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.

 

[BuggyMasters]

Is what I have circled below the “return line”? In the valve picture above, the bottom-most line goes directly to this place at the back of the machine. Is this what supplies hydraulic pressure so the 3-point hitch can function? My current 2638 runs through the backhoe and then through the 3rd function valve, and then to this same place as circled below.

 

[BuggyMasters]

And lastly, here is what’s on my 2638 now. The input/supply line they have T’d off to feed the backhoe. The very bottom line is what I believe needs to go to the port at very back of tractor as circled in pic above. Very different setup to what’s on the latest 2638’s.

 

[ptsg]

Is what I have circled below the “return line”? In the valve picture above, the bottom-most line goes directly to this place at the back of the machine. Is this what supplies hydraulic pressure so the 3-point hitch can function? My current 2638 runs through the backhoe and then through the 3rd function valve, and then to this same place as circled below.

That lines comes from the Power Beyond on the loader valve and feeds that plate. Since that tractor doesn't have remotes, it then feeds the 3 pt hitch. That plate also has a relief valve.

 

[BuggyMasters]

So it is the last in line on the series then, correct? Aka the return.

 

[BuggyMasters]

And on the new loader valves, this is the power beyond?

 

[newbury]

Who changed the title from "limes" to "lines"?

 

[BuggyMasters]

Ha ha…I did. Fat fingers…

 

[Bentrim]

Maybe if the open center system is explained the answer will appear.

In an open center system the pump moves oil, it does not make pressure, in an open center system oil MUST move constantly with the least resistance possible or something is gonna break. I once broke the center section of a pump when the couplers did not connect properly!

Pressure is generated when a load is placed on the system ie the loader is lifting a load. the pressure generated is only enough to overcome the load. More load, more pressure required. A relief valve prevents excessive pressure in the system

Speed of lift is controlled by the volume of oil produced by the pump usually rated by GPM or gallons per minute. GPM of pump or speed of pump.

Power beyond. A hydraulic valve usually has a supply and a return. When oil is to be "sent" to another valve a Power Beyond plug is installed. This serves two functions.. One it takes the load off the seals in the valve. 2 the oil in directed thru the valve with full flow and will not interfere with the function of the valve. Example if a 2nd valve is plumbed into the return port the valve can do weird things when the second valve is activated. Such as the loader may raise or the bucket dump. This is the reason for three hoses.

The power beyond can hook up many valves For example the loader valve to the backhoe valve to the three point valve.

When a valve uses a power beyond fitting it must have a separate return to tank, so 3 hoses or lines. BUT if the 2nd valve is taken out of the system such as taking the backhoe off two of the lines MUST be hooked together. Why? remember open center MUST flow oil. If you hook the supply hose to the tank hose you eliminate the three point hitch and oil just returns to the tank.. If you hook the correct hoses you have your three point hitch back.

Your original question was "Why are three lines needed?" I hope I have explained why. But remember each valve needs its supply, power beyond (except the last valve) and the return to tank to handle the return from the cylinder or motor.

I tried to find a diagram of power beyond but only could find super technical explanations that took a well trained Xpert to understand.

By the way an Xpert = In math you solved for the unknown or X in science class you learned a spert was a drip under pressure. So an Xpert is an unknown drip under pressure.

Have a great day.

 

[CalG]

If the valve leaks internally,...in any way,... (they all do)

that fluid MUST be allowed to return to tank.

Even if it is leakage from the return to tank circuit.

go figure!

 

[goeduck]

I look at it this way on an open center system. If you take food off of the sushi train (In line) in a Japanese restaurant, once you are done with the dish it goes in the trash (the tank). If you don't think you want the dish you leave it on the sushi train and it goes to the next guy (power beyond). If no one wants it, the last guy in line sends the whole thing to the trash (the tank). Each spool valve is like a guy sitting at the sushi train.