I am making a dyno to measure go-kart engine torque for a high-school project.

I would like to use a water brake by varying input/output through a water pump and have read that this should be a positive-displacement (not centrifugal) pump.

It would be great if you could provide ideas where I could find a cheap pump. For example, could I find one at an auto wrecker? What car manufacturers would use a PD pump? Thanks for any input.

3 Answers 3


Cool project!

I know that the oil pump on my BMW is a chain-driven, positive-displacement gear-pump.

My only concern with using an oil pump is that the internals can be prone to rusting, so either you'd want to coat/plate the vanes before use or add coolant to inhibit rust formation, but the oil pump should suit your needs.

@Paulster2's suggestion of using straight engine oil is definitely a more sensible option as the oil is used to lubricate the internals.

Here are a couple of pictures that show the inside of my oil pump. The "exploded" view shows how the pump pressurizes the oil in three stages. The three gear-shaped rotors mount on the shaft at the back and act in conjunction with the ring-shaped idlers.

Top View

Oil Pump - Exploded View

  • Thanks very much Zaid. I will ask at the motorcycle wreckers.
    – user13087
    Nov 6, 2015 at 11:39
  • @Danny - I think Zaid was talking about his BMW car, not MC :-) I'm also wondering if you could use oil instead of water here ... It would provide the resistance needed, but would transfer the heat better and parts wouldn't rust. Just thinking out loud. Nov 6, 2015 at 13:18

You could probably also use an electric fuel pump to do this. A rotary vane pump is a positive displacement pump. This type of mechanical pump is used quite often in vehicles. Most can produce anywhere from 45-60psi. There are also low pressure ones which produce about 5-10psi, if you don't need the higher pressure. Using the higher pressure one, you could use a fuel (or pressure) regulator which would allow you to vary the pressure, even if you have a higher pressure fuel pump. Looking at them, you'd want one which would be "in-line" not "in-tank" ... at least I'd assume you wouldn't want an in-tank version.


A hydraulic motor/pump off industrial machinery(dumptrucks, etc...) would be another option for a PD oil pump. It would be easier to assemble too since those are designed with common mounts and fittings.

They also commonly handle pressures over 2000psi

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