Why 3 lines for the backhoe attachment?

[BuggyMasters]

I’m installing the backhoe on my 2538. Why three lines? I believe one is a relief line going back to the tank but why is this needed? If this is an open center system with everything in series, seems there is already a relief line at the loader valve. So why that 3rd line?

 

[mikester]

On my M59 3 lines are as follows
1.Main Hydraulic Pump
2.Swing Hyd. Pump
3.Tank Port

Allows more than one function at a time, prevents Peter from robbing Paul

 

[K5lwq]

One hose feeds the backhoe. One hose is the return to tank. And the third hose is power beyond that feeds 3pt and remote valves.

When you have the backhoe disconnected you need to loop the power hose to the third hose.

 

[workinonit]

3 limes? Maybe the backhoe likes his margaritas more citrusy.

 

[ROUSTABOUT]

Well, if it's open center, where will the fluid go when you're not using the valve?

 

[BuggyMasters]

I gotta get my head wrapped around this. Consider the standard loader valve. You have 1 that feeds it with “supply” pressure, 4 that go to loader functions, one power beyond, and one back to tank, right? The power beyond is simply a “pass through” supply pressure line, right? If that’s a correct then maybe my confusion is in my 3rd function valve. It only has 4 lines. Power beyond from the loader valve (thus its supply pressure), a power beyond out (which is supplying pass through supply pressure to downstream things like 3 point hitch), and then two lines that operate the cylinder for my grapple. Why doesn’t this 3rd function have another line for relief? Why does that backhoe….well actually I guess that’s just like the 3rd function…has 4.I gotta put this on paper to make it work in my head.

Its correct to think of the power beyond as a “pass through” supply line, correct?

 

[workinonit]

I'm with you. It makes no sense to me. Usually all the "magic" is done at the diverter valve or the 3rd function valve if the hydraulics are live. I would see no reason to have a PB line going out to the 3rd function or a return line from the 3rd function. But all that said I'm a hydraulics idiot. Just when I think I understand something I find that I don't.

 

[K5lwq]

The 3rd function valve is designed to handle the back pressure from down stream valves so that is why it does not need a separate tank port. Power beyond will go from loader valve to 3rd function valve then to the backhoe power in port.

The backhoe valve has a tank port only and not power beyond because they do not want you using the 3pt or remotes with the backhoe attached.

When you detach the backhoe then you will need to take the power line and plug it to the 3rd hose so it can complete the circuit and feed the 3pt and remote valves again.

With these two hoses connected and backhoe removed it is as you explained. Power beyond feeds 3rd function then goes back through the loop to feed 3pt and remote valves.

 

[BuggyMasters]

Well I went to my Mahindra store and lo-and-behold…they changed the loader valve again on the 2638! Couldn’t believe it. On the 2638 I have in my building right now, there are two lines that come off the right side of the tranny. On my setup these hard lines go to an intermediate plate and on the backside of that plate are the hoses that go to the loader valve. On the new ones, they got rid of that intermediate plate. Those hard lines go directly into the loader valve. So that really peed on my parade. What I am doing is taking a backhoe off of a 2638 and putting it onto a 2538. So I need to return the 2638 back to stock. My goal was to see what lines go where in stock form but no go on that now because the newest 2638 does not have this intermediate plate.

Also, all indications are that the 2638 does not have a dedicaged power beyond port. Instead, they T off of the supply line. On my 2638 they T off right where it goes on the loader valve. On the newest 2638, they T off where the supply line comes out of the tranny. On my 2538 I have a dedicate power beyond port. Still wrapping my head around this.

 

[BuggyMasters]

Here is a picture of the latest greatest valve. The lines coming from tranny area go directly into this valve assembly.