Hydraulic Symbols
Symbol Rules
1. Symbols show connections, flow paths, and functions of components represented. They can
indicate conditions occurring during transition from one flow path arrangement to another.
Symbols do not indicate construction, nor do they indicate values, such as pressure, flow
rate, and other component settings.
2. Symbols do not indicate locations of ports, direction of shifting of spools, or positions of
actuators on actual components.
3. Symbols may be rotated or reversed without altering their meaning, except in the cases of:
• lines to tank
• vented manifold
• accumulator
4. Symbols are shown in the following categories of function:
• lines and conductors
• fluid storage and energy storage
• fluid conditioners
• rotary devices
• valves
• actuators
• cylinders
• instruments and accessories.
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Hydraulic Symbols
Lines and Conductors
Item Symbol
High pressure and return lines
Drain and pilot lines
Component outline
Separate lines
Connected lines
or
Quick connect/disconnect
lines
or
Orifice
Adjustable orifice
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Hydraulic Symbols
Fluid Storage and Energy Storage
Item Note Symbol
Hydraulic tank or reservoir Main hydraulic tank usually
equipped with strainer in filler
neck, suction strainer before pump
inlet, and breather or pressurized
tank cap. or
Accumulator Piston or bladder type.
Pre-charged with dry nitrogen.
Abbreviation is “ACC”, or
“ACCUM.
Fluid Conditioners
Item Symbol
Filter with internal bypass check
valve
Filter with internal by-pass check
valve, and service indicator
Cooler
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Hydraulic Symbols
Item Symbol
Breather (mounted on reservoir)
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Hydraulic Symbols
Rotary Devices
Item Symbol
Hydraulic pump,
fixed displacement
Hydraulic pumps,
tandem installation
Hydraulic pump,
variable displacement
Hydraulic pump,
pressure compensated
Hydraulic motor,
fixed displacement
Pump/motor
Hydraulic motor, variable
displacement
Hydrostatic pump/motor,
dual direction, variable
displacement
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Hydraulic Symbols
Item Symbol
Radiator fan motor
Direction of rotation
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Hydraulic Symbols
Valves
Item Note Symbol
Check valve Allows flow in one direction only.
Ball side is direction of flow.
Spring-loaded check valve Fixed pressure setting.
Shuttle valve Pressure displaces ball in direction
of least resistance to block one port.
or
Typical control valve spool. Open centre, with hydraulic pilot.
Three position, four way.
Shut off valve Also known as “tow valve” on EJC
61 hydraulic schematic.
Adjustable relief valve Protects components in circuit from
excess pressures.
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Hydraulic Symbols
Item Note Symbol
Pressure reducing valve Limits pressure in one portion of
(adjustable). the circuit, i.e. pilot controls
(valve).
Abbreviation is “PRV”.
Typical double accumulator Controls hydraulic pressure in
charging valve brake circuit.
Port “A” may also be labelled
“ACC”.
Contains serviceable filter.
PRV interrupt, or auto brake valve. Solenoid valve.
PRV prevents pressure to pilot
valve during shutdown.
Auto brake activates park/
emergency brake.
Typical pilot valve Commonly used with directional
control valves.
Flow control valve (adjustable) Commonly used to fine tune
hydraulic controls, i.e. steering.
Typical park/emergency brake Causes park/emergency brake to
solenoid valve apply when de-energized.
In machines equipped with “LCB”
(Hydraulic Apply, Spring Release)
brakes.
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Hydraulic Symbols
Item Note Symbol
Brake pedal valve, posi-stop Spring apply, hydraulic release
brakes.
Typical brake pedal valve, “LCB” Hydraulic apply, spring release
brakes.
Cam operated valve Two position, four way valve.
Amplifier valve Ensures constant pressure in steer
circuit of EJC 20 truck.
Orbitrol valve Optional steering wheel, EJC 20
truck.
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Hydraulic Symbols
Actuators
Item Symbol
Manual
Push pull lever
Mechanical
Push button
Mechanical, spring
Pedal or treadle
Detent
Pilot pressure,
remote supply
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Hydraulic Symbols
Item Symbol
Pilot, hydraulic
Internal supply
Cam (mechanical)
Electric
Electric or hydraulic
Electric over hydraulic
Park brake actuator
“LCB” wheel end brake
(hydraulic apply, spring release)
“Posi-Stop” wheel end brake
(spring apply, hydraulic release)
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Hydraulic Symbols
Item Symbol
Engine actuator or throttle control
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Hydraulic Symbols
Cylinders
Item Note Symbol
Single acting cylinder Steer, boom, bucket and optional
eject cylinder.
Double acting cylinder Telescopic, two stage dump
cylinder.
Optional remote retrieval cylinder. Used as a towing aid.
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Hydraulic Symbols
Instruments and Accessories
Item Note Symbol
Pressure switch Actuates solenoid valve. See
electrical schematic. Abbreviation
“PSW”. or “PS”.
Differential pressure switch On machines equipped with
hydraulically applied brakes.
Abbreviation “DIFF.”
Pressure gauge
Temperature gauge
Test port Follow pressure test procedure.
or
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