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8/13/2019 Directional Control
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PowerPointPresentation
Chapter 5
Directional Control
Check Valves Directional ControlValves Directional Control Valve
Actuators Logic Valves
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Chapter 5Directional Control
A restriction check valve
has an orifice placed in
the center of the poppet
to permit restricted fluid
flow through the valve inthe NC position.
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Chapter 5Directional Control
A pilot-to-open check
valve allows fluid flow in
one direction and stops
fluid flow in the opposite
direction until it receivesa pressure signal through
a pilot line applied to the
piston port.
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Chapter 5Directional Control
A pilot-to-open check valve is often used to hold a
double-acting cylinder in place when the cylinder has a
load suspended on it.
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Chapter 5Directional Control
A pilot-to-close check valve allows fluid flow in
one direction until the pilot signal is sent to close
the valve.
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Chapter 5Directional Control
The primary function of a directional control valve is
to direct or prevent fluid flow to specific piping or
system actuators.
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Chapter 5Directional Control
A schematic diagram can be used to determine the
operating characteristics of a directional control valve.
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Chapter 5Directional Control
A way is the number
of valve ports, and
position is the
number of different
positions that a spoolof a directional
control valve is
capable of moving
into in a directionalcontrol valve.
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Chapter 5Directional Control
In a schematic diagram,
internal arrows inside the
position boxes depict the
direction of fluid flow for
each spool position.
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Chapter 5Directional Control
Naming standards include the number of positions,
the number of ways, the types of directional control
valve actuators, and the normal spool center position.
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Chapter 5Directional Control
Two-position,
two-way
directional
control valves
can turn on andoff separate
hydraulic
systems that are
powered by thesame hydraulic
power unit.
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Chapter 5Directional Control
A two-position,
three-way
directional control
valve has two
positions, one toallow fluid flow from
the cylinder port to
the tank port and
the other to allowfluid flow from the
pump to the
cylinder port.
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Chapter 5Directional Control
Two-position, four-way
directional control valves
are typically used to
control cylinders that lift
heavy loads.
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Chapter 5Directional Control
An advantage of three-position, four-way directional
control valves is that they have four different center
positions that can perform four different operations.
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Chapter 5Directional Control
Open-center positions are typically used in
applications where there is only one cylinder in the
hydraulic system.
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Chapter 5Directional Control
When using a closed-
center position, fluid flow
created by a variable-
displacement, pressure-
compensated pumpeither goes through a
relief valve or is
automatically reduced to
no flow.
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Chapter 5Directional Control
Tandem-center positions are used to hold a cylinder in
the desired position while allowing fluid flow to be
directed back to the tank without the need to activate a
relief valve.
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Chapter 5Directional Control
Float-center positions allow a the piston in a cylinder to
move while it is in the center position and can still
direct fluid flow back to the tank.
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Chapter 5Directional Control
Subplate mounting
allows for a directional
control valve to be
mounted to a plate that
attaches directly tosystem piping.
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Chapter 5Directional Control
Spring actuators are
used to shift the spool of
a directional control valve
to normal position.
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Chapter 5Directional Control
A pilot pressure actuator
uses fluid pressure to
actuate a directional
control valve spool.
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Chapter 5Directional Control
Directional control valves
can be single- or double-
solenoid actuated.
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Chapter 5Directional Control
When shifting is required, fluid flow from a piggyback
valve is directed as pilot pressure to either side of the
main directional control valve spool.
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Chapter 5Directional Control
A pilot choke is mounted between a main valve and a
pilot valve that is used to slow or briefly delay
reversals in spool movement.
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Chapter 5Directional Control
A pilot piston allows a directional control valve spool
to shift quickly by placing the pilot piston in a pilot-
pressure chamber near the spool in the main valve.
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Chapter 5Directional Control
A detent operates by locking the spool in a desiredposition and not allowing it to move back into its
normal position until it is manually repositioned.
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Chapter 5Directional Control
In an ANDhydraulic circuit,
pressure must
be present from
the hydraulicsystem (input 1)
and through the
pilot line (input
2) before the
cylinder (output)
can operate.
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