Hydraulic Pump Symbol
Definition: The Hydraulic Pump symbol represents the component that converts mechanical shaft power into hydraulic fluid power, drawn per ISO 1219-1 as a circle with a filled (solid black) triangle whose apex points outward toward the Pressure port — the direction of energy flow into the fluid — with a Suction port drawing from the reservoir.
Also known as: fixed displacement pump, gear pump, hydraulic power unit pump, vane pump, piston pump, fluid power pump, positive displacement pump.
What the Hydraulic Pump symbol means
The Hydraulic Pump symbol denotes the energy source of every hydraulic circuit: driven by an electric motor or engine, it takes fluid in at the Suction port and delivers it at the Pressure port. The single most important convention in ISO 1219-1 fluid power symbology lives here — the filled triangle shows the direction of hydraulic energy flow. In a pump the apex points outward (from the circle centre toward the pressure port): mechanical energy is being converted into fluid energy leaving the unit. Its mirror image, the triangle pointing inward, is a hydraulic motor. Misreading this one triangle reverses your understanding of the whole circuit.
A critical conceptual point the symbol encodes: positive-displacement pumps produce flow, not pressure. Pressure is the result of resistance to that flow downstream — which is why every fixed-displacement pump symbol is almost always drawn adjacent to a relief valve teeing off the pressure line. One triangle means fixed displacement, unidirectional; two opposed triangles mean the pump can deliver in both directions; a diagonal arrow struck through the circle marks variable displacement, where the output per revolution can be adjusted (as in pressure-compensated piston pumps).
How to identify the Hydraulic Pump symbol
Look for a circle with a solid black triangle inside, apex touching the circle's rim at the outlet: that outward-pointing energy triangle is the pump signature. The Suction line typically enters from the bottom (from the reservoir symbol) and the Pressure line exits at the triangle apex. Modifiers refine the meaning: a second opposed triangle = bidirectional; a long diagonal arrow across the whole symbol = variable displacement; a small case-drain line (dashed) leaving the circle appears on piston pumps.
Hydraulic versus pneumatic is also encoded in the triangle fill: solid/filled triangles mean hydraulic (liquid), open/unfilled triangles mean pneumatic (gas) — identical geometry, different fill. There is no separate 'ANSI shape' to learn: the historical US standard ANSI Y32.10 used essentially the same circle-and-triangle forms, and modern US practice (NFPA/ANSI fluid power standards) has harmonised on ISO 1219-1, so the symbol reads the same worldwide.
Function in a circuit
Positive-displacement pumps trap discrete volumes of fluid at the suction side and carry them to the pressure side — meshing gear teeth (gear pumps), sliding vanes in a slotted rotor (vane pumps), or reciprocating pistons in a rotating barrel (piston pumps). Output flow is displacement (cm³ per revolution) times shaft speed, essentially independent of pressure apart from small internal leakage (volumetric efficiency of 85–97%). Because the pump will keep delivering flow against any resistance, a blocked outlet drives pressure up until something yields — hence the mandatory relief valve.
Suction-side behaviour matters as much as delivery: the pump must be fed at its inlet with minimal vacuum (flooded suction preferred, strainer sized generously), or dissolved air comes out of solution and vapour bubbles collapse at the pressure side — cavitation — which sounds like gravel in the pump and erodes it rapidly. Variable-displacement, pressure-compensated pumps destroke themselves as system pressure approaches the compensator setting, delivering only the flow the circuit consumes and slashing wasted heat compared with a fixed pump dumping excess over the relief valve.
Standards: IEC vs ANSI
| IEC 60617 | ISO 1219-1 defines the graphic symbol (circle, filled triangle pointing outward, plus modifiers for variable displacement and bidirectional flow) and ISO 1219-2 sets circuit-diagram drawing rules and component identification codes; port marking follows ISO 9461 (P for pressure, T for tank, common practice S for suction). IEC 60617 does not cover fluid power — electrical drawings reference the hydraulic schematic instead. |
|---|---|
| ANSI/IEEE 315 | The legacy US symbol standard ANSI Y32.10 used the same circle-and-triangle grammar; current North American practice through NFPA (National Fluid Power Association) and ANSI adopts ISO 1219-1, so modern US schematics are drawn to the ISO symbol set. Pump performance test standards include ISO 4409 and ANSI/NFPA equivalents. |
| Key difference | For hydraulic pumps there is effectively no IEC-vs-ANSI split: this is ISO 1219 territory, and the US harmonised its Y32.10 forms with ISO decades ago. The distinctions worth knowing are internal to the symbol language — filled triangle (hydraulic) vs open triangle (pneumatic), one vs two triangles (uni- vs bidirectional), and the diagonal arrow (variable displacement). |
Terminals / pins
| Pin | Name |
|---|---|
| in | Suction |
| out | Pressure |
Typical values
Displacements run from under 1 cm³/rev (micro power units) to 500+ cm³/rev (industrial piston pumps); at the typical 1,450/1,800 RPM electric-motor drive this yields flows from ~2 to 700+ L/min. Continuous pressure ratings by type: external gear pumps ~210–250 bar (3,000–3,600 psi), vane pumps ~140–175 bar, axial piston pumps 280–350 bar continuous with 420–700 bar available in high-pressure designs. Overall efficiencies: gear 80–90%, piston 88–95%. Drive power follows P(kW) ≈ flow(L/min) × pressure(bar) ÷ 600 — e.g. 40 L/min at 210 bar needs about 14 kW. Suction vacuum should stay above roughly −0.2 bar gauge; fluid is typically ISO VG 32–68 mineral oil at 30–60 °C.
