Hydraulic motor for fence trimmer

[krm944]

My winter/spring project is to make a fence line trimmer that I can mount on the pallet forks. I have auxiliary hydraulic ports on the Case DX35 so I would like to power the trimmer by hydraulics.

Total hydraulic flow is 14.9 gpm, 5 gpm to steering and 9 pump.

I’m looking for an inexpensive used hydraulic motor to use, but I don’t know how to size one up.

A Case\Ingersoll Mower drive unit is available locally for the right price. Would it work?

 

[MossRoad]

You have to decide how fast you want the motor to be turning first.
RPM

Then you have to know how many GPM of flow you have.
GPM

And what PSI is available, too.
PSI

Then you can plug in the numbers into hydraulic calculators to determine how many cubic inches of displacement your hydraulic motor needs to be to give you the RPMs that you want at the GPM you will be providing and the PSI it can develop.

Here's a link to some calculators at Surplus center for a start.

Surplus Center

 

[agjones]

For reference the dr power 3pt string trimmer uses pulleys to up the tractor pto rpms from 540 to ~2200 for its 22" string head. They achieve the same rpm range by stepping down rpms of a 7.25 engine from 3600 max.

Most modern tractors are in the 2100-2500 psi range.

4 gpm through a hydraulic motor with 0.42 displacement gets you in the right range. At 8 gpm you'd need a displacement of 0.84...

Those case/ingersoll tractors put 8.5-9.5 gpm to the attachment (tiller, mower, blower). So if you know your aux circuit is putting 9gpm out, then yes that motor should be a pretty good match. The case components were rated to 3000psi, even though their tractor was lower.

If needed you can include a flow control valve in the setup to send excess flow back to the tank. One thing to consider is that your aux may be intended to power actuators rather than hydraulic motors... If it's a really long fence or hot day... Just be sure your tractor is capable of maintaining the temperature of the hydraulic fluid. Aux plumbing just for a loader may not include any oil cooler...