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

[tjc1989]

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.

Sure , I took about 50 pics or more. Unfortunately, I did not take any of the valves disassembled for cleaning and inspection. I'll enclose some of the piston and seals, the crank and piston inside the bore, and view of bottom of hydraulic assembly.

 

[tjc1989]

"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."

Yep, this thought had already crossed my mind. And actually , I hope you are right. That means I never had to repair it again.

I suspect most folks would have just repaced the piston seals and put it back together. I have to try and figure out why this is happening and the cause of the problem more than the fix. I just can't fathom these piston seals wearing out so fast, and needed to solve it. Hopefully I have.

A couple of things: I checked my warranty paperwork, and at 155 hours, the dealership shows replacing all 4 piston rings, the 2 wear rinmgs, the lip seal and the backer ring. There was no mention of checking or cleaning any of the hydraulic valves. I now have 338 hours, and its shot again. I suspect that the pressure relief valve has always been sticking or stuck. These should last more than a little over 150 hours usage. If the mechanic at the dealership had inspected the relief valve, he might have corrected the problem.

Second, I have had more than one Branson mechanic advise me to be cautious when holding an implement in full lift. Some mentioned it could cause excess heat. I don't really understand that statement. What is the difference in holding an implement up with the piston halfway up the cylinder bore, or full out in max lift? Unless, something is happening at full lift that is not midway in the bore. That is what led me to really examine the piston relationship to the bore. In the one shot I posted earlier, you can see that it doesn't take much protrusion of the piston out the cylinder that the bottom wear ring is exposed and partially out of the bore. Some people have made posts that the heat gets so great it melts the backer ring, and probably collapses the lip seal, too. Why the heat? I haven't got a real good grip on it yet. Hopefully my attention to indexing marks and attempting to keep the piston fully inserted in the bore when in max lift will alleviate that issue. Time will tell.

The Branson manual says to transport implements in the lower position. Not sure if that caution was for road safety or equipment safety.

I read some other posts, that leaves me to ponder . Some have stated that the relief valve is ONLY in play when the lift is actually lifting, and when stationary, such as when you are driving down the road carrying your brush hog or ?? , its not into play. I have no way of proving or disproving that . I would need a real detailed fluid schematic to determine that , and of course I have none.

What drives me, is that why some older tractors have thousands of hours, and no apparent rear lift failures.

But, as you said, I hopefully will never have to call on this deep thinking issue again.

One thing I have already discovered, and will probably discover more to come, is that I keep my implements off the ground on concrete cinder blocks. Since I have restricted and changed the max lift height, I can barely clear the blocks to get them off, The most obvious solution to that is shorter blocks. I did check my lift with the tiller on it to check leakdown. I shut the motor off, left it about 10 minutes, and noticed no leakdown. I could have left it longer but I had things to do.

 

[Jerry/MT]

A stuck relief valve could indeed have been the root cause of your problem. It should limit both a steady state case of an overloaded hitch and the dynamic case of a a heavily loaded hitch on a tractor bouncing around on a rough field. If the relief valve doesn't relieve, than the weakest link in the system will relieve (piston seals?).

A stuck open relieve valve or one that is constantly open due to overload will generate a lot of heat because it will recirculate high quantities of fluid through the pump which, due to pump inefficiencies, will cause the fluid temperature to rise.

After reviewing you pictures I can see where the lower seal could protrude out of the cylinder and I believe the action you took to correct this was probably correct. However that seal probably is not that important since there are three seals ahead of it and the fluid presure drops between every seal. But if it isn't going to seal anything, you can question why it was put there.

I again concgratulate you on your thorough approach to this problem. I hope you have solved your problem.

 

[J_J]

tjc1989

A relief valve, if working properly, should only be relieving if the pressure on the relief is exceeded. You can cause the relief to activate, by lifting a load that is to heavy, or hold the valve in raised position to long. If the valve is in neutral, the piston has done it's work, and the only pressure there is the pressure caused by the load. If you were to bounce that load, you might activate the relief just to relieve the over pressure if any. If the relief were stuck partially, you could raise the load, but shortly thereafter, the pressure would bleed down, and you said something about the draft control, and if it was sensing a different level set, and it would try and regain the hold position. So it would seem if that were the case, the 3pt would hic-up continuously, like you said.

Just thinking out load on all this.

You mentioned something about the heat, and why. The relief is only there to protect the overpressure, and if it has to do that 50 to 75 % of the time, that is a lot of fluid going through a small orifice for a long time, and should generate heat. If you were to take an infrared picture of that valve working, you would see the hot spots.

You had it apart, what do you think?

 

[tjc1989]

　
Jerry/MT
"After reviewing you pictures I can see where the lower seal could protrude out of the cylinder and I believe the action you took to correct this was probably correct. However that seal probably is not that important since there are three seals ahead of it and the fluid presure drops between every seal. But if it isn't going to seal anything, you can question why it was put there."
It sticks out a lot at full travel Here is another picture, clearly showing the piston protruding out the bore. Keep in mind that the rings are not on the piston while I was measuring and taking pictures. If the bottom wear ring was on the piston, it would be way out of the bore.
I agree with you. I think that the pressure relief valve stuck partially open was a real problem, and I believe it has been that way a long time. When the Branson dealer replaced the seals, and I brought it home, it was still having the hiccups, so I believe that it was stuck then.
I don't believe any of this had anything to do with draft control.
Quote "You had it apart, what do you think?"
J_J
The relief valve didn't have any real evidence of heat, other than stuck. And I know it was stuck partially open, because when I was air pressure checking the passages, just a trickle of air was flowing through the passage. After I got the valve free and removed, cleaned and reinstalled, the same air check allowed a HUGE flow of