Hydraulic symbols

   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

-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 cushon

- 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 postions

   Directional control valve (4 ports / 3 positions)

-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 postions

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

-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 direct operation unit which accepts an analog signal and provides a similar analog fluid power output

-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 (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

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 indected into air line

   Conditioning unit

-compound symbol of filter, regulator, lubricator unit

-Simplified Symbol

Heat Exchangers

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-air or water cooled unit designed to remove heat from oil returning to reservoir