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.
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.
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