Where the Hydraulic Pump symbol is used
- Hydraulic power units (HPUs) for presses, injection moulding machines, and machine tools
- Mobile equipment — excavators, loaders, tractors — driven from the engine PTO or pump drive gearbox
- Steel-mill and heavy-industry systems using pressure-compensated piston pumps for large cylinder arrays
- Log splitters and compact utility machines using two-stage (hi-lo) gear pumps
- Aircraft and marine hydraulic systems where piston pumps deliver 210–280 bar to actuators
- Hydrostatic transmissions pairing a variable-displacement pump with a hydraulic motor in a closed loop
Example
In a press circuit drawn to ISO 1219-1, the Hydraulic Pump symbol's Suction pin connects down to the reservoir through a strainer, and its Pressure pin feeds the P line toward the directional valve, with a relief valve teed off immediately after the pump and set to 230 bar. The 22 cm³/rev fixed-displacement gear pump on a 1,450 RPM motor delivers about 32 L/min; when the press cylinder stalls at the end of its stroke, flow has nowhere to go, pressure rises to the relief setting, and the excess returns to tank — exactly the fixed-pump-plus-relief pattern the outward-pointing triangle should make you look for.
Key facts
- ISO 1219-1 energy-triangle rule: a filled triangle pointing OUTWARD (toward the port) marks a pump — energy flows from the unit into the fluid; pointing inward marks a motor.
- Filled (black) triangles denote hydraulic fluid; the same symbol with open (white) triangles is a pneumatic compressor/air motor.
- One triangle = fixed displacement, one flow direction; two opposed triangles = bidirectional; a diagonal arrow through the symbol = variable displacement.
- Positive-displacement pumps create flow, not pressure — pressure results from downstream resistance, which is why a relief valve is mandatory with every fixed-displacement pump.
- Flow = displacement (cm³/rev) × speed (RPM) ÷ 1000; drive power (kW) ≈ flow (L/min) × pressure (bar) ÷ 600 at 100% efficiency.
- Typical continuous pressures: gear pumps ~210–250 bar, vane ~140–175 bar, axial piston 280–350 bar (to 700 bar in special designs).
- Cavitation — vapour bubbles collapsing from excessive suction vacuum — is the leading pump killer; keep suction lines short, generous, and flooded where possible.
- Pressure-compensated variable pumps destroke to match demand, eliminating the relief-valve heat losses of fixed pumps in idle-heavy circuits.
Frequently asked questions
How do I tell a hydraulic pump from a hydraulic motor on a schematic?
By the direction of the filled triangle. In a pump the apex points outward, toward the pressure port — mechanical energy is entering the fluid. In a motor the apex points inward — fluid energy is being taken into the unit and converted to shaft power. The circles are identical; only the triangle direction differs, per ISO 1219-1.
Why is a relief valve always drawn next to a hydraulic pump?
Because a positive-displacement pump delivers essentially the same flow no matter the resistance. If the circuit blocks (a cylinder bottoms out, a valve closes), pressure climbs until a component bursts, the pump stalls, or the prime mover trips — unless a relief valve gives the flow a path to tank at a set pressure. With fixed-displacement pumps the relief valve is a non-negotiable safety element of the circuit.
What does the filled vs unfilled triangle mean in fluid power symbols?
Fill indicates the medium: solid black triangles mean hydraulic (liquid) energy; open, unfilled triangles mean pneumatic (compressed air/gas). The geometry is otherwise identical, so a circle with an open triangle pointing outward is an air compressor, and with a filled triangle it is a hydraulic pump. ISO 1219-1 defines both.
What does the arrow through a pump symbol mean?
A long diagonal arrow struck through the circle marks variable displacement — the volume delivered per revolution can be adjusted, manually or by a compensator. A pressure-compensated variable pump reduces its stroke as pressure approaches the compensator setting, delivering only what the circuit consumes. Without the arrow, the pump is fixed displacement and any surplus flow must return to tank over a relief valve.
How much power does a hydraulic pump need?
Hydraulic output power is flow times pressure: P(kW) = Q(L/min) × p(bar) ÷ 600. Divide by overall efficiency (roughly 0.85 for gear, 0.90–0.93 for piston pumps) for the required shaft power. Example: 40 L/min at 210 bar is 14 kW hydraulic, so about 16 kW at the motor shaft — which is why that pump gets an 18.5 kW motor.
What causes hydraulic pump cavitation and how do I spot it on the schematic?
Cavitation happens when suction vacuum is excessive — undersized or clogged suction strainer, long or thin suction line, high fluid viscosity (cold oil), or a low reservoir level — causing vapour bubbles that collapse violently at the pressure side. On the schematic, scrutinise everything between the reservoir and the pump's Suction port: strainer mesh size, line size, and reservoir elevation. Audibly it is a distinctive gravel-rattle; mechanically it erodes gears, vanes, and port plates fast.
Related symbols
- Check Valve symbol
- Flow Control Valve symbol
- 3-Phase Motor symbol
- Pressure Switch symbol
- Pump (Motor-driven) symbol
- Solenoid Valve symbol
Place the Hydraulic Pump symbol on a wiring diagram or schematic in the free online circuit diagram maker — no download required.