5
4. Lapping Procedure
(For metal seats only; does not apply to a-ring seat seal valve)
1. The finish on the body seat and disc are critical to seat
tightness. After the parts have been cleaned both parts
should be lapped to remove all blemishes and score
marks. This can be done on an automatic lapping
machine or by hand using a cast iron lapping block or
Pyrex lapping glass which is known to have a perfectly
flat surface.
that has been lapped off from the body seat in order to
maintain the critical parts respective relationship.
5b. (1890/95/96M only) Remove the same thickness of
material from the bottom face of the guide as that has
been lapped off from the body seat.
PYREX LAPPING PLATES:
PART NO.
MAT. CODE
SIZE
THICKNESS
6. Carefully clean compound from all parts. Failure to do so
may foul the seat and disc surfaces. When reinstalling
the parts in the valve and/or in assembling the disc in the
guide, be careful not to scratch or score either surface.
7688
7689
164
164
1-1;2'
2-1f4-
1;4"
%"
7. Check Appendix A for critical seat dimensions. Replace
any parts that have dimensions smaller than the minimum
required.
2. Use Farris 1200 lapping compound. When lapping the
disc, operate with a light figure eight motion over entire
block surface. In this way complete contact will be made.
With this motion the complete surface of the part will be
evenly lapped and you will avoid wearing a groove in the
block.
3. Lap the disc until all blemishes and score marks have
been removed. As the figure eight motion is executed,
frequently lift the disc away from the block to get a fresh
bite on the compound. Most importantly, do not contam-
inate compounds with dirt. Store lapping blocks and lap-
ping glass in a clean, dust-free area.
4. Measure and record the body seat height. Follow the
same procedure for lapping the body seat. When lapping
bodies the body can be placed on a table and a lapping
block placed on the body. Be sure that the lapping block
does not tip over the side of the body (which would cause
rounding of the edges). Use a light, rapid figure eight
stroke, lifting the block from the body occasionally.
5a. (1850/55/56M only) Remove the same thickness of
material from the bottom face of the blowdown ring as
TELEDYNE FLUID SYSTEMS
Farris Engineering
Visit www.boighill.com to request a quote.
Visit www.boighill.com to request a quote.
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