quantity of lubricant
such as graphite. This will slow the cutting rate and prevent
tearing of the seating surfaces. The amount of lapping required
depends on the materials, condition of seating surfaces, and
accuracy of machining. lf a short period of lapping does not visibly
improve seating, there is usually no advantage in continuing as
excessive lapping may result in rough seats. The only remedy is
WARNING
replacement or re-machining of one or both parts. When lapping
new plugs and seat rings, begin with a medium fine (240 grit) and
finish with a finer grade (600 grit).
Note: Lapping should produce a line contact area, not the
entire surface, due to the difference in seat angles.
CAUTION
Before lapping, the plug and stem sub-assembly must
be concentric. (See pinning operation, section 7.5).
7.3.1 Threaded Trim (Figure 12 or 14)
CAUTION
1.
CIean body gasket surface areas.
2.
When seat has been removed, ensure that the sealing
surface in the body bridge and the threads are thoroughly
cleaned.
WARNING
Note: A sealant compatible with the process should be
applied sparingly to the seat ring threads and sealing
shoulder.
3.
lnstall and tighten seat ring using fabricated wrench used for
removal.
CAUTION
Do not over-tighten. Do not strike seat ring lugs
directly. This could distort the seat ring resulting in
seat leakage.
CAUTION
4.
Apply lapping compound on the plug at several spots equally
spaced around the seating area.
WARNING
5.
lnsert the stem and plug sub-assembly carefully into the
body until it is seated.
6.
Place bonnet (8) on the body and fasten the bonnet to the
body using four body stud nuts (10) spaced equally apart.
Apply slight pressure and tighten evenly.
CAUTION
Do not tighten nuts to final torque specifications at
this time. The bonnet is used temporarily for guiding
purposes only.
CAUTION
7.
lnsert two or three pieces of packing (6) into the packing box to
assist in guiding the stem and plug during lapping.
8.
Screw a drilled and tapped rod with a T-handle onto the plug
stem and secure with a locknut (see Figure 4).
Note: As an alternative, drill a hole through a flat steel
plate and fasten to the plug stem using two locknuts.
Copyright 2023 Baker Hughes Company. All rights reserved.
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