Need Help Understanding Theory and usage of Valves on Rear Hydraulic Lift

[J_J]

Turn the stop knob about half way out and play with it to see if there is any change. Fully closed, I believe youwill have no c ontrol. and full out, you will have fast raise and lower.

 

[Jerry/MT]

Jerry/MT , oldnslo, and J_J,

Thanks for taking the time to read and respond. To clarify, Control Valve,
Position Control, Main control. If you look at the schematics I posted, does the control valve under the bottom do all three of your answers?

In other words, is this the valve that holds position control? And regulates flow to the cylinder?

And J_J, IF the safety valve is another relief valve, Do you know how either the relief valve or safety valve could be affecting the pressure on the lift piston?

I guess I am just trying to get a good pointer to try and zero in on the correct valve to clean and inspect. Of course, I will probably do all of them.

I am going to post another schematic, showing an overview of the system.

Its another story, but the dealer jerked me around horribly on some other minor warranty work, and who knows, maybe the mechanic never even put in a new piston o-ring. But assuming he did what he said, thats always led me to believe that some sediment , cuttings or trash is interfering with one of the other valves. That would explain why he did not fix it.

Obviously, pressure is bleeding down somewhere, either past the piston, or another valve.

On my tractor, high pressure fluid goes to the FEL joystick valve, then on to the rear lift through a hose. Is there any reason to suspect trash in the FEL valve?

I would assume the problem is with a leak somewhere that is allowing your lift cylinder to leakdown and the causing the position control to respond to the resulting position change.

If you have a draft control lever, use that to raise the lift with your position control lever in the full down position.(I can do this on my Ford 4610) If the hiccup goes away but the lift drifts down, you'll verify that you have an internal leak. I'm not sure it's worth the effort to tear into the hydraulics for this problem unless you get to the point where you continually cycle the lift. The time to fix it was when it was under warranty.

 

[tjc1989]

Jerry/MT , oldnslo, and J_J,

OK, lets address these.

First Jerry/MT, my tractor draft control has no effect on raising or lowering the rear lift. I thought trhat it wouldn't, but went out and tried it anyway. With lift control lever in full down, draft control lever has no effect whatsoever.

As far as how much trouble its going to be, I would agree if it was like some have decribed on the site, such as a correction every minute or two. But mine is like 2 or 3 times a second. If I am transporting my brush hog down the road to my field, and have my front bucket on, the bucket is even popping from the rear lift rapidly correcting. Its really annoying.

Second J_J, I have previously tried the knob, full out, and full in, and everything in between. No real change.

Third oldnslo, I am tending to agree with you. Mostly because there is a change in the rear lift correcting if using the loader slightly. It seems to me that if it was just the piston in the lift letting fluid pass by, causing the lift position to activate and correct, that using the loader and creating less pressure would serve to cause the lift position to correct more rapidly because the downward load on the lift is constant, and with less pressure to keep the hydraulic piston extended, it seems it should try and correct more often. But instead its the opposite, which leads me to suspect something else, such as the control valve body or a pressure relief valve.

And that gets me back to my original question. Of what exactly the various valves are designed to do.

A couple more questions, if I may. When not using the lift or loader, what serves as a pressure relief valve in the hydraulic system? Is there something in the pump itself?

And I know this will make all of you snicker. How does the rear lift know its went down a little for the lift position to sense a change and correct it? Is there some sort of sensing device, either mechanical or electrical that senses this change? I'm just not visualizing how this can sense a change in load height.

No matter what , thanks for all the input. Believe, it helps.

 

[J_J]

tjc1989

A couple more questions, if I may. When not using the lift or loader, what serves as a pressure relief valve in the hydraulic system? Is there something in the pump itself?


When not using any hyd function, the fluid is just passing through the open center valves and returning to tank. You only get pressure when the fluid has some resistance, such as a cyl or hyd motor, and if you try and do to much, the pressure will build up and the relief valve will operate until the pressure is below the relief valve setting.

The relief could be by the pump.

 

[oldnslo]

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Third oldnslo, I am tending to agree with you. Mostly because there is a change in the rear lift correcting if using the loader slightly. It seems to me that if it was just the piston in the lift letting fluid pass by, causing the lift position to activate and correct, that using the loader and creating less pressure would serve to cause the lift position to correct more rapidly because the downward load on the lift is constant, and with less pressure to keep the hydraulic piston extended, it seems it should try and correct more often. But instead its the opposite, which leads me to suspect something else, such as the control valve body or a pressure relief valve.

