Figure 13-6.--Typical seawater ball valve.
an integral part of the valve body. In view B, the seating
surface has been welded so that it has become an
Figure 13-7.--Typical ball stop swing-check valve for seawater
integral part of the seat ring. The seat ring is threaded
service.
into the body and then seal-welded. If you must renew
the seating surface of A, you need only machine away
the existing weld material and then rebuild the seating
handwheel to completely open or close the valve.
surface with successive deposits of new weld material.
Others are operated by planetary gears that use a
Then you can machine a new seating surface. If you
relatively small handwheel and opening force to operate
must renew the seating surface shown in view B, first
a fairly large valve. The gearing does, however, increase
machine the seal weld from the ring and remove the ring
the time needed to open and close the valve. Some ball
from the valve body. You may then either install a new
valves have a swing-check located within the ball to
seat ring or remove, rebuild, and machine the existing
give the valve a check valve feature. Figure 13-7 shows
seat surface.
a ball stop swing-check valve with planetary gear
After you have completed the machining, spot-in,
operation. Ball valves are normally found in the
and lightly grind-in the seat and disk. Then respot the
following systems aboard ship: seawater, sanitary, trim
seat and disk to be sure contact between the two is as it
and drain, air, hydraulic, and oil transfer. Portsmouth
should be.
Process Instruction 4820-921-339D contains repair
procedures for ball valves. In the smaller types, you will
Repairing Ball Valves
normally replace parts rather than machine and rebuild
them.
Ball valves, as the name implies, are stop valves that
use a ball to stop or start the flow of fluid. The ball,
disk in a globe valve. When you turn the handwheel to
Gate valves answer a need for a straight line flow
open the valve, the ball rotates to a point where the hole
of fluid with minimum flow restriction. Gate valves are
through the ball is in line with the valve body inlet and
so named because the part (gate) that either stops or
outlet. When you shut the valve, the ball rotates so the
allows flow through the valve acts somewhat like the
hole is perpendicular to the flow openings of the valve
opening or closing of a gate. The gate is usually
body, and the flow stops.
wedge-shaped. When the valve is wide open, the gate
Most ball valves are the quick-acting type; they
is fully drawn up into the valve. This leaves an opening
require only a 90-degree turn of a simple lever or
for flow through the valve that is the same size as the
13-7