Hi all, I am an equipment builder just learning hydraulics. Thanks for being so generous with your help!
I am building a simple pipe hauler for use on a smooth concrete 3% grade and the client also wants it to be towable in free wheeling mode. I know some motors don't like this and some don't mind.
What types can handle this? Will it adversly affect the pump? With proper valving can a motor rotate in a closed loop without damage? I'd rather not add clutches, disengaging couplers.
Motor is turning ~65 rpm

not sure how complicated your machine is, but I saw a homemade self propelled cart that used a front axle from a 4wd 1/2 ton pickup. Locked the spindles straight ahead, then used a hydraulic motor driving into the differntial for propel. The unique part of the idea was that it used the lockout 4wd huybs as towing disconnects: 4wd was locked and driving. 2wd position was freewheel and towing. of course the operator had to make sure to change it each time.....

k

else, there are assorted radial piston motors that can freewheel and push the pistons in, or some that retract pistons with a pilot signal.

Thanks Kevin, I'm trying to keep within a budget. Do you know of sources for reasonable priced axial piston motors? They are pricey! Surplus Center had 1 but not 4 matched. Need it for all 4 wheels.

Correction: Radial piston motor.

For Free Wheeling Automotive Drive the use of Radial Piston Motors
is a Good Expensive Solution and mainly for medium and high torque.
I can suggest three options:
1) Use a Clutch between the driving motor(piston,gear or vane) and
...the wheel. Look at www.loganclutch.com
2) Use a Mechanical Diferential where N out=N1 + N2. It can be even
...a Planetary gearbox where you brake or Release the body.
3) Simlest and the less expennsive one , use a "Dog Clutch" as you
...can find in some 4x4 vehicles , in the Front Wheels or produce it.

You should be able to get information on standards on all Fluid power equipment (Air & Hydraulic) at the National Fluid Power association www.nfpa.com

No matter what Hydraulic Motor design you use there are fairly low RPM limits or there will be abnormally high flow at elevated RPM (4 X the RPM 4 X the Flow)that can generate a lot of heat if not plumbed correctly.

On top of that the Motors will see wear from the higher revolutions while towed and the over speeding if the towing is much distance.

My Fathers wheel Horse Garden Tractor had a Valve that had to be shifted if the tractor had to be towed. The best I remember the towing speed was less than 15 MPH and not over 30 minutes without a stop for the system to cool off.
Even the Radial Piston Motors Kevin mentiond have very low RPM Free Wheeling since the Eccentric Drive setup will cause vbration that can damage the system. You also have to bave a constant pressure source to keep the pistons away from the Eccentric.

I dont know if you are using gearboxes as your drive transmission but why not pull the centers?
Some geartrains have this ability to do it externally,by two small bolts.I really dont think the idea you have wouldnt have repercussions later.
Make up valves on the motors but I say that lightly as Bud is totally on with this one