New Version of this page on Airline Hydraulic's website.

Basic Schematic Symbols (Hydraulic and Pneumatic)

Other Fluid Power Informational Links:

   Lines

-continuous line - flow line
-dashed line - pilot, drain
-envelope - long and short dashes around two or more component symbols.

   Circular

-large circle - pump, motor

-small circle  - Measuring devices

-semi-circle - rotary actuator

   Square

-one square  - pressure control function
-two or three adjacent squares  - directional control

   Diamond

-diamond - Fluid conditioner (filter, separator, lubricator, heat exchanger)

   Miscellaneous Symbols

-Spring
-Flow Restriction

   Triangle

-solid - Direction of Hydraulic Fluid Flow
-open - Direction of Pnematic flow

Pumps and Compressors


   Fixed Displacement hydraulic pump

Fixed Displacement hydraulic pump Schematic Symbol -unidirectional pump symbol
Fixed Displacement hydraulic pump (Reversible flow) Schematic Symbol -bidirectional pump symbol

   Variable displacement hydraulic pump

Variable displacement hydraulic pump Schematic Symbol -unidirectional pump symbol
Variable displacement hydraulic pump (Reversible flow) Schematic Symbol -bidirectional pump symbol

   Compressor

Compressor Schematic Symbol

Motors


   Fixed displacement hydraulic motor

Fixed displacement hydraulic motor Schematic Symbol -unidirectional
Fixed displacement hydraulic motor (Reversible/bidirectional) Schematic Symbol -bidirectional 

   Variable displacement hydraulic motor

Variable displacement hydraulic motor Schematic Symbol -unidirectional
Variable displacement hydraulic motor (Reversible/bidirectional) Schematic Symbol -bidirectional

   Pneumatic motor symbol (Air motor)

Pneumatic air motor Schematic Symbol -unidirectional
Pneumatic motor (Reversible/bidirectional)  Schematic Symbol -bidirectional

   Rotary Actuator symbol

Hydraulic Rotary Actuator Schematic Symbol - hydraulic
="Pneumatic - pneumatic

Cylinders


   Single acting cylinder

Single acting cylinder symbol (pilot return) Schematic Symbol -returned by external force
Single acting cylinder symbol (spring Return) Schematic Symbol -returned by spring or extended by spring force

   Double acting cylinders

Double acting cylinder symbol (single piston rod) Schematic Symbol -single piston rod (fluid required to extend and retract)
Double acting cylinder symbol (double ended piston rod) Schematic Symbol -double ended piston rod

   Cylinders with cushions

Cylinders with a single fixed cushion Schematic Symbol - single fixed cushon
Cylinders with a double fixed cushion Schematic Symbol - double fixed cushion
Cylinders with a single adjustable cushion Schematic Symbol - single adjustable cushion
Cylinders with a double adjustable cushion Schematic Symbol - double adjustable cushion

Directional Control Valve symbols


   Directional control valve (2 ports / 2 positions)

Normally closed, directional control valve with 2 ports and 2 finite positions (Schematic Symbol) -Normally closed directional control valve with 2 ports and 2 finite positions.
Normally open, directional control valve with 2 ports and 2 finite positions. (Schematic Symbol) -Normally open directional control valve with 2 ports and 2 finite positions.

   Directional control valve (3 ports / 2 positions)

Normally closed, directional control valve with 3 ports and 2 finite positions. (Schematic Symbol) -Normally closed directional control valve with 3 ports and 2 finite positions.
Normally open, directional control valve with 3 ports and 2 finite positions. (Schematic Symbol) -Normally open directional control valve with 3 ports and 2 finite positions.

   Directional control valve (4 ports / 2 positions)

directional control valve with 4 ports and 2 finite positions. (Schematic Symbol) -directional control valve with 4 ports and 2 finite postions

   Directional control valve (4 ports / 3 positions)

directional control valve with 4 ports and 3 finite positions. (Schematic Symbol) -directional control valve with 4 ports and 3 finite postions
*-(center position can have various flow paths)

   Directional control valve (5 ports / 2 positions) Normally a pneumatic valve

directional control valve with 5 ports and 2 finite positions. (Schematic Symbol) -directional control valve with 5 ports and 2 finite postions

   Directional control valve (5 ports / 3 positions) Normally a pneumatic valve

directional control valve with 5 ports and 3 finite positions. (Schematic Symbol) -directional control valve with 5 ports and 3 finite postions

   Proportional directional control valve

   Electro-hydraulic servo valve

   -The spool positions on these valves is variable allowing for variable flow conditions.

single-stage Electro-hydraulic servo valve, direct operation unit which accepts an analog signal and provides a similar analog fluid power output (Schematic Symbol) -single-stage direct operation unit which accepts an analog signal and provides a similar analog fluid power output
two-stage Electro-hydraulic servo valve with mechanical feedback indirect pilot operation unit which accepts an analog signal and provides a similar analog fluid power output (Schematic Symbol) -two-stage with mechnical feedback indirect pilot operation unit which accepts an analog signal and provides a similar analog fluid power output

Control Methods


   Manual Control

general symbol of a Valve's Manual Operator (without showing the control type) (Schematic Symbol) -general symbol (without showing the control type)
symbol for a pushbutton Valve's Operator (Schematic Symbol) -pushbutton
-lever
symbol for a foot pedal Valve's Operator (Schematic Symbol) -foot pedal

   Mechanical Control

symbol for a plunger Valve's Operator (Schematic Symbol) -plunger or tracer
symbol for a Valve with spring return on one side (Schematic Symbol) -spring
symbol for a roller Valve's Operator (Schematic Symbol) -roller
symbol for a roller Valve's (one direction only) type Operator (Schematic Symbol) -roller(one direction only)

