Keep a check on the working surface of
Coils, rings, and corrugated ribbon are the
common forms of packing used in valves. The
the lap. If a groove develops, have the lap
form of packing to be used in repacking a
refaced.
particular valve will depend on the valve size,
Always use clean compound for lapping.
application, and type. Packing materials will be
discussed in tnore detail later in this chapter.
Replace the compound frequently.
Spread the compound evenly and lightly.
STEAM TRAPS
Steam traps are installed in steam lines to drain
Do not lap more than is necessary to
condensate from the lines without allowing the
produce a smooth even seat.
escape of steam. There are many different designs
of steam traps; some are suitable for high-pressure
Always use a fine grinding compound to
use and others for low-pressure use.
finish the lapping job.
TYPES OF STEAM TRAPS
Upon completion of the lapping job, spot-
in and grind-in the disk to the seat.
Some types of steam traps that are used in the
Navy are the mechanical steam traps, bimetallic
You should use only approved abrasive
steam traps, and orifice-type steam traps.
compounds for reconditioning valve seats and
disks. Compounds for lapping valve disks and
Mechanical Steam Traps
seats are supplied in various grades. Use a coarse
grade compound when you find extensive
Mechanical steam traps in common use in-
corrosion or deep cuts and scratches on the disks
clude bucket-type traps and ball-float traps.
and seats. Use a medium grade compound as a
The operation of the bucket-type steam trap,
follow-up to the coarse grade; you may also use
shown in figure 6-17, is controlled by the
it to start the reconditioning process on valves that
are not too severely damaged. Use a fine grade
compound when the reconditioning process nears
completion. Use a microscopic-fine grade for
finish lapping and for all grinding-in.
Refacing Valves
Badly scored valve seats must be refaced in
a lathe, with a power grinder, or with a valve
reseating machine. However, the lathe, rather
than the reseating machine, should be used for
refacing all valve disks and all hard-surfaced valve
seats. Work that must be done on a lathe or with
a power grinder should be turned over to shop
personnel.
Repacking Valves
If the stem and packing of a valve are in good
condition, you can normally stop packing gland
leaks by tightening up on the packing. You must
be careful, however, to avoid excessive thread
engagement of the packing gland studs (if used)
and to avoid tightening old, hardened packing
which will cause the valve to seize. Subsequent
operation of such a valve may score or bend the
stem.
Figure 6-17.--Bucket-type steam trap.
6-13
