Pump types — gear, vane & piston
Every hydraulic pump traps a fixed volume and pushes it out. They differ only in how they trap it — and that one difference decides their pressure, efficiency, noise and cost.
Source: Rabie, Fluid Power Engineering, Ch. 4.
Before you start
What you need first
- Positive displacement — every hydraulic pump traps & pushes a set volume \(V_g\) each turn (Topic 19).
- Leakage & efficiency — a tighter seal means higher \(\eta_v\) (Topic 19).
What you'll be able to do
- Recognise the three main types — gear, vane, piston — and how each works.
- Explain why piston pumps reach the highest pressure.
- Match a pump type to a job by pressure, noise and cost.
Start here · the map
One family, three ways to trap oil
They are all positive-displacement pumps (Topic 19) — they differ only in the mechanism that traps the oil: meshing gears, sliding vanes, or reciprocating pistons.
Gear pumps
Two meshing gears turn in a close housing. Where the teeth un-mesh on the inlet side, a space opens and oil is sucked in; the oil is carried around the outside in the tooth gaps; where the teeth mesh again on the outlet side, the oil is squeezed out.
Gear pumps leak over the tooth tips (tip-to-housing) and at the sides (gear face to side-plate), so their efficiency is lower. They are also a little noisier, because the meshing makes the delivery slightly uneven — more teeth means smoother, quieter flow.
Good
- Cheap & simple
- Robust, tolerant of dirt
- Compact
Weak
- Lower efficiency
- Noisier, more pulsation
- Fixed displacement only
Vane pumps
A rotor carries sliding vanes inside a shaped ring (the cam ring). Spinning throws the vanes outward against the ring (centrifugal force, helped by oil pressure under the vanes), so each chamber between two vanes seals. The ring's shape makes that chamber grow (suck in) then shrink (push out) — twice per turn.
Put the two pressure zones opposite each other (an oval cam ring) and the side forces on the rotor cancel — a balanced design with low bearing load and long life. Move the ring off-centre instead and the chamber sizes change, which is how a vane pump becomes variable displacement.
Good
- Quiet, smooth flow
- Good at medium pressure
- Can be made variable
Weak
- More parts than a gear pump
- Sensitive to dirt
- Not for the very highest pressures
Piston pumps — the high-pressure champions
Several pistons reciprocate in a block. A round piston in a round bore seals very tightly, so very little oil leaks back even at huge pressures — which is why piston pumps reach the highest pressure with the best efficiency.
In an axial swash-plate pump the pistons sit in a rotating block and ride on a tilted plate; the tilt strokes them in and out. In a bent-axis pump the block is set at an angle to the shaft, and the angle does the same job. Change that angle and you change the stroke — so the displacement changes while the pump runs. This is how piston pumps become variable (Topic 22). Radial piston pumps point the pistons outward from the centre and reach even higher pressures, but are larger and heavier.
Good
- Highest pressure
- Best efficiency
- Easily variable displacement
Weak
- Most expensive
- Complex, many parts
- Needs clean oil
The three types at a glance
| Type | Pressure | Efficiency | Noise | Cost |
|---|---|---|---|---|
| Gear | Low–medium | Fair | Higher | Lowest |
| Vane | Medium | Good | Low | Medium |
| Piston | Highest | Best | Medium | Highest |
✏️ Try it yourself — no numbers needed
- In an external gear pump, oil is drawn in where the teeth do what?
- What throws a vane pump's vanes out against the cam ring?
- Why does a piston pump reach the highest pressure?
Recap — the whole topic on one screen
| Type | How it traps oil | Best at |
|---|---|---|
| Gear | meshing gears carry oil around | cheap, robust, dirt-tolerant |
| Vane | sliding vanes in a cam ring | quiet, medium pressure, can be variable |
| Piston | pistons stroked by a swash plate / bent axis | highest pressure & efficiency, easily variable |