   Electrical Control (Solenoid Valve symbol)

symbol for a Solenoid Valve's Operator (Schematic Symbol) -Solenoid (the one winding)

   Pilot Operation

symbol for a pneumatically actuated pilot Valve's Operator (Schematic Symbol) -pneumatic
symbol for a hydraulically actuated pilot Valve's Operator (Schematic Symbol) -hydraulic

   Pilot operated two-stage valve

symbol for a two-stage piloted (Pneumatic: Solenoid first stage) Valve's Operator (Schematic Symbol) -Pneumatic: Solenoid first stage
symbol for a two-stage piloted (Pneumatic: Air pilot second stage) Valve's Operator (Schematic Symbol) -Pneumatic: Air pilot second stage
symbol for a two-stage piloted (Hydraulic: Solenoid first stage) Valve's Operator (Schematic Symbol) -Hydraulic: Solenoid first stage
symbol for a two-stage piloted (Hydraulic: Hydaulic pilot second stage) Valve's Operator (Schematic Symbol) -Hydraulic: Hyd pilot second stage

Check valves, Shuttle valves, Rapid Exhaust valves


symbol for a Check Valve (Schematic Symbol) -check valve -free flow one direction, blocked flow in other direction
symbol for a pilot operated check valve, pilot to close (Schematic Symbol) -pilot operated check valve, pilot to close
symbol for a pilot operated check valve symbol, pilot to open (Schematic Symbol) -pilot operated check valve, pilot to open

   Shuttle valve

symbol for a shuttle valve (Schematic Symbol) -to isolate one part of a system from an alternate part of circuit.

   Rapid exhaust valve/Pneumatic

symbol for a (Pneumatic) Rapid exhaust valve (Schematic Symbol) -installed close to an actuator for rapid movement of the actuator.

Pressure Control Valves


   Pressure Relief Valve(safety valve) normally closed

symbol for a Pressure Relief Valve(safety valve) normally closed (Schematic Symbol) - line pressure is limited to the setting of the valve, secondary part is directed to tank.

   Proportional Pressure Relief

symbol for a Proportional Pressure Relief Valve (Schematic Symbol) - line pressure is limited to and proportional to an electronic signal

   Sequence Valve

symbol for a Sequence Valve (Schematic Symbol) - when the line pressure reaches the setting of the valve, valve opens permitting flow to the secondary port. The pilot must be externally drained to tank.

   Pressure Reducing valve

- pressure downstream of valve is limited to the setting of the valve

Flow Control Valves


   Throttle valve

symbol for a Throttle valve (Schematic Symbol) -adjustable output flow

   Flow Control valve

symbol for a Flow Control valve(variable inlet pressure) (Schematic Symbol) -with fixed output (variations in inlet pressure do not affect rate of flow)
symbol for a Flow Control valve(with fixed output and relief port to reservoir with relief for excess flow [variations in inlet pressure do not affect rate of flow] ) (Schematic Symbol) -with fixed output and relief port to reservoir with relief for excess flow (variations in inlet pressure do not affect rate of flow)
symbol for a Flow Control valve(with variable output) (Schematic Symbol) -with variable output
symbol for a Flow Control valve(fixed orifice) (Schematic Symbol) -fixed orifice
symbol for a Flow Control valve(metered flow toward right free flow to left) (Schematic Symbol) -metered flow toward right free flow to left
symbol for a Flow Control valve(pressure compensated flow control fixed output flow regardless of load) (Schematic Symbol) -pressure compensated flow control fixed output flow regardless of load
symbol for a Flow Control valve(pressure and temperature compensated) (Schematic Symbol) -pressure and temperature compensated
symbol for a Flow Control valve(variable output and relief port to reservoir) (Schematic Symbol) -with variable output and relief port to reservoir

   Flow dividing valve

symbol for a Flow divider (Schematic Symbol) -flow is divided equally to two outputs.

Shut-Off Valve

symbol for a Shut-Off Valve (Schematic Symbol) -Simplified symbol

Accumulators

symbol for an Accumulator (Schematic Symbol)

Filters, Water Traps, Lubricators and Miscellaneous Apparatus


   Filter or Strainer

symbol for a Filter or Strainer (Schematic Symbol)

   Water Trap

symbol for a Water Trap (with manual drain) (Schematic Symbol) -with manual drain
symbol for a Water Trap (with automatic drained) (Schematic Symbol) -with automatic drained

   Filter with water trap

symbol for a Filter with water trap (with manual drain) (Schematic Symbol) -with manual drain
symbol for a Filter with water trap (with automatic drained) (Schematic Symbol) -automatic drain

   Air Dryer

symbol for an Air Dryer (refrigerant, or chemical removal of water from compressed air line) (Schematic Symbol) refrigerant, or chemical removal of water from compressed air line

   Lubricator

symbol for a Lubricator (oil vapor is injected into air line) (Schematic Symbol) -oil vapor is indected into air line

   Conditioning unit

symbol for a Conditioning unit (Pneumatic Pressure Regulator) (FRL compound symbol of filter, regulator, lubricator unit) (Schematic Symbol) -compound symbol of filter, regulator, lubricator unit
symbol for a Conditioning unit (Pneumatic Pressure Regulator) (FRL compound symbol of filter, regulator, lubricator unit) (Simplified Schematic Symbol) -Simplified Symbol

Heat Exchangers


symbol for a Heat Exchanger (Schematic Symbol) -air or water cooled unit designed to remove heat from oil returning to reservoir