Consolidated 13900 Series POSRV Maintenance Manual
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17
© 2018 Baker Hughes, a GE company. All rights reserved.
Reconditioning of the seat surface of the disc and base is
accomplished by lapping with a flat cast iron ring lap coated
with Grade No. 1000 KWIK-AK-SHUN Silicon-Carbide
compound, or equivalent. A 2.125" (54 mm) diameter lap
should be used.
To recondition the disc seal by lapping, it is necessary to
disassemble the disc assembly. This is done in the following
manner: referring to Figure 8 and Table 4, the disc is
contained in the disc holder by a Truarc retaining ring. The
ring may be removed using a Truarc Plier, BHGE Part No.
5153302, after removing the Truarc ring, the disc collar can
be removed from the disc holder.
Lapping a flat seal is simple. No special skill is required and
the technique is readily apparent after a few minutes of
actual lapping.
The following precautions and hints will enable anyone to do
a professional job of lapping seats.
1. Keep the work clean.
2. Always use a fresh lap. If Signs of wearing (out of
flatness) are evident, recondition the lap.
3. Apply a very thin layer of compound to the lap. This will
prevent rounding off the edges of the seat.
4. Keep the lap squarely on the flat seat and avoid any
tendency to rock the lap which will cause rounding of
the seat.
5. When lapping, keep a firm grip on the lap to prevent the
possibility of dropping it and damaging the seat.
6. Lap, using a reciprocating motion in all directions, at the
same time applying light uniform pressure and rotating
the lap slowly.
7. Replace the compound frequently after wiping off the
old compound, and apply more pressure to speed the
cutting action of the compound.
8. To check the seating surfaces, remove all compound
from both the seat and the lap. Then shine up the seat
with the same lap using the lapping motion described
above. Low sections on the seating surface will show up
as a shadow in contrast to the shiny portion. If shadows
are present, further lapping is necessary, and only laps
known to be flat should be used. Only a few minutes
will be required to remove the shadows.
9. When the lapping is completed, any lines appearing
as cross scratches can be removed by rotating the lap,
which has been wiped clean of compound, on the seat
about its own axis.
10. The seat should now be thoroughly cleaned with
alcohol, using a lint-free cloth or tissue paper.
11. When the seats cannot be repaired by lapping, they
can be machined in accordance with the following
instructions. Refer to Figures 8 to 11.
a) Using a four-jaw chuck, align the disc or base by
indicating at A and B. Runout as A or B cannot
exceed .001” (0.03 mm).
b) Take light cuts across Disc Seat “C” (Figure
10) to remove defects and restore 32 RMS
finish. Dimensions F and G must be maintained
(Figure 8) and dimension .028” (0.71 mm) must be
reestablished. When “M” dimension (Figure 8) has
been reduced to .284” (7.21 mm), the disc should
be replaced.
c)
Take light cuts across Pilot Nozzle Seat “C” (Figure
11), to remove defects and restore 32 RMS finish.
Dimensions A, B and C must be maintained
(Figure 9) and the seat step dimension .028” (0.71
mm) must be reestablished (Figure 9). When "D"
dimension is reduced below minimum specified
(Figure 10), the base should be replaced.
d) Lap the seats. Refer to steps 1 through 10 of
“Pilot Valve Seat Repairing and Lapping”, which
precedes step 11 above.
XIII. Inspection and Part Replacement