And that gets me back to my original question. Of what exactly the various valves are designed to do.

A couple more questions, if I may. When not using the lift or loader, what serves as a pressure relief valve in the hydraulic system? Is there something in the pump itself?

Not knowing how your tractor is plumbed I would hazard a guess and say that the relief in your control valve is the system relief for your loader. If your loader is plumbed before the 3PH then it should have a relief valve in its control valve also.

And I know this will make all of you snicker. How does the rear lift know its went down a little for the lift position to sense a change and correct it? Is there some sort of sensing device, either mechanical or electrical that senses this change? I'm just not visualizing how this can sense a change in load height.

Not sure exactly how the linkage works but it either internally or externally looks at the valve input position Vs the lift arm position. Again I can't determine how this linkage would connect to the control valve.

No matter what , thanks for all the input. Believe, it helps.

I looked at the parts description for your control valve and like most the descriptions leave some thing to be desired. What I could not determine is which spool is the main input from your control lever. One of the other spools would then be the position control. If your are a retired tranny mechanic I suspect you could carefully remove this valve package and then follow the flow paths through the casting and probably make some sense out of which spool controls what. ALL Spool valves leak, how much depends on the casting, spool bore clearances, overlap of spool and other factors. Cycling every two to three seconds is a fairly big leak. Can you get a rough idea on how much the arms move each time it cycles. I.e how far does it drift down before it corrects itself?

Compared to an automatic this should be simple.

Best of luck

Roy

 

[Jerry/MT]

Jerry/MT , oldnslo, and J_J,

OK, lets address these.

First Jerry/MT, my tractor draft control has no effect on raising or lowering the rear lift. I thought trhat it wouldn't, but went out and tried it anyway. With lift control lever in full down, draft control lever has no effect whatsoever.

As far as how much trouble its going to be, I would agree if it was like some have decribed on the site, such as a correction every minute or two. But mine is like 2 or 3 times a second. If I am transporting my brush hog down the road to my field, and have my front bucket on, the bucket is even popping from the rear lift rapidly correcting. Its really annoying.

Second J_J, I have previously tried the knob, full out, and full in, and everything in between. No real change.

Third oldnslo, I am tending to agree with you. Mostly because there is a change in the rear lift correcting if using the loader slightly. It seems to me that if it was just the piston in the lift letting fluid pass by, causing the lift position to activate and correct, that using the loader and creating less pressure would serve to cause the lift position to correct more rapidly because the downward load on the lift is constant, and with less pressure to keep the hydraulic piston extended, it seems it should try and correct more often. But instead its the opposite, which leads me to suspect something else, such as the control valve body or a pressure relief valve.

And that gets me back to my original question. Of what exactly the various valves are designed to do.

A couple more questions, if I may. When not using the lift or loader, what serves as a pressure relief valve in the hydraulic system? Is there something in the pump itself?

And I know this will make all of you snicker. How does the rear lift know its went down a little for the lift position to sense a change and correct it? Is there some sort of sensing device, either mechanical or electrical that senses this change? I'm just not visualizing how this can sense a change in load height.

No matter what , thanks for all the input. Believe, it helps.

SO your tractor does not have combined position and draft control.

If you are getting the position reset 2-3 time per sec you have a major leak or whatever signals the position feedback to the control valve s giving an erroneous feedback signal. I take it you don't have a service manual, is that correct? If you don't you are in the hurt locker!

Is there any way you can observe the goings on in the hydraulic compartment with the system operating? If so you can visually see the leak. If not, I suspect the lift cylinder is leaking, the exhaust from the lift cylinder has a leak ahead of the exhaust portion of the valve OR the relief valve is stuck open because some trash is stuck in it. That's just intuition on my part. Do you have hydraulic circuit diagrams? They can help to pinpoint possible sources of the leak.

Put something heavy on the three point lift it all the way up, leave the control lever in the full up position, and then shutdown the tractor and time how fast it drops. This can give you an idea of the magnitude of the leak. Unfortunately it still doen't tell what's leaking it just verifies the leak.

If the leak is rather slow (<15 minutes to fall completely is a guess) the other possibility is that the feedback device that denotes that there has been a position change maybe the problem. It's most likely driven off the rockshaft. It could be a cam or ?. if you don't have a quick leak down of the three point hitch, that could imply it's not a leak but some erroneous feedback is going to the valve that's causing it to reset the position.

Whatever you do, don't take the liftcover off until you have an idea what the problem is becausse you'll lose the ability to trouble shoot the system.

 

[tjc1989]

Thanks for all the input, guys. I didn't really have a good understanding how the thing worked before this post. I mean, I knew how hydraulics worked in general, but had a hard time grasping what went on when something was lifted, and the how system could hold it in place, and correct itself if it leaked off and changed position.

I went ahead and tore it down. Every piece was inspected, measured, thought on extensively, photographed, and questioned what it did and why.

Since I had no manual, along with help from this site, I had to self teach. I'm the sort that can't really fix anything if I can't visualize it working.

So, here is what I found. The 4 rings on the hydraulic piston had some wear, and the lip seal or u-packing was the worst. It didn't appear wore out, but I replaced all of them anyway. The stop valve, control valve, safety valve and relief valve were cleaned and inspected. Oil passages were air pressure checked. Of all the valves, only the relief valve was a problem. It was stuck in its bore, and had to blown out with air pressure.

Because I had read several references on this forum about cautioning operating at full lift for very long, I wanted to know why. I rolled the lift arms full open until the crank hit the case inside. I then indexed this externally on the lift arms for reference, then while the crank was against the case wall, I inserted the piston, and examined where the piston was in relation to the cylinder bore. It extended out past the cylinder bore nearly an inch. Then I rolled the lift arms down until the bottom of the piston was even with the cylinder bore, and made index marks for that also, so that I would know where the ideal max lift spot was.

I thoroughly examined how the position control and draft control were designed to work, mad drawings and thought some more.

I installed the new piston seals and put it all back together. Cranked her up and watched where the index marks lined up, and felt that it was lifting too far, because it was going past my index marks, and I knew the piston was protruding out past the cylinder bore. I adjusted the position control to force the lift to stop at my index marks. I lose about 2 inches of lift this way, but feel that the damage people say happens to the seals should be considerably less, since piston does not now protrude out past the cylinder bore. Without taking it apart, I would never have been able to know where the piston was located at what lift position.

So my hiccuping problem was caused in my opinion by 3 things. Worn piston seals, stuck pressure relief valve, and hydraulic piston pushed too far out of cylinder.

Even though I haven't checked it with an implement, it lifted my weight while standing on the hitch as smooth as a baby's butt. Up and down several times, really great. No bumps or hiccups. When I shut it off, I left the lift in a near full up position. I went out to the shop a little while ago, to see if it had bled off any, and does not appear to have moved any at all, after 6 hours. That's the first time since right after I bought the thing new that it would do that. :thumbsup: Time will tell I guess, if my fix is a long one.

 

[mmurphy]

tjc1989, thanks for letting the guys know how it went, in the long run it helps everybody. I am sure you probably got it fixed, and now I seen another guy who was having same problem will know what to do.

 

[irvingj]

Great story, great fix! Any possibility of posting those pics? My 2310 doesn't even have draft control (at least I don't think so), but I still love learning about this stuff! Thanks very much for sharing your troubleshooting experience.

 

[Jerry/MT]

Thanks for all the input, guys. I didn't really have
I then indexed this externally on the lift arms for reference, then while the crank was against the case wall, I inserted the piston, and examined where the piston was in relation to the cylinder bore. It extended out past the cylinder bore nearly an inch. were designed to work, mad drawings and thought some more.


When I shut it off, I left the lift in a near full up position. I went out to the shop a little while ago, to see if it had bled off any, and does not appear to have moved any at all, after 6 hours. That's the first time since right after I bought the thing new that it would do that. :thumbsup: Time will tell I guess, if my fix is a long one.

There's not nececessarily any harm in having part of the piston come out of the cylinder as long as it doesn't cock or hit anything that it's not supposed to. On my Ferguson TO-30, the end of the piston goes past the end of the lift cylinder and pushes on the linkage that puts the control valve into the neutral position so in that case it is designed to do that. As long as your system works properly, I doubt that there is any harm in doing what you did.

A better test for leak down would be to put a heavy implement on the three point and then shut down with the lift lever full up and time the leak down.

You're very persistent and analytic and I applaud the fact that you systematically looked at everything and deduced the possible causes of your problem. Unfortunately, as perverse as these systems are, you will probably never have any further personal use for the knowledge you gained in this process(Grin). However, you will be able to advise others.
Great job!