Tractor pump is too big for backhoe valveset, how to fix?

[hirsch56]

I do not understand the reluctance to connect things correctly.

But whatever.

No reluctance from me, J.J. That's why I'm here, and you seem to have the most knowledge. Please be patient with me. It will be at least a month before I can get to working on it much, anyway. Right now I am trying to gain knowledge, so when I can work on it there is a good chance it will come out right. I have to get the mower done first, I work most of the day, and take care of my disabled wife most of the remainder.

I was under the impression that I do not need PB if I don't intent to use more than one implement at a time. I'll put the PB sleeve that came with it into the Loader valve (I have those instructions that came with the loader), but I don't have one for the BH valve. Not sure if it even has that possibility. There are 2 INs and 2 OUTs on the BH valve, but one set is permanently blocked by mounting to the frame. Since each is just around the corner from its twin, I assume they both go the same place and are just conveniences for different mounting. Of course I could be wrong. This BH originally was run by a PTO pump, but the shaft broke (my bad!), so I plumbed it to the remotes.

I don't yet understand how the 3PH relates to this problem. Are you telling me the 3PH is fed from the remote return line, so when I max up the hitch, it backs full pressure into the BH and Loader? If that is the case it is no wonder the caps blow out, because there is no stop on the hitch lever. I just pull it up until it loads up the engine, then back off. Do I need to put the 3PH first in the series instead of last? Is that even possible?

There is indeed a port on the tractor which seems to be a sump return. It is presently plugged. If I return the Loader and BH in series to the sump there, will the 3PH operate?

Sorry, I don't have a good way to get a picture which shows much except black. Thanks for sharing your knowledge and experience. I don't have a good manual for this tractor. The rear remotes have long ago been removed and I am using the ports underneath. I got it that way.

 

[J_J]

I don't yet understand how the 3PH relates to this problem. Are you telling me the 3PH is fed from the remote return line, so when I max up the hitch, it backs full pressure into the BH and Loader? If that is the case it is no wonder the caps blow out, because there is no stop on the hitch lever. I just pull it up until it loads up the engine, then back off. Do I need to put the 3PH first in the series instead of last? Is that even possible?

Yes, the 3pt was fed directly from an internal path, or from the remotes.

The 3pt does have a neutral position, which locks the cyl from movement.

Can you show a picture of the side ports and the way you connect the BH now.

Your hyd system is an open center sys, and all valves are connected in series.

I have seen tractors with two lines going to the back and some with three lines going to the back.

Your 3pt will always be the last circuit on the tractor as the 3pt neutral selection will just dump to tank, and the cyl fluid will dump to tank when the 3pt goes down

However, you could dump the BH fluid direct to the tank.

One of those rear ports is a pressure port, and one of them is the return port. If there are three ports, one may be the sump port.

You can connect hydraulics different ways if you are smart about it, just depends on the final expectations.

 

[hirsch56]

I'll try and get some pics and a diagram this weekend if I don't have to work and the weather cooperates. Thanks for your input - all of you.

Believe it or not, I actually aced a Fluid Power class in college, but those labs were pretty well contrived to get across basic concepts, and not really targeted to practical application or multiple cylinder circuits.

 

[Farmerford]

Seems to me that JJ identified the problem and solution:

If you are working the backhoe off of the remotes, then you have a two-hose connection to the backhoe valve. Whether the backhoe valve has a power beyond plug installed or not, if you have only one outlet hose from the BH valve, whether it connected to the "tank" port or the "power beyond" port (PB or PYB) of the BH valve, if fluid can't flow freely through that outlet hose then the pump will load up, the system relief valve (hopefully just downstream of the pump) will open to protect the pump, and the engine will slow to the load.

If the BH valve outlet hose is connected to the "out" port that pressure build up in the BH valve will occur in the exhaust bores through which the spool valves pass to reach the control lever or spring. The o-rings around the spools as they exit the valve body are held in place by the dust covers you mention. But those o-rings and dust covers are designed to withstand at most 300-500 psig. So the excess pressure makes them bulge.

So, the ultimate problem is that the outlet hose from the BH valve back to the remote valve does not provide a clear path for the hydraulic fluid to return to the tank/reservoir/transmission. It it almost certain that the return hose from the remote valve runs to the input or pressure side of the three point hitch valve. Thus when the TPH valve is activated the fluid from the BH valve is directed to the TPH ram which raises the TPH. Depending on the load on the TPH, the pressure build up could easily exceed the 300-500psig limit of the exhaust bores in the BH valve.

