Hydraulic motors

[chvet73]

I am attempting to build a 3pt to "Quick-Tach" converter for my old 722 Bobcat. There are several on the market. A few of them are 'powered' for a PTO. My knowledge of hydraulic motors is hurting my efforts. I need help in knowing what motor to select. acccording to Bobcat the pump puts out 10 GPM at 2100psi.
The question is what motor to choose to give the appropriate RPM, power and shaft size to make a PTO.
Thanks for any help in advance.

 

[Villengineer]

RPM=(231*GPM)/Displacement of motor in^3/revolution
Since you want 540 and if you have 10 GPM then you need a 4.28 in^3/rev. motor displacement.
Your max torque at 2100 psi for this motor will be 1430 inch pounds which result in roughly 12.25 HP.
I'm having touble remembering the exact shaft, but 1-3/8" x 6 spline seems to stick out in my mind. Somebody will correct me if I'm wrong.

 

[IH_4_Me]

</font><font color="blue" class="small">( I'm having touble remembering the exact shaft, but 1-3/8" x 6 spline seems to stick out in my mind. Somebody will correct me if I'm wrong. )</font>
Yep thats the correct size for your standard tractor pto. I've been doing research of late as I am in the process of designing/building a hydraulically operated rotary mower and needed shaft sizes, motor power/ flow rates etc...

 

[jrlichina]

Check this out Hydraulic PTO

 

[DocHeb]

Could you give the formulas for torque and HP that you are using, and then I will add this thread to my favorites for hydraulics!

 

[Villengineer]

Hydraulic motor formulas:

Torque=(PSI*Displacement (in^3/rev))/(2*pi)

HP=(Torque (in lbs)*RPM)/63025

Remember that these will give you the values as if there are no losses. Actual values most likely will be lower. Hope you find this helpfull.

 

[chvet73]

First, thanks for the info so far. I was looking at the link to the Hydraulic pumps. Can these pumps function the same as a Hydraulic motor?

 

[Villengineer]

In general pumps should not be used as motors. There are some that can be used like this, but for most pumps it's not advisable. The internal design and seal systems on pumps usually aren't designed to accept high pressure from both the inlet and outlet, while motors commonly are. I see two problems with the pumps in that link. First, they have a female connection to be mounted on a PTO, not provide PTO. YOu would have to get a shaft made and figure out a way to retain it. Second, and just as important, as a Buckeye I can not condone the support of the school up north in any manner. Just kidding, of course.

 

[chvet73]

That kind of what I figured on pumps. As an Ohio State grad, long removed from Ohio, I appreciate that input. Anyone have any examples of what motor might work. THANKS

 

[DocHeb]

I think what you want is a SkidSteerAttachments EZ-PTO Drive.

The pump on this unit doesn't seem like anything special. Using 10 gpm @ 2100 psi, an appropriate pump could be a Prince Hydraulic Pump, such as the AEM. Looking at page 117 of the "pumps"
catalog, an AEM 75 would have 4.6 cubic inch displacement, withstand 1700-2400 psi, and have a maximum speed of 800.

The hard part will be the adapter from the pump to the PTO drive (male 1 3/8" 6 spline.) The Prince pumps come with 1" keyway, splined, tapered, or crosshole shafts. I've seen 1" keyway to female PTO 1 3/8" 6 splines, but that won't help much. You might be talking to a custom machining shop for this.