What happens to a hydraulic pump when running at a lower RPM than reccomened?

[MacandTosh]

Does anybody know what happens to a pressure compensated piston pump in the regime of 0 RPM and minimum RPM, aside from heating issues or inefficiencies?

Specifically:

If I want to accelerate the RPM of the pump from 0 to say 1800 RPM (the max RPM of the pump), that means I will have to pass the regime of 0 to, say 500RPM (500 RPM is minimum recommended RPM). If I set the max system pressure to 2000 PSI, what will happen to the pressure (and in this case the torque to the motors) when I'm passing through that regime?

The pressure is most likely going to spike up after a rotation or two since the fluid is not easily compressible but will go back down and up I'd imagine.

I'm anticipating that when my pump's RPM is lower than 500 RPM and my vehicle is moving forward, the motors will be slowing down my acceleration since my motors will effectively be pumps.

But will this severely damage the pump? I don't plan to run it in this regime that often.

 

[90cummins]

Does anybody know what happens to a pressure compensated piston pump in the regime of 0 RPM and minimum RPM, aside from heating issues or inefficiencies?

Specifically:

If I want to accelerate the RPM of the pump from 0 to say 1800 RPM (the max RPM of the pump), that means I will have to pass the regime of 0 to, say 500RPM (500 RPM is minimum recommended RPM). If I set the max system pressure to 2000 PSI, what will happen to the pressure (and in this case the torque to the motors) when I'm passing through that regime?

The pressure is most likely going to spike up after a rotation or two since the fluid is not easily compressible but will go back down and up I'd imagine.

I'm anticipating that when my pump's RPM is lower than 500 RPM and my vehicle is moving forward, the motors will be slowing down my acceleration since my motors will effectively be pumps.

But will this severely damage the pump? I don't plan to run it in this regime that often.

Piston pumps (hydrostatic transmissions) do not like slow speeds assuming you are referring to the engine driven pump in the system.
These units typically have a separate charge pump and the supply is dependent on adequate input rpm to properly charge the hydrostatic system with adequate pressure and flow.
These systems will typically talk to you (growl) at speeds that are too slow to properly charge the system.
Simple gear or gerotor pumps are unaffected by slow speeds but can cavitate at excessively high speeds when the oil cannot flow to the pump fast enough.
Cavitation can damage pumps over time.

Hope this helps!!

90cummins

 

[MacandTosh]

Thanks!

I have eyed a gear pump for that very reason, but that would require me to use an open-loop system for my application, and that's a lot of weight I don't want to haul around if I can avoid it.

So it sounds like cavitation could be the leading side effect of this? Normally what might the lifespan of a pump cavitating look like? I don't need crazy high operating hours, I'm expecting maybe 50 hours of operation for this application at most. Anything beyond that would be nice for the future, but not necessary.

 

[oldnslo]

Macandtosh
Can you explain your application in a little more detail?
I agree with 90cummins on pumps don稚 like low RPM but depending on how they are being applied you may be able to do some things to make them work better at low RPM

Some Examples if closed loop Hydrostatic

Use oversized charge pump help keep system full at low RPM
Make sure reservoir is mounted higher and as close as possible to pump to prevent cavitation at low RPM

 

[MacandTosh]

I'm just trying to learn more about hydraulics in my spare time, and I thought it'd be a nice challenge to build a hydraulic transmission for a go cart.

 

[90cummins]

I'm just trying to learn more about hydraulics in my spare time, and I thought it'd be a nice challenge to build a hydraulic transmission for a go cart.

In that application the load would likely be on the low side. If you have the system on hand or can obtain it cheap enough go for it. We could all learn a thing or two here.

90cummins