Industrial Electrical and Maintenance
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Fluid Symbols

Basic Symbols

   Line

Continuous line (flow line)
Long dashes (flow line)
Short dashes (flow line)
Double mechanical connections(shafts,levers,piston-rods)
Long chain thin Enclosure for several components assembled in one unit.

   Circle,semi-circle

Circle As a rule, energy conversion units(pump, compressor, motor)
Circle Measuring instruments
Circle Non-return link, roller etc.
Circle Mechanical link, roller etc.
Circle Semi-rotary actuator

   Square, Rectangle

Squares As a rule, control valves (valve) except for non-return valves.

   Diamond

Diamond Conditioning apparatus(filter, separator, lubricator, heat exchanger)

   Miscellaneous Symbols

Flow line connection
Spring
Restriction (affected by viscosity)
Restriction (unaffected by viscosity)

Functional Symbols

   Triangle

Solid Direction of Hydraulic Fluid
In outline only Direction of Pnematic flow or exhaust to atmosphere

   Arrow

Line Indication of direction
Curve Indication of rotation
Other lines -path and direction of flow through valves(as a general rule the line perpendicular to the head of the arrow indicates
that when the arrow moves, the interior pathe always remains connected to the corresponding exterior path.)
Sloping arrow -indication of the possibility of the regulation or a progressive(proportional)variability.

Pumps and Compressors

(convert mechanical energy into hydraulic or pneumatic energy.)

   Fixed Capacity hydraulic pump

  One direction of flow
  Two directions of flow

   Variable displacement hydraulic pump

  One direction of flow (uses sloping arrow symbol)
  Two directions of flow (uses sloping arrow symbol)

   Fixed capacity compressor

  Always one direction of flow

Motors

(convert hydraulic or pneumatic energy into rotary mechanical energy.)

   Fixed Capacity hydraulic motor

  One direction of flow
  Two directions of flow

   Variable displacement hydraulic motor

  One direction of flow (uses sloping arrow symbol)
  Two directions of flow (uses sloping arrow symbol)

   Fixed displacement pneumatic motor

  One direction of flow
  Two directions of flow

   Variable displacement pneumatic motor

  One direction of flow (uses sloping arrow symbol)
  Two directions of flow (uses sloping arrow symbol)

   Oscillating motor

  Hydraulic
  Pneumatic

Pump/Motor Units

(unit with two functions,either as a pump or as a rotary motor.)

   Fixed displacement pump/motor unit

Reversal of direction of flow functions as pump or motor according to direction of flow
Single direction of flow functions as pump or motor without change of direction of flow
Two directions of flow functions as pump or motor with either direction of flow

   Variable displacement pump/motor unit

Reversal of direction of flow (uses sloping arrow symbol)
Single direction of flow (uses sloping arrow symbol)
Two directions of flow (uses sloping arrow symbol)

Variable Speed Drive Units

Torque converter Pump and/or motor are variable capacity. (relate to remote drive)

Cylinders

(equipment to convert hydraulic or pneumatic energy into linear energy.)

   Single acting cylinder

Returned by unspecified force cylinder in which the fluid pressure always acts in one and the same direction on the extension stroke.
Returned by spring cylinder in which the fluid pressure always acts in one and the same direction on the extension stroke.(uses spring symbol)

   Double acting cylinder

Single piston rod cylinder in which the pressure fluid operates alternately in both directions(extend and retract strokes)
Double ended piston rod cylinder in which the pressure fluid operates alternately in both directions(extend and retract strokes)

   Differential cylinder

The action is dependent between the effective areas on each side of the piston.

   Cylinder with cushion

Single fixed cushonCylinder incorporating fixed cushion acting in one direction only
Double fixed cushionCylinder with fixed cushion acting in both directions
Single adjustable cushion(uses slope arrow symbol)Cylinder incorporating adjustable cushion acting in one direction only
Double adjustable cushion(uses slope arrow symbol)Cylinder incorporating adjustable cushions acting in both directions

   Telescopic cylinder

Single actingfluid pressure always acts in one direction(on extend stroke)
Double acting fluid pressure operates alternately in both directions(on extend and retract strokes)

Pressure Intensifiers

(equipment transforming a pressure x into a higher pressure y.)

One type of fluid ex.- a pneumatic pressure x is transformed into a higher pneumatic pressure y.
Two types of fluid ex.- a pneumatic pressure x is transformed into a higher hydraulic pressure y.

