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
	Manual control directional control valve with 2 ports and 2 distinct postions.
	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
	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)