Hydraulics & Fluid Power Reference Library · Wall Charts

Hydraulic Symbols Chart

Plain-language descriptions of the most common ISO 1219-1 fluid power symbols for pumps, motors, valves, cylinders and lines, and how to read a valve envelope.

Ref HY-0050ISO 1219-1

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Hydraulic schematics use graphic symbols defined in ISO 1219-1 (and the older ANSI Y32.10). A symbol shows what a component does, not how it looks or where it sits on the machine. Reading the symbols lets you trace flow from pump to actuator and back to tank.

How to read it

Lines: a solid line is a working (pressure, return or suction) line. A dashed line is a pilot or drain line.
Triangles: a solid triangle means hydraulic. A hollow triangle means pneumatic. The point shows flow direction.
Arrows across a symbol mean the component is adjustable or variable.
Valve envelopes: each square is one valve position. Arrows inside show flow paths. A T-shaped mark means a blocked port.
The valve is drawn with lines connected to the square that shows its normal (unactuated) position.
Actuators (solenoid, lever, spring, pilot) are drawn on the ends of the valve.

Symbol chart

Symbol (as drawn)	Meaning
Circle with a solid triangle pointing outward	Hydraulic pump (one triangle = one flow direction)
Circle with a solid triangle pointing inward	Hydraulic motor
Pump or motor circle with a diagonal arrow through it	Variable displacement
Open-top rectangle	Reservoir (tank)
Diamond with a dashed line across it	Filter or strainer
Diamond with a solid line and triangles	Cooler or heater (see legend)
Ball in a V-shaped seat	Check valve
Single square with offset arrow, spring and dashed pilot line	Pressure relief valve
Two or three squares side by side	Directional control valve (2- or 3-position)
Rectangle with a piston line and rod	Double-acting cylinder
Oval or capsule shape	Accumulator
Circle with a needle	Pressure gauge
Two curved lines pinching a flow line	Flow control (restriction)
Dot where lines meet	Lines joined
Box drawn with a dash-dot line	Several parts in one assembly or manifold

Key points

Port letters are usually P (pressure), T (tank), A and B (work ports) and L or Y (drain), X (pilot).
A closed-center, tandem or open-center valve is shown by the paths in the center square.
Check the drawing's legend and the machine's parts list. Makers add their own symbols.

Common mistakes

Reading the drawing as a physical layout.
Confusing a drain line (dashed) with a pressure line.
Missing a check valve in a line, which changes which way flow can go.

Governing standards: ISO 1219-1 (graphic symbols); ISO 1219-2 (circuit diagrams); machine manufacturer schematics.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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