Air-Oil Actuator

Equal Power tranferer equipment to transform a pnuematic pressure into a equal hydraulic pressure (or vice versa).

Control Valves

   General Representation

Single square indicates a unit that controls flow or pressure (having an infinite number of possible positions that would vary the conditions of flow across one or more of its ports, ensuring the chosen pressure and/or flow depending on the operating conditions of the circuit)
Two squares indicates a directional control valve with two positions (would show flow paths through ports in actual application)
Three squares indicates a directional control valve with three positions (would show flow paths through ports in actual application)
Simplified symbol for valves in repetitionwould refer to a note on the diagram where symbol in full is shown

Directional Control Valves

Units that provide full or restricted flow by opening or closing of one or more paths(one or several squares)

   Flow Paths

One flow path
Two closed ports
Two flow paths
Two flow paths and one closed port
Two flow paths with cross connection
One flow path in a bypass position, two closed ports

   Non-throttling directional control valve

Two position would have distinct circuit conditions shown in each square
Three position would have distinct circuit conditions shown in each square
Transitory position significant position passed through while switching positions optionally shown by dashed lines

   Directional control valve 2/2

Picture from the Fluid Power Handbook & Directory: copyright Penton Manual control directional control valve with 2 ports and 2 distinct postions.
Picture from the Fluid Power Handbook & Directory: copyright Penton Controlled by pressure operating against a spring (ex. air unloading valve)directional control valve with 2 ports and 2 distinct postions.

   Directional control valve 3/2

Picture from the Fluid Power Handbook & Directory: copyright Penton Controlled by pressure in both directions directional control valve with 3 ports and 2 distinct postions.
Controlled by solenoid with spring return (showing transitory position)directional control valve with 3 ports and 2 distinct postions.

   Directional control valve 4/2

Detailed Pic- directional control valve with 4 ports and 2 distinct postions controlled by pressure in both directions by means of pilot valve (with single solenoid and spring return)
Simplified Pic- directional control valve with 4 ports and 2 distinct postions controlled by pressure in both directions by means of pilot valve (with single solenoid and spring return)

   Directional control valve 5/2

Controlled by pressure in both directions- directional control valve with 5 ports and 2 distinct postions

   Throttling directional control

Two extreme positions- unit has 2 extreme positions and an infinite number of intermediate conditions with varying degrees of throttle)
Shows the extreme positions and a central(neutral) position-
Two ports(one throttling orifice) ex. -tracer valve plunger operated against a return spring
Three ports(two throttling orifices) ex. -directional control valve controlled by pressure against a spring return
Four ports(four throttling orifices)- ex. --tracer valve plunger operated against a return spring

   Electro-hydraulic servo valve

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
Two-stage with hydraulic feedback indirect pilot operation unit which accepts an analog signal and provides a similar analog fluid power output

Non-Return valves, Shuttle valves, Rapid Exhaust valves

   Non-return valve

Free opens if the inlet pressure is higher than the outlet pressure
Spring loaded opens if the inlet pressure is greater than the outlet pressure plus the spring pressure
Pilot signal closes the valve
Pilot signal opens the valve
With restriction unit allowing free flow in one direction but restricted flow in the other

   Shuttle valve

The inlet port connected to the higher pressure is automatically connected to the outlet port while the other inlet port is closed.

   Rapid exhaust valve

When the inlet port is unloaded the outlet port is freely exhausted

Pressure Control Valves

   Pressure Control Valve

One normally closed throttling orifice (general symbol)
One normally open throttling orifice (general symbol)
Two normally closed throttling orifices (general symbol)

   Pressure Relief Valve(safety valve)

Inlet pressure is controlled by opening the exhaust port to the reservoir or to atmosphere against an opposing force (for example a spring).
With remote pilot control the pressure at the inlet port is limited to the setting of a pilot control

   Proportional Pressure Relief

Inlet pressure is limited to a value proportional to the pilot pressure

   Sequence Valve

When the inlet pressure overcomes the opposing force of the spring, the valve opens permitting flow from the outlet port

   Pressure regulator or Reducing valve

A unit which , with a pressure variable inlet pressure, gives substantially constant output pressure provided that the inlet pressure remains higher than the required outlet pressure
Without relief port
Without relief port with remote control but the outlet pressure is dependent on the pressure control
With relief port
With relief port with remote control but the outlet pressure is dependent on the pressure control

