BCIT: Millwright Level 3 (Hydraulic + Pneumatic Systems: Key Components & Symbols)

Supply line

Main line carrying pressurized fluid to components.

Return line

Line that carries fluid back to the reservoir or tank.

Pilot (control) line

Small control line used to actuate or control valves.

Drain line

Line used to remove leakage fluid from components.

Electrical control line

Line indicating an electrical control signal.

Hose assembly

Flexible hydraulic or pneumatic connection.

Drain to tank

Line directing leakage oil back to the reservoir.

Return to tank

Fluid returning to tank after doing work.

Connected fluid lines

Two fluid lines connected at a junction point.

Crossing fluid lines

Two lines crossing with no connection.

Hydraulic source of energy

Device supplying pressurized hydraulic fluid (usually a pump).

Pneumatic source of energy

Device supplying compressed air (compressor).

Solenoid valve control

Electrically actuated valve using a solenoid.

Proportional solenoid valve control

Solenoid providing variable control proportional to electrical signal.

Lever valve control

Manual valve control using a lever.

Pedal valve control

Valve controlled by foot pedal.

Spring valve control

Spring automatically returns valve to default position.

Pneumatic spring valve control

Compressed air provides return force.

Manual override

Manual method to operate an automatic valve.

2/2 directional control valve

Valve with two ports and two positions controlling flow on/off.

3/2 directional control valve

Valve with three ports and two positions commonly used for pneumatic control.

4/2 directional control valve

Valve with four ports and two positions for double-acting cylinders.

5/2 directional control valve

Valve with five ports and two positions commonly used in pneumatics.

4/3 directional control valve

Valve with four ports and three positions allowing center flow condition.

Spring-centered directional control valve

Valve that automatically returns to the center position.

Detented directional control valve

Valve that stays in the last selected position.

Fixed displacement pump (positive)

Pump delivering a constant fluid volume per rotation.

Variable displacement pump (non-positive)

Pump where output flow can be adjusted.

Fixed displacement motor (positive)

Device converting hydraulic energy into rotary motion at a constant rate.

Variable displacement motor (non-positive)

Device converting hydraulic energy into rotary motion at a variable rate.

Air motor

Device converting compressed air into rotary motion.

Diaphragm accumulator

Accumulator using a diaphragm to separate gas and fluid.

Bladder accumulator

Accumulator using a flexible bladder to store hydraulic energy.

Piston accumulator

Accumulator using a piston to separate gas and fluid.

Direct-operated relief valve

Valve that protects system by releasing excess pressure.

Pilot-operated relief valve

Two-stage relief valve providing stable pressure control.

Sequence valve

Valve ensuring operations occur in a specific order.

Direct-operated pressure reducing valve

Valve maintaining lower pressure in part of the system.

Check valve (no spring)

One-way valve allowing free flow in one direction.

Check valve with spring

One-way valve requiring pressure to overcome the spring.

Pilot-operated check valve

Check valve that opens with pilot pressure.

Throttle valve

Adjustable restriction controlling flow rate.

Pressure-compensated flow control valve (fixed setting)

Valve maintaining constant flow despite pressure changes.

Double-acting cylinder

Cylinder powered hydraulically in both directions.

Single-acting cylinder

Cylinder powered hydraulically in one direction only.

Rodless cylinder

Linear actuator without external piston rod.

Cylinder with adjustable cushioning

Cylinder with adjustable end-of-stroke shock absorption.

Air dryer

Removes moisture from compressed air systems.

Lubricator

Adds oil mist to compressed air for lubrication.

Filter separator with manual drain

Removes contaminants and water from compressed air.

Filter separator with automatic drain

Automatically removes collected water from compressed air.