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Section II – Description
A. General
Directional valves are devices used to change the flow
direction of fluid within a hydraulic circuit. A valve is
designed to control the direction of movement of a work
cylinder or the direction of rotation of a fluid motor.
B. Basic Four-Way Sliding Spool
Directional Valve Construction
Vickers valve bodies have a precision machined bore in
which a very close tolerance spool is suspended on a film of
hydraulic fluid. Spool lands and body cavities are designed
to divide the bore openings into separate chambers. Ports in
the body lead into these chambers so that spool position
determines which ports are open or closed. See Figure 1. Oil
flow is directed from one port to another within the body and
out of a port to the work.
C. Two Stage Directional Valve
Construction
Two stage directional valves are pilot pressure operated. A
two stage valve is constructed by combining a pilot valve
and a larger main stage valve into one assembly. The pilot
valve, usually a DG4S4-01, DG4V-3 or DG18V-3 is mounted
on top of the main stage valve. The pilot valve controls spool
movement within the main stage section. Pilot spool
movement is normally, actuated by electrical solenoids.
When a solenoid is energized (activated), the pilot spool
moves and fluid is diverted to the main stage; thus
controlling main stage spool movement, Figure 2 illustrates
the basic construction of a two stage, pilot operated
directional valve.
Figure 1. Spool Type Four-Way Valve
A
Pressure to “B”
“A” to Tank
B
A
B
A
B
T
T
P
Pressure to “A”
“B” to Tank
T
P
T
P
Figure 2. Typical “DG5” Type Solenoid Controlled, Pilot Operated Valve
1. This pilot stage
spool controls the
pilot pressure which
2. can be directed to
either end of the
main stage spool.
External Pilot
Drain Port
Manual override to
shift pilot stage
mechanically when
troubleshooting
Internal Pilot
Drain Port
