shuttle seat is installed at each inlet port. During
operation, the shuttle is held against one of these
seats, sealing off that port. These parts are held in the
body by end caps. External leakage is prevented by
an O-ring gasket at each end cap.
Operation of Shuttle Valves
When a shuttle valve is in the normal operating
position, fluid has a free flow from the normal system
inlet port to the unit outlet port. The shuttle is seated
against the emergency inlet port, and held there by the
shuttle spring or by normal system pressure. The
shuttle remains in this position until the emergency
fluid, gas, or air is released under pressure by the
emergency control valve. The application of
emergency pressure at the emergency inlet port forces
the shuttle from the emergency inlet port seat to the
normal system inlet port seat. The emergency
pressure then has a free flow to the unit outlet port,
but is prevented from entering the normal system by
the shuttle.
Maintenance of Shuttle Valves
Shuttle valve maintenance is generally limited to
repairing leakage. External leakage may generally be
repaired by tightening the end caps. If this does not
stop excessive leakage, the end cap O-rings should be
replaced.
Internal leakage can usually be repaired by
removing and flushing the unit with clean hydraulic
fluid. Excessive heating is a good indication of
internal leakage through a shuttle valve. Excessive
cycling of the emergency system pump is also an
indication of a leaky shuttle valve.
After an emergency system has been operated, all
emergency system pressure should be bled off as soon
as possible, and the normal system restored to
operation.
RESTRICTORS
Restrictors are used in hydraulic systems to limit
the flow of hydraulic fluid to or from actuators where
speed control of the cylinders is necessary to provide
specific actions. If control in one direction only is
desired, a one-way restrictor is used. If restricted
fluid flow both to and from an actuating cylinder is
necessary, a two-way restrictor is installed.
Figure 8-15.—Shuttle valve.
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