reseating machine. With a fine file, remove all high
Coils (string) and rings are the common forms of
spots on the surface of the flange upon which the chuck
packing used in valves. The form to be used in a
jaws must fit. Note that a valve reseating machine can
particular valve will be determined, in part, by the size
be used ONLY with a valve in which the inside of the of the packing required. In general, rings are used in
bonnet flange is bored true with the valve seat. If this
valves that require packing larger than one-fourth inch.
condition does not exist, the valve must be reseated in
When a smaller size is required, string packing is
a lathe, and the inside flange bored true. generally used.
Before placing the chuck in the valve opening, open
When you repack a valve stuffing box, place
the jaws of the chuck wide enough to rest on the flange
successive turns of the packing material around the
of the opening. Tighten the jaws lightly so that the chuck
valve stem. When strong packing is used, coil it around
securely grips the sides of the valve opening. Tap the
the valve stem. Bevel off the ends to make a smooth
chuck down with a wooden mallet until the jaws rest
seating for the bottom of the gland. Then put on the
firmly and squarely on the flange. Then tighten the jaws
gland and set it up by tightening the bonnet nut or the
further.
gland bolts and nuts. To prevent the strong packing from
folding back when the gland is tightened, wind the
Adjust and lock the machine spindle in the cutting packing in the direction in which the gland nut is to be
position and start the cutting by turning slowly on the turned. Usually, where successive rings are used, the
crank. Feed the cutter slowly so that very light shavings gaps in the different rings should be staggered.
are taken. After some experience, you will be able to
know by the feel whether or not the tool is cutting evenly
Gate, globe, angle, and stop check valves are made
all around. Remove the chuck to see if enough metal has
to back seat the stem against the valve bonnet when the
been removed.
valve is fully opened. Back seating of these valves is a
safety feature to eliminate the possibility of the stem
Be sure the seat is perfect. Then remove the being forced out under pressure while the valve is fully
45-degree cutter and face off the top part of the seat with opened. Back seating makes possible the repacking of
a flat cutter. Dress the seat down to the proper the stem stuffing box under pressure. However, you
dimensions, as follows: should attempt this only in emergencies and with
extreme caution.
Width of Seat Size of Valve
1/16 inch 1/4 to 1 inch
GATE VALVES
3/32 inch 1 1/4 to 2 inches
1/8 inch 2 1/2 to 4 inches
The manner in which a gate valve is used has a great
deal to do with its service life. Gate valves should
3/16 inch 4 1/2 to 6 inches
always be used either wide open or fully closed; never
in a partially opened position. When a gate valve is
After the refacing, grind-in the seat and disk.
partly open, the gate is not held securely, but swings
Spot-in as necessary to check the work. A rough method
back and forth with the pulsation of the flow. As the gate
of spotting-in is to place pencil marks at intervals of
swings, it strikes the valve body and the finished
about one-half inch on the bearing surface of the seat or
surfaces, nicking and scoring them. When these
disk. Then place the disk on the seat and rotate the disk
surfaces are imperfect, the valve gate cannot set
about a quarter of a turn. If the pencil marks in the
accurately and seal off the flow. A gate valve should
seating area rub off, the seating is considered
never be installed in any position where a throttling or
satisfactory.
flow-regulating valve is required. A globe valve should
be used in those situations.
Repacking Valve Stuffing Boxes
Lapping is the best way to correct gate valve defects
such as light pitting or scoring and imperfect seat
If the stem of a globe valve is in good condition, contact. The lapping process is basically the same for
stuffing box leaks can usually be stopped by setting up gate valves as it is for globe valves. The exception is
on the gland. If this does not stop the leakage, repack that the lap is turned by a handle that extends through
the stuffing box. The gland must not be set up or packed the end of the valve body. Remove the valve from the
so tightly that the stem binds. If the leak persists, a bent system. Insert the lapping tool, without its handle, into
or scored valve stem may be the cause of the trouble. the valve so that it covers one of the seat rings. Then
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