Understanding Hydraulic & Pneumatic Symbols

Table 1 Basic Symbols, Pipelines, and Connections (GB/T 786.1—2009)

Name	Symbol
Oil Supply and Return Lines
Control Lines, Drain Lines, Flushing Lines, and Vent Lines
Combination Component Outline
Connection of Two Fluid Lines
Connecting Line
Crossing Line
Hose Assembly
Interface
Control Line or Drain Line Interface
Closed Line or Interface
Rotary Joint
Three-Way Plug Valve
Three-Way Rotary Joint
Quick-Disconnect Coupling without Check Valve, Disconnected State
Quick-Disconnect Coupling with Check Valve, Disconnected State
Quick-Disconnect Coupling with Two Check Valves, Disconnected State

Table 2 Control Structures and Control Methods

Name	Symbol
Control Mechanism with Separate Handle and Positioning Pin
Push Rod with Adjustable Stroke Limiter
Push or Pull Control Mechanism with Positioning Device
Manual Locking Control Mechanism
Control Mechanism with 5 Locking Positions
Roller Lever for Single Stroke Direction Operation
Control Mechanism with Stepper Motor
Single-acting solenoid, action towards the valve core
Single-acting solenoid, action away from the valve core
Double-acting electrical control mechanism, action towards or away from the valve core
Electrically operated pneumatic pilot control mechanism
Electrically operated hydraulic pilot control mechanism with external oil supply
Mechanical feedback
Pneumatic reset, pressure supplied from the valve inlet
Pneumatic reset, external pressure source
Double-acting electrical control mechanism, action towards or away from the valve core, continuous control

Table 3 Pumps, Motors, and Cylinders

Name	Symbol
Variable pump
Bidirectional flow, variable pump with external leakage oil path and unidirectional rotation
Fixed displacement pump or motor with unidirectional rotation
Joystick control, pump with restricted disc angle
Swing actuator or rotary drive with restricted swing angle, bidirectional flow
Single-acting single-rod cylinder, return stroke by spring force
Double-acting single-rod cylinder
Single-acting cylinder, plunger cylinder
Double-acting band-type rodless cylinder, with end cushioning on both ends of the piston
Double-acting double-rod cylinder, different piston rod diameters, cushioning on both sides, adjustable on the right side
Single-acting clamp with permanent magnet piston
Motor
Air compressor
Vacuum pump
Bidirectional swing motor with fixed flow rate and direction change
Single-acting semi-rotary cylinder or swing motor
Single-acting telescopic cylinder
Double-acting telescopic cylinder
Double-acting cylinder with end-of-stroke positioning
Electro-hydraulic servo-controlled variable hydraulic pump
Variable pump with constant power control
Continuous booster, converts gas pressure p 1 to liquid pressure p 2

Table 4 Control elements

Name	Symbol
Two-way two-position directional control valve, two-way two-position, push control mechanism, spring return, normally closed
Two-way two-position directional control valve, two-way two-position, solenoid operated, spring return, normally open
Two-way four-position directional control valve, solenoid operated, spring return
Two-way three-position directional control valve, solenoid operated, spring return, normally closed
Relief valve, direct-acting, opening pressure adjusted by spring
Sequence valve, manually adjustable setpoint
Sequence valve with bypass valve
Two-way pressure reducing valve, pilot-operated, external drain type
Three-way pressure reducing valve (hydraulic)
Adjustable flow control valve
Adjustable flow control valve, unidirectional free flow
Flow divider, splits input flow into two output streams
Check valve, allows free flow in one direction only
Double check valve, pilot-operated
Shuttle valve (“OR” logic), automatically connects the higher pressure inlet to the outlet
Proportional relief valve, direct-acting, controls hydraulic solenoid directional seat valve by adjusting spring length via solenoid
Proportional flow control valve, direct-acting
Proportional directional control valve, direct control
Pressure and directional control cartridge valve insert, valve seat structure area 1:1
Pressure and directional control cartridge valve insert, normally open, valve seat structure, area 1:1
Proportional relief valve, pilot control, with solenoid position feedback
Externally controlled sequence valve
Internally reversible pressure regulating valve
Pressure reducing valve, remote pilot, adjustable, forward flow only
Quick exhaust valve
Double pressure valve (“AND” logic), and only when both inlets have pressure will a weaker signal be output from the outlet

Table 5 Auxiliary components

Name	Symbol
Filter
Tank breather filter
Filter with auxiliary magnetic core
Filter with optical blockage indicator
Cooler without coolant flow indicator
Liquid-cooled cooler
Heater
Temperature regulator
Tachometer
Air source treatment device, including manual drain filter, manually adjustable overflow pressure reducing valve, pressure gauge, and oil mist separator. (The above is a detailed schematic, the below is a simplified diagram)
Oil mist separator
Air dryer
Oil mist lubricator
Single-acting pressure medium converter, converts gas pressure to equivalent liquid pressure, and vice versa
Diaphragm type gas accumulator
Piston type gas accumulator
Gas cylinder
Pressure gauge
Differential pressure gauge
Thermometer
Liquid level indicator
Flow indicator
Flow meter
Lubrication point
Vacuum separator
Manual drainage fluid separator
Vacuum generator
Air tank