2 stage pump question, will it work with a hydraulic motor ?

[jimw]

I have a hydraulic powered woods buggy with a 13 hp Honda
engine and a single stage pump. I want to change it to a
2 stage pump and be able to power my splitter as well.
What effect will the 2 stage pump have on the hydraulic
motor that powers my buggy. It is a very slow speed rig,
i am guessing it will just shift down to the lower pump
output when i put a load on it.
Pic attached of the drive train.
Thanks for any input, Jim

 

[John R]

How many GPM is the pump you have on it now, If you can match the output of the pump now, it will run the same.
Only time you'll see a difference is if it kicks into the second stage.
Second stage is usually about 1/5 or less.

 

[kevin j]

It might work fine and unload the one stage smoothly under load.

It most likely will surge badly. Unloading valves are not intended as metering valves, only as an abrupt unloading across just a couple hundred psi range. Thus, if it is moving at 11 gpm, load increases, then it unloads and is trying to supply less, say 2 gpm but motor is still turning at the rpm it was with 11 gpm. Then pressure drops, and the unloading reseats, pressure rises, etc etc.

Depending on the unloading valve, it may smoothly find a position part ways in between, but even then it would be a heat generator as flow and pressure are being throttled across that spool. Unloading valves are intended to be open or closed, not metering.

Two stage pump with high inertia loads, say a wood chipper, have same issues. Load and unload and usually unstable.