spring-loaded poppet, a cage, and a stainless steel filter
then has a free flow to the unit outlet port, but is
prevented from entering the normal system by the
element.
shuttle.
The one-way restrictor allows free flow in one
direction and restricted flow in the opposite direction.
Maintenance of Shuttle Valves
Arrows found on the body of the valve indicate both
directions of flow.
Shuttle valve maintenance is generally limited to
repairing leakage. Tightening the end caps may
In a restricted direction, pressurized fluid entering
generally repair external leakage. If this does not stop
port R (fig. 11-16) flows through the filter assembly
excessive leakage, the end cap O-rings should be
and enters the cage through drilled passages. Fluid
replaced.
from the interior of the cage is forced through the
poppet's orifice, thus causing the required metering
Removing and flushing the unit with clean
action.
hydraulic fluid can usually repair internal leakage.
Excessive heating is a good indication of internal
In the free flow direction, pressurized fluid
leakage through a shuttle valve. Excessive cycling of
entering port F overcomes poppet spring tension and
the emergency system pump is also an indication of a
allows fluid to flow past the poppet's seat, through
leaky shuttle valve.
drilled passages within the larger flange of the cage,
and out through port R.
After an emergency system has been operated, all
emergency system pressure should be bled off as soon
Two-Way Restrictor
as possible, and the normal system restored to
operation.
Two-way restrictors are used to limit the flow of
hydraulic fluid where it is desirable to retard the action
RESTRICTORS
of a hydraulic cylinder in both directions. Figure 11-16
Restrictors are used in hydraulic systems to limit
shows two types of two-way restrictors, one of which
the flow of hydraulic fluid to or from actuators where
has a machined orifice with two integral stainless steel
speed control of the cylinders is necessary to provide
filters. The other type shown contains an orifice plate
specific actions. If control in one direction only is
between two stainless steel filters. The filters
desired, a one-way restrictor is used. If restricted fluid
contained within the restrictors are identical in
flow both to and from an actuating cylinder is
construction and provide protection in both directions
necessary, a two-way restrictor is installed.
of flow. The filter size specification for the two-way
restrictor is identical to those found within one-way
One-Way Restrictor
restrictors.
Two-way restrictors, regardless of whether they
One-way restrictors provide reduced hydraulic
are of the machined orifice type or of the plate orifice
flow in one direction only, to limit actuating speed of
type, operate identically. Fluid entering either port is
hydraulic cylinders for the purpose of proper timing or
filtered prior to flowing through the orifice, thus
sequence of operation. Also, they provide free flow of
protecting the orifice from possible stoppage. As the
fluid in the opposite direction to permit the actuating
fluid is metered through the orifice, the prescribed rate
cylinder to actuate at a faster rate of speed during the
reverse action of the cylinder.
flow is directed out the opposite port of the restrictor
and to the actuating unit.
One-way restrictors are used in some landing gear
systems to regulate the speed and sequence of landing
Maintenance of Restrictors
gear retraction or extension. If sequenced action (that
is, one cylinder to be actuated before other cylinders on
Maintenance of restrictors is usually limited to
the same line) is desired, one-way restrictors are placed
checking for external leakage and the required fluid
in the line upstream of all cylinders except one.
flow. The specific MIM lists the required fluid flow in
gallons per minute (gpm) for each size of orifice being
Figure 11-16 shows both the one-way and two-way
checked. It also specifies the correct pressures to use
restrictors. The main parts of a one-way restrictor are
as well as the required procedures during each check.
the cylindrical body and cap, which contain a
11-18
