Hydraulic drive for small tractor 3

[fluidlearning]

Hi. I need to transfer 12 Hp from a gas engine to a differential transmission, it is too difficult to do it by mechanical means, and so I chose hydraulic drive. I have a gear pump that will couple to the engine, and would like to use a gear pump as a motor to drive the transaxle input. It looks like the transaxle input will be around 1500 RPM. Can I use a gear pump as a motor? I got the hydraulic parts off Ebay and don’t have the specifications, so I will have to wing it. Any suggestions would be appreciated.

 

[fluidlearning]

The engine was at idle, 300 PSI was observed when the enging PRM's increased. If the motor was turning, the pressure was around 50 PSI.
I think you are correct, by the way the motor was acting the pressure must have been equal on both sides of the gear, so that it would not start, and when I gave it a push the flow started but when it became loaded, the pressure equalizes around the gears and it stalled.
I found instructions on the web to reverse the motor (when it was a pump) maybe this will direct the flow without causing the problem of binding up the gear set.
I am hunting for a 'real' motor to complete this project. Thanks

 

[kcj]

Its not that pressure equlaizes around the gears (unless the motor is really bad and worn) its that the shaft seal/side plate cavity is ported to the suction port when used as a pump. If that drain port sees high pressure either from inlet when used as a motor, or high tank line pressure due to valve restriction, then it pressurizes side plates and squeezes in on the gear set.

Also, same comments. If no RV, then there is a reason the pressure only builds to 300 psi when pump is turning but motor is not. Something is seriously worn.

 

[fluidlearning]

I have a spool valve in series with the pump output to the motor, it is intended to operate a cylinder that I have not hooked up yet.

I ran a test and with the motor stalled, quite a bit of fluid did flow through it. I cannot see how it can get that much flow past the gears and wearplates, I dissambled it and do not see anyway it can pass that much flow.
So, I'll keep looking for a motor.

Meanwhile can I test the system by putting a loop on the spool valve cylinder ports (it does have an RV), and take the output (power beyound) back to the tank, bypassing the motor? Then can I operate the valve which will go through a blocked state and expect to see higher pressures, until the RV operates? This will test the pump and also check what the RV is set at.

Thanks for your patience.

 

[kcj]

1. Was this motor by chance a vane type pump used as smotor? I assumed gear type, but maybe. . . . Vane pumps do not have springs to push the vanes outward, they depend on centrifugal force. As the pump they are turning. as a otor, they are not, no force, vanes stayinward, leaks totally by.

I don't follow your second valve description. To check RV settings, just shift the spool against the plugged port and force all pump flow across the RV.

However, the RV should be first in line next to the pump, not after the motor. Caution: full pressure applied to both ports of themotor may or may not daucse damage, depending on motor ratings. It puts twice the thrust loads on bearings etc.

The RV in the spool valve should be set lower than manin RV, if you with the cylinder circuit limited at a lower pressure

 

[fluidlearning]

I have a 'real' motor coming, but the pump I was trying to use as a motor was a gear pump.

Let me see if in underatand the function of the RV (standalone) I used one on the first backhoe I built. It basically was a spring valve that would open when it reached the pressure setting and bybass the output of the pump back to the inlet. It was inserted into a tee in the pump outlet that fed the cylinder valves.

Aside from the motor functions.
The spool valve I am using has an inlet and outlet port and two smaller ports for the cylinder that I am going to control, it has an adjustment on the side that I assume is an RV and will bypass any excess pressure through the valve and out the outlet port. (Maybe I should put an RV at the pump outlet).

The motor should be in about two weeks. I will post pictures of the tractor and hydraulic systems to my web page later this week so you can see what I am talking about. Don't laugh, I have to make do with what I have, this is a hobby for me

 

[kcj]

RV valve your udne4standing is correct. Limits the pressure, although bypasses back to tank, not to pump inlet.

Need an RV at the pump, or inlet to motor valve, or anywhere ahead of the first load. If the motor stalls, the oil never reaches the RV in the second valve for the cylinders.

kcj