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10. Apply slight pressure on the stem, and rotate the stem in
short oscillating strokes (around 8 to 10 times). Repeat this
step as necessary.
Note:
The plug should be lifted and turned 90° each
time before repeating Step (10). This intermittent lifting
is required to keep the plug and seat ring concentric
during lapping.
11. After completion of the lapping operation, remove bonnet
and internal parts. The seating area of the seat ring and the
plug must be cleaned of all lapping compound in preparation
for reassembly.
7.4 Lo-dB PIug (Figure 8, 14 or 15)
The procedures used for performing maintenance on a valve
equipped with Lo-dB plugs (21700/21800/21900 Series) are the
same as those used for Threaded or Quick Change Trim.
CAUTION
CAUTION
WARNING
DANGER
Maintenance of the plug should be limited to cleaning
of the ports and the procedures defined under
Sections 7.3 (Lapping) and 7.5 (Pinning) as required.
7.5 PIug Stem Pinning
Plug stem pinning in the field may be required for the following:
- Replacing existing plug and stem, or
- Replacing existing stem only
Replacing Plug and Stem
If it is necessary to replace the plug, then the plug stem must be
replaced at the same time. The original pin hole in an existing
stem will not provide the necessary fit, and might seriously impair
the strength of the assembly.
A. Reference Marking on the Plug Stem
Measure the depth of the pilot recess in the plug (Dimension
X in Figure 9), and make a reference mark on the plug stem
at the same distance from the thread.
Note:
While pinning is being performed, care must
be taken not to damage the seating surface or plug
guide. Always use a soft metal or plastic vice jaws with
cylindrical features to hold the plug guide area (see
Figure 9).
B. Screwing Stem to Plug
•
Hold the plug (with vise jaw assembly) in a vise.
•
Lock two nuts against each other on the end of the new
plug stem, and screw the stem
solidly
into the plug using
a wrench on the upper nut.
When properly assembled, the reference mark (see
Section A above) should be flush with the end of the plug
guide.
C. Drilling the New Parts
•
If the plug is already fully drilled
(typical for 440 C
hardened stainless steel material or solid Stellite or
Equivalent), then drill the stem to the same diameter
(Diameter C in Figure 9) as the plug shank hole.
9.
Apply slight pressure on the stem, and rotate the stem in
short oscillating strokes (around 8 to 10 times). Repeat this
step as necessary.
Note: The plug should be lifted and turned 90° each
time before repeating Step (9). This intermittent lifting
is required to keep the plug and seat ring concentric
during lapping.
CAUTION
CAUTION
WARNING
DANGER
Avoid over-lapping as this can cause damage to
the seating surface rather than improve leakage
performance.
10.
After completion of the lapping operation, remove bonnet
and plug. The seating area of the seat ring and the plug
must be cleaned of all lapping compound in preparation for
reassembly.
Do not remove seat ring.
7.3.2 Quick-Change Trim (Figure 13 or 15)
1. CIean body gasket surface areas.
2. Install a new seat ring gasket (15) and insert seat ring (14)
in the body.
Note: Gasket (15) is temporarily placed to hold the seat
ring during lapping.
It is imperative to use a new gasket or
a test part having the same geometrical characteristics
in order to ensure the correct position of the seat ring
during lapping. This gasket (or similar part) can be kept
after lapping for future use. The gasket used for lapping
must not be reused for the body reassembly.
3. Apply lapping compound at several spots equally spaced
around the seating area of the seat ring.
4. Insert the cage (13) into the body.
5. lnsert the stem and plug sub-assembly carefully into the
body until it is seated.
6. PIace bonnet (8) on the body.
CAUTION
CAUTION
WARNING
DANGER
Ensure that the seat ring (14), cage (13) and bonnet
(8) are properly aligned.
7. Fasten the bonnet to the body using four body stud nuts
(10) spaced equally apart. Apply slight pressure and tighten
evenly.
CAUTION
CAUTION
WARNING
DANGER
Do not tighten nuts to final torque specifications at
this time. The bonnet is used temporarily for guiding
purposes only.
8. Insert two or three pieces of packing into the packing box to
assist in guiding the stem and plug during lapping.
9. 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.
