pto pump to a mahindra 3710 backhoe

[Billself]

So I bought this used Mahindra 3710 backhoe off a friend of mine and now I am stuck. I bought the smallest pto pump i could find which is 7gpm then i bought a 10gal. tank to feed it , got it all hooked up and now its shutting the tractor down when i start the pto . I capped the PB off sense i don't need it and used a 3/4 suction hose on inlet side of pump and went down to the hoses that came with the backhoe. small dont know what size,prob. 3/8 or 1/4 not sure.Problem is every time i let the clutch out on tractor it stalls it, if i slip the clutch it pumps but at a real strain i have checked the hoses for junk in the lines but clean, then i uncapped power beyond and ran to a bucket it works fine that way, just cant use the hoe know pressure to run it. the only thing i can think of is its too big of a pump. i ran the tractor at diff. rpm to try to force the fluid trough but to much strain,is it possible to run a smaller inlet hose from 3/4 to 1/2 to keep some fluid away from pump side thinking its just to much fluid trying to pass through mahindra controller. I'm just stuck dont know what to do and i need this backhoe as soon as possible. Please any help would be great i really gotta get this going thanks again. PS. pto is at 540 rpm

 

[Billself]

gonna use a hydraulic 1/2 hose to try and feed the pump on suction side see if that will cut down the fluid to controllers enough to where it wont cause a stall on tractor and still give it enough fluid to run the hoe. What do you guys think??

 

[Billself]

also if I increase the pressure relief valve will it allow more fluid to pass through the controller, it seems to be slowing the fluid in there somewhere just dont understand where

 

[100 td]

.......I capped the PB off sense i don't need it............ it seems to be slowing the fluid in there somewhere just dont understand where

If you capped the PB then you are dead heading the pump, or putting it into constant relief, depending on your valve.
Flow (constant) has to go in and out, the valve was set up to go out the PB line to the next valve and return to tank. So either the valve needs to be modified so it has no PB or the PB line needs to return to tank.

 

[100 td]

You pump isn't too big, don't fit smaller hoses.

 

[100 td]

And one other thing, check your valve has a built in relief on the inlet side, as when fitted to a Mahrindra tractor running off tractor hydraulic, it may use the tractor relief to protect the pump. If you don't have a relief, you will blow your pump or hoses when you hold a valve at end of stroke.
Edit: System relief needs to be set at 2050 psi or lower.

 

[100 td]

Your tractors hydraulic pump is likely big enough to run this backhoe from the specs i can find, however, there may be a priority flow controller on the pump that sends some of the flow to the steering controller. I don't have the hydraulic circuit of this machine so can't comment on what flow goes where, but if all flow was channeled to the 3pt/pressure line when no steering was used, there would be enough flow. However, operating with PTO pump may be easier, no idea of PTO hp from your machine, nor have I done calcs to see what you require.

 

[rScotty]

I'm going to guess that the problem is in the PB (power beyond) cap. PB is a mess. Depending on the brand and model of the spool valve bank (sometimes called the control valve bank), the PB port may be able to be simply capped off as you did with a pipe plug.....or it may require a special long plug that also internally routes the PB flow back into the return port inside the control valve body. And from there the entire flow goes to the tank. Which way your PB works just depends on the make and model of your particular control valve. Sometimes you can figure what type yours is by looking up the make and model of the control valve online and looking at the parts list. Check if the picture of the PB blocking cap looks like a simple pipe plug or if it looks like a more complex fitting.

A quick and dirty way to check this on the tractor right now would be to simply unblock the PB port and plumb the PB port to flow into the return line to the tank. If that takes the load off of the system, check with the control valve manufacturer to see if you can use it that way or if it needs the special PB fitting.

Normally a return line from the controller to the tank is several sizes larger than the pressure line from the pump to the controller. From the tank to the inlet side of the pump you use the same size hose as the return line and position it so that it flows freely into the pump without bends that would trap a large air bubble.

DO NOT go down on the size of the pressure line going from the pump to the control valve. That won't help. Stay at least as large or even go to the next size larger than the size of the lines going from the spool valve controller to the cylinders.
luck,
rScotty

 

[N2DFire]

I am no hydraulic expert by any means but from my limited knowledge & experience this should be pretty simple, and I'm in agreement with the others that you're somehow deadheading / locking the pump and that's why your tractor is stalling.

Assuming no one has tampered, changed, altered, or added anything to the BH it should have 2 hoses coming off of it - 1 pressure in and 1 return line and the PTO pump should have one inlet port & one (or two) outlet ports

Pump out goes to BH pressure line, BH return line goes to tank, and tank goes to pump inlet.


I'm confused as to what you capped off and why when you say you capped off the PB port. The port on what? Why was it uncapped to begin with?
Also how is fluid getting from the BH back to the tank, where is that connection on the manifold?


rScotty has given you some great troubleshooting advice and I think this is spot on as well.

If you capped the PB then you are dead heading the pump, or putting it into constant relief, depending on your valve.
Flow (constant) has to go in and out, the valve was set up to go out the PB line to the next valve and return to tank. So either the valve needs to be modified so it has no PB or the PB line needs to return to tank.

If you can post pictures of the pump & the control valves - esp any markings that indicate in, out, tank, PB, etc and describe how you have things connected, I'm sure we could pick up on the issue much quicker.

 

[Billself]

well i ordered a pressure releif valve to put on pto pump its self so i can run another hose to return line along with the hose off of controller. took a look at the relief valve on backhoe today when i came home and it looks to me that the relief valve goes before controller and pops off into the power beyond not sure sense it looked like someone has monkeyed with it not sure what they did but when i took it apart top part of valve was screwed all the way out then as i took the top part out they put a washer under main bigger spring on the bottom but cant understand why seems like they tried to keep bottom spring tight and the other loose cant figure that one out but prob. screwed up the tension of the springs dont know how to set them without pressure gauge attached to a line so when the new valve arrives i ll try to make sense of it or just do away with that valve somehow sense its bolted to controller dont know if i can but at least i'm trying to head in the right direction but boy time is not on my side.