through the shuttle and sleeve assembly. Subsystem
pressurized fluid works on the large flange area of the
shuttle, which causes the shuttle to move to the left
after reaching a specified pressure, thus closing off
the normal system.
The valve will stay in this
position until the subsystem pressure is lowered, at
which time the shuttle will move to its prior position
and allow the required amount of pressurized fluid to
enter the subsystem. During normal operation of the
subsystem, the pressure-reducing valve continuously
meters fluid to the subsystem.
HYDRAULIC FUSES
A hydraulic fuse is a safety device. Fuses may be
installed at strategic locations throughout a hydraulic
system. They are designed to detect line or gauge
rupture, fitting failure, or other leak-producing failure
or damage.
One type of fuse, referred to as the automatic
resetting type, is designed to allow a certain volume
of fluid per minute to pass through it. If the volume
passing through the fuse becomes excessive, the fuse
will close and shut off the flow. When the pressure is
removed from the pressure supply side of the fuse, it
will automatically reset itself to the open position.
Fuses are usually cylindrical in shape, with an
inlet and outlet port at opposite ends, as shown in
figure 8-18. A stationary sleeve assembly is con-
tained within the body. Other parts contained within
the body, starting at the inlet port, are a control head,
piston and piston subassembly stop rod, a lock spring,
and a lock piston and return spring.
Fluid entering the fuse is divided into two flow
paths by the control head. The main flow is between
the sleeve and body, and a secondary flow is to the
piston. Fluid flowing through the main path exerts a
force on the lock piston, causing it to move away from
the direction of flow, This movement uncovers ports,
allowing fluid to flow through the fuse.
The movement of the locking piston also causes a
lock spring to release the piston subassembly stop
Figure 8-18.—Fuse, operational view.
8-22