   Differential pressure regulator

The outlet pressure is reduced by a fixed amount with respect to the inlet pressure

   Proportional pressure regulator

The outlet pressure is reduced by a fixed ratio with respect to the inlet pressure

Flow Control Valves

   Throttle valve

Simplified symbol (doesn't show the control method or state of valve)
With manual control detailed(shows control method)
With mechanical control against a spring return detailed(shows control method) ex.-(braking valve)

   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
With variable output and relief port to reservoir

   Flow dividing valve

The flow is divided into two flow in a fixed ratio substanially independent or pressure variations

Shut-Off Valve

Simplified symbol

Energy Transmission and Conditioning

   Sources of Energy

Pressure source Simplified general symbol
Hydraulic pressure source Simplified general symbol (to be used when the nature of the source should be indicated)
Pneumatic pressure source Simplified general symbol (to be used when the nature of the source should be indicated)
Electric motor
Heat Engine

Flow Lines and Connections

   Flow lines and connections

Working line, return line and feed line
Pilot control line
Drain or bleed line
Flexible pipe flexible hose,usually connecting moving parts
Electric line

   Pipeline Junction

Connected

   Crossed Piplines

Not connected

   Air Bleed


   Exhaust Port

Plain with no provision for connection
Threaded for connection

   Power take-off

Plugged on equipment or lines, for energy take-off or measurement
With take-off line on equipment or lines, for energy take-off or measurement

   Quick-acting Coupling

Connected, without mechanically opened non-return valve
Connected, with mechanically opened non-return valve
Uncoupled, with open end
Uncoupled, closed by free non-return valve

   Rotary connection

One way line junction allowing angular movement in service
Three way line junction allowing angular movement in service

   Silencer

Reservoirs

   Reservoir open to atmosphere

General symbol
With inlet pipe above fluid level
With inlet pipe below fluid level
With a header line

   Pressurized reservoir

Accumulators

The fluid is maintained under pressure by a spring, weight or compressed gas (air, nitrogen, etc.)

Filters, Water Traps, Lubricators and Miscellaneous Apparatus

   Filter or Strainer

   Water Trap

With manual control drain
Automatically drained

   Filter with water trap

With manual control drain
Automatically drained

   Air Dryer

A unit drying air(for example by chemical means)

   Lubricator

Lubricates equipmentsmall quantities of oil are added to the air passing through the unit, in order to lubricate equipment receiving the air

   Conditioning unit

Detailed consisting of filter, pressure regulator gage and lubricator
Simplified consisting of filter, pressure regulator gage and lubricator

Heat Exchangers

   Temperature Controller

Maintains temperature the fluid temperature is maintained between two predetermined values. The arrows indicate that heat may be introduced or dissipated.

   Cooler

Not showing coolant flow the arrows indicate the extraction of heat
Showing coolant flow lines the arrows indicate the extraction of heat

   Heater

Arrow in diamond indicate the introduction of heat

Control Mechanisms

   Mechanical Components

Detent a device for maintaining a given postion
Locking Device (*) is the symbol for unlocking control
Over-center device prevents the mechanism for stopping in the dead center position

   Rotating Shaft

In one direction(arrows indicate direction)
In either direction(arrows indicate direction)

   Pivoting devices

Simple
With traversing lever
With fixed fulcrum

Control Methods

   Muscular control

General symbol (without showing the control type)
Controlled by pushbutton
Controlled by lever
Controlled by pedal

   Mechanical Control

Controlled by plunger or tracer
Controlled by spring
Controlled by roller
Controlled by roller(one direction only)

   Electrical Control

Controlled by Solenoid (the one winding)
Controlled by Solenoid (the two winding operating in opposite directions)
Controlled by Solenoid (the two winding operating in a variable way progressively, operating in opposite direction)
Controlled by Electric Motor

   Direct Acting Control

Controlled by application of pressure
Controlled by release of pressure
Controlled by different control areas (Larger rectangle represents the larger control area)

   Indirect Control, pilot actuated

Controlled by application of pressure
Controlled by release of pressure
Controlled by Interior control path (control paths are inside unit)

   Combined Control

Controlled by solenoid and pilot directional valve pilot directional valve is actuated by solenoid
Controlled by solenoid or pilot directional valve either may actuate the control independently
 

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