Furthermore, if the TPH control linkage is out of adjustment, and you raise the TPH to the maximum, the TPH valve does not shift to neutral, but instead continues to direct fluid to the ram, which of course can not move because the TPH is at the highest point.

You can test this theory without a gauge by disconnecting the BH from the TPH, but leaving the hyraulics hooked up. Then lower the TPH control handle completely, so that the TPH falls all the way down. If the BH valve then leaks, but the TPH does not rise it is (almost certainly not the TPH). But if the BH valve leaks when you raise the TPH to the maximum and keeps leaking it is almost certain that the TPH linkage adjustment is incorrect.

Note that if the TPH linkage adjustment is incorrect, it means there will always be back pressure in the BH valve. If the TPH linkage adjustment is correct, there will still be back pressure in the BH valve while the TPH is being raised with a load on it.

Now, all the above does is explain what is happening. Even if the TPH linkage is out of adjustment, once you adjust it you will still have back pressure in the BH valve when you raise the TPH with a load on it. So the answer to the problem is just as JJ said, you need to convert the BH valve to power beyond, at which time you wlll have three hoses coming from the BH valve. The power beyond hose will go back to the remote valve, and the "tank" hose will do directly to the tank/reservoir/transmission.

Look forward to getting pictures.

 

[hirsch56]

"Just when I thought I was out, they pull me back in!"

Yes, I understand that the problem is overpressure back up the line when the 3PH is loaded or tops out. I'm pretty sure the linkage is correct, because when I leave the 3PH lever in one position, the 3PH stays put without moving and there is no extra noise. I'll need to rig some sort of stop so the lever cannot go past the top, but the pressure could still exist due to the weight on the hitch.

OK, now I think I understand the PB hookup. What I think you are saying is that using PB requires 2 hoses at each valve input? One receives the supply (IN), and the other feeds downstream (PB)? So PB is similar to a Tee, but prevents backpressure? Then each valve's OUT port should go to sump (Tee should be OK there). That would make a separate flow path through each valveset. My misperception seems to be the definition 'series'. I thought series meant that the same fliuid goes through every valve, but apparently not?

 

[J_J]

PB is not a tee it is a single path through each valve.

Series is series anyways you look at it. The useful fluid that you want each valve to see is via the PB port, not only can handle the high pressure, but that is the flow path from PB to IN port of next valve. The last valve in the hyd system, is normally the 3pt, and it just dumps to tank.

The OUT ports are for the cyl or motors expended fluid with no of very little pressure involved. The ports can be tied together, but must considered the GPM, and size the hose correctly.

The 3pt lever should be left in the neutral position.

In the raise position full up, fluid is filling the cyl until it meets the load resistance, and if the cyl is fully extended, the relief will sound off and the total series hyd line will be at full pressure, somewhere around 2500 to 3000 psi.

This forum was not designed for hydraulics 101, so it is up to you to do more legwork/homework.

If you were to install a gage where you can see it, you can tell at anytime whether pressure is being generating. If a cyl is being used, and about how much load. If the cyl max's out, you are looking at relief pressure.

My post are mostly trying to keep things straight and correct things that need correcting.

 

[hirsch56]

I'm not sure what you mean by Neutral on the 3PH. The lever moves up and down, and stays where you leave it, and the hitch follows the lever. So if I pull the lever full up, the hitch comes full up, and if I push the lever to halfway, the hitch goes to halfway, and the hitch stays wherever the lever stays. If I push the lever full down, the hitch drops all the way. At full down there is no indication of stress, but if I pull it past full up, the motor loads. If it helps to make more sense, this series of JD is basically just an 80's Yanmar painted green. The hitch lever never returns to a Neutral position, it just stays where you leave it and the hitch mirrors the lever position. The Loader and BH valves all return to Neutral when I let go, but the 3PH is different on this tractor.

I'll do some more research about PB, but I think I understand it now. PB daisy-chains the pump flow from input to input, so each valve can take what it needs without the line losing pressure, so long as the gpm of the pump is not exceeded. The biggest question now seems to be whether or not the BH valveset has it or can get it.

 

[J_J]

No, you can not make a PB port.

Show us a picture and maybe we can tell you determine if you have a relief. .

You said it yourself, when the lever is about halfway, the 3pt hitch stops. That is neutral, when no fluid is going into the cyl and none is coming out. My Kubota lever stays where I leave it.

You should be able to stop the hitch anywhere between full up and full down.

In an open center hyd system, there is no or very little pressure in a line until some cyl is activated, or a hyd circuit is deadheaded. .