the poppet spring, which causes the poppet to bottom
A typical shuttle valve is shown in figure 11-15.
and allows free flow of fluid through the valve.
The body contains three ports--the normal system
inlet port, the emergency system inlet port, and the unit
SHUTTLE VALVES
outlet port. A shuttle valve used to operate more than
one actuating cylinder may contain additional unit
All aircraft incorporate emergency systems that
outlet ports.
provide alternate methods of operating essential
Enclosed in the body is a sliding part called the
systems required to land the aircraft safely. These
shuttle. It is used to seal one of the two inlet ports. A
emergency systems usually provide pneumatic or
shuttle seat is installed at each inlet port. During
hydraulic operation of the essential systems; however,
operation, the shuttle is held against one of these seats,
in some cases due to the design, they may be operated
sealing off that port. These parts are held in the body
satisfactorily through mechanical linkage. When you
by end caps. An O-ring gasket at each end cap prevents
use the pneumatic or hydraulic emergency system, that
external leakage.
pressure must be directed to the unit concerned;
emergency pressure must not enter the normal system,
Operation of Shuttle Valves
especially if the pneumatic type system is used. To
allow operating pressure to reach the actuating unit and
When a shuttle valve is in the normal operating
still not enter the other system, a shuttle valve is
position, fluid has a free flow from the normal system
installed in the working line to the actuating unit. The
inlet port to the unit outlet port. The shuttle is seated
main purpose of the shuttle valve is to isolate the
against the emergency inlet port, and held there by the
normal system from the emergency system.
shuttle spring or by normal system pressure. The
Shuttle valves are located close to the actuating
shuttle remains in this position until the emergency
unit concerned. This location reduces to a minimum
fluid, gas, or air is released under pressure by the
the units to be bled and isolates as much of the normal
e m e rg e n cy c o n t r o l va l ve . T h e a p p l i c a t i o n o f
system from the emergency system as possible. In
emergency pressure at the emergency inlet port forces
some installations, the shuttle valve is an integral part
the shuttle from the emergency inlet port seat to the
of the actuating unit.
normal system inlet port seat. The emergency pressure
Figure 11-15.--Shuttle valve.
11-17
