Service Manual

3.4297.4
3.4297.409
I I
Productivity Series
Directional Valves are used to control the
direction or path of fluid flow in a hydraulic
system. This may consist of a check valve
preventing backflow through a line or a spool
valve diverting the fluid’s path to a remote
cylinder.
Flow Control valves are used to regulate flow
into or out of a hydraulic component.
With a lift cylinder, a flow control valve can
control the rate at which oil enters or leaves the
cylinder. This allows the speed at which the
cylinder extends or retracts to be regulated.
With a transaxle, a flow control valve may
restrict flow through a passage completely
during normal operation, but when activated,
allow oil to pass through
so the unit can be hand
pushed.
Valves By Name
Acceleration Valve
An acceleration valve is a
special flow control valve used in some
hydrostatic transmissions to smooth changes in
speed or direction.
A common way to do this is
by temporarily allowing some oil to escape from
the high pressure side to the low pressure side
of the pump/motor circuit.
One example of an acceleration valve uses a
small metering hole which slowly allows high
pressure oil to enter the cavity behind the valve.
As the cavity is filled, the valve advances and
closes the passage between the high and low
pressure circuits.
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