reseating machine. With a fine file, remove all high
spots on the surface of the flange upon which the chuck
jaws must fit. Note that a valve reseating machine can
be used ONLY with a valve in which the inside of the
bonnet flange is bored true with the valve seat. If this
condition does not exist, the valve must be reseated in
a lathe and the inside flange bored true.
Before placing the chuck in the valve opening,
open the jaws of the chuck wide enough to rest on the
flange of the opening. Tighten the jaws lightly, so the
chuck grips the sides of the valve opening securely.
Tap the chuck down with a wooden mallet until the
jaws rest on the flange firmly and squarely. Then
tighten the jaws further.
Adjust and lock the machine spindle in the cutting
position and begin cutting by turning the crank slowly.
Feed the cutter slowly, so very light shavings are
taken. After some experience, you can tell whether or
not the tool is cutting evenly all around. Remove the
chuck to see if enough metal has been removed.
Be sure the seat is perfect. Then remove the
45-degree cutter and face off the top part of the seat
with a flat cutter. Dress the seat down to the proper
dimensions as follows:
Width of Seat
Size of Valve
l/4 to 1 inch
1 l/4 to 2 inches
2 l/2 to 4 inches
4 l/2 to 6 inches
After the refacing, grind-in the seat and disk.
Spot-in as necessary to check the work. A rough
method of spotting-in is to place pencil marks at
intervals of about l/2 inch on the bearing surface of
the seat or disk. Then place the disk on the seat and
rotate the disk about a quarter of a turn. If the pencil
marks in the seating area rub off, the seating is
Repacking Valve Stuffing
When the stem of a globe valve is in good
condition, stuffing box leaks can usually be stopped
by setting up on the gland. If this does not stop the
leakage, repack the stuffing box. The gland must not
be set up or packed so tightly that the stem binds. If
the leak persists, a bent or scored valve stem may be
the cause of the trouble.
Coils (string) and rings are the common forms of
packing used in valves. The form to be used in a
particular valve is determined, in part, by the size of
the packing requi red. In general, rings are used in
valves that require packing larger than 1/4 inch. When
a smaller size is required, string packing is used.
When you repack a valve stuffing box, place
successive turns of the packing material around the
valve stem. When string packing is used, coil it around
the valve stem. Bevel off the ends to make a smooth
seating for the bottom of the gland. Then put on the
gland and set it up by tightening the bonnet nut or the
gland bolts and nuts. To prevent the string packing
from folding back when the gland is tightened, wind
the packing in the direction in which the gland nut is
to be turned. Usually, where successive rings are used,
the gaps in the different rings should be staggered.
Gate, globe, angle, and stop-check valves are
made to back seat the stem against the valve bonnet
when the valve is fully opened. Back seating of these
valves is a safety feature to eliminate the stem being
forced out under pressure while the valve is fully
opened. Back seating makes repacking of the stem
stuffing box possible under pressure; however, you
should attempt this only in emergencies and with
What structure of a valve distinguishes one type
of valve from another?
Direction of flow is indicated on the exterior of
a check valve in what manner?
Hydraulic control valves are used in what type
of plumbing system?
To reface valves, you can use the valve reseating
machine only when what condition exists?
LEARNING OBJECTIVE: Recognize the
different types of valve accessories and the
methods used to maintain them.
Accessories that aid in the control of valves
include valve boxes, floor stands, and post indicators.
Each of these supporting materials is discussed briefly
Street valves must be accessible for turning them
off and on; and, with large valves, the entire valve
should be accessible for servicing. Since valves are
placed at various depths, valve boxes are made in two