Schematic Symbols Chart (Design Hydraulic and Pneumatic circits)

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Basic Schematic Symbols Chart
(Hydraulic and Pneumatic circuit design)

Other fluid power informational links:

Lines

Connecting Pressure Lines (usually representing plastic tubing for pneumatic [air] lines with low pressures, metal piping for hydraulic [fluid] lines with high pressure)

-continuous line (for) flow line

-dashed line (for) pilot, drain

(Envelope) long and short dashes around two or more (Symbol/picture)

-envelope (for) 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 Pneumatic flow


Pumps and Compressors	(turn rotary torque from an AC or DC electric motor into pressure in a hydraulic or pneumatic system)

Fixed Displacement hydraulic pump
	-unidirectional
	-bidirectional
Variable displacement hydraulic pump
	-unidirectional
	-bidirectional
Compressor


Motors

Fixed displacement hydraulic motor
	-unidirectional
	-bidirectional
Variable displacement hydraulic motor
	-unidirectional
	-bidirectional
Pneumatic motor
	-unidirectional
	-bidirectional
Rotary Actuator
	- hydraulic
	- pneumatic
Cylinders

Single acting cylinder
	-returned by external force
	-returned by spring or extended by spring force
Double acting cylinders
	-single piston rod (fluid required to extend and retract)
	-double ended piston rod
Cylinders with cushions
	- single fixed cushion
	- double fixed cushion
	- single adjustable cushion
	- double adjustable cushion


Directional Control Valves

Directional control valve (2 ports / 2 positions)
	-Normally closed directional control valve with 2 ports and 2 finite positions.
	-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.
	-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
Directional control valve (4 ports / 3 positions)
	-directional control valve with 4 ports and 3 finite positions *-(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
Directional control valve (5 ports / 3 positions) Normally a pneumatic valve
	-directional control valve with 5 ports and 3 finite positions
Proportional directional control valve
Electro-hydraulic servo valve -The spool positions on these valves is variable allowing for variable flow conditions.
	-single-stage direct operation unit which accepts an analog signal and provides a similar analog fluid power output
	-two-stage with mechanical feedback indirect pilot operation unit which accepts an analog signal and provides a similar analog fluid power output


Control Methods

Manual Control
	-general symbol (without showing the control type)
	-pushbutton
	-lever
	-foot pedal
Mechanical Control
	-plunger or tracer
	-spring
	-roller
	-roller(one direction only)
Electrical Control
	-Solenoid (the one winding)
Pilot Operation
	-pneumatic
	-hydraulic
Pilot operated two-stage valve
	-Pneumatic: Sol first stage
	-Pneumatic: Air pilot second stage
	-Hydraulic: Sol first stage
	-Hydraulic: Hyd pilot second stage


Check valves, Shuttle valves, Rapid Exhaust valves

	-check valve -free flow one direction, blocked flow in other direction
	-pilot operated check valve, pilot to close
	-pilot operated check valve, pilot to open
Shuttle valve
	-to isolate one part of a system from an alternate part of circuit.
Rapid exhaust valve/Pneumatic
	-installed close to an actuator for rapid movement of the actuator.


Pressure Control Valves

Pressure Relief Valve(safety valve) normally closed
	- line pressure is limited to the setting of the valve, secondary part is directed to tank.
Proportional Pressure Relief
	- line pressure is limited to and proportional to an electronic signal
Sequence Valve
	- 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
	-adjustable output flow
Flow Control valve
	-with fixed output (variations in inlet pressure do not affect rate of flow)
	-with fixed output and relief port to reservoir with relief for excess flow (variations in inlet pressure do not affect rate of flow)
	-with variable output
	-fixed orifice
	-metered flow toward right free flow to left
	-pressure compensated flow control fixed output flow regardless of load
	-pressure and temperature compensated
	-with variable output and relief port to reservoir
Flow dividing valve
	-flow is divided equally to two outputs.


Shut-Off Valve
	-Simplified symbol


Accumulators


Reservoir (Tank)


Filters, Water Traps, Lubricators and Miscellaneous Apparatus

Filter or Strainer

Water Trap
	-with manual drain
	-with automatic drained
Filter with water trap
	-with manual drain
	-automatic drain
Air Dryer
	refrigerant, or chemical removal of water from compressed air line
Lubricator
	-oil vapor is injected into air line
Conditioning unit
	-compound symbol of filter, regulator, lubricator unit
	-Simplified Symbol