Question about hydraulic motors and cylinders

MetalChicken · Feb 23, 2005

Hi. I've just bought a 6' sweeper that currently is powered by the PTO. I was thinking about changing it so that it's driven by a hydraulic motor. My question is how do I know what size motor to get?
I've seen one on eBay that is 19cc per rev operates at 210 bar continuous 230 bar peak. Max speed 3000rpm min 500rpm.
The pump on my tractor supplies 9 gallons/min after the power steering has had its bit.

Also I have a single acting cylinder that I cannot push back in even with the hose disconnected allowing the oil to flow out freely. Is there anyhting mechanical within a cylinder that could stop it retracting?
/forums/images/graemlins/confused.gif

WhiteRock · Feb 23, 2005

First you need to determine the RPMs would like your motor to operate. If you are replacing your PTO, it may be 540. If you are changing the gear configuration it may be different.

Be sure the 9 GPM is what you have at the service port you intend to power your motor (,sounds like you have). Then use a hydraulic motor formula to compute what cubic inch displacement you need. Here is one if you need it.

You should also determine the relief pressure at the service port. This will allow you to compute your torque and hp. Your new motor should accept this pressure spec.

Oh, left out a few details... /forums/images/graemlins/smile.gif

This all assumed you have the spool valves in place for your service ports.....

Kaliburz · Mar 1, 2005

You're in luck.....

I purchased a motor a while back, and it was to replace a 540 PTO. Granted, my tractor has a GPM of 8-10. Any how, the motor I purchased maxed out at 500RPM (a really high torque monster). I was going to convert post hold auger from PTO to hydrualic drive. Still working on it. But I purchased this monster because of it's torque capacity.

Unfortunetly, the Eaton number is on the motor and I don't have it w/ me. And when I purchased this sucker a few years back, it was well over $550.00...maybe closer to $600.00 /forums/images/graemlins/blush.gif

MetalChicken · Mar 7, 2005

Hi Whiterock. Thanks for the detailed reply, sorry for taking time to get back to you.
So if I wanted to achieve 1000 rpm (which is about what the brush currently rotates at), could I simply put a 1 cubic inch motor (what would run to a max of 3000rpm) and use a flow restrictor to tune it down to 1000 rpm? Or would I need to take the torque requirements (which I am clueless about) into account....... I presume - yes!

WhiteRock · Mar 7, 2005

I do not know how much HP a sweeper requires. I recommend choosing the proper CID motor for your task. You should not use a flow restrictor in this circuit to reduce flow. This would overload your system's pressure relief valve. You could use a flow divider, but I would not recommend it. I suspect the power loss would be to high.

We also need your hydraulic service pressure or PTO HP for torque computations.

It looks like to me you need a 2 - 2.1 CID motor for 1000 RPMs. Assuming you have 2000 PSI available ( 2000 PSI @ 9 GPM gives about 12 HP) you could produce approximately 640 in/lbs of torque. With a 1 CID motor this falls off to 320. You would only have about 6.5 HP available to the 1 CID motor at 1000 RPM, using a flow divider.

Does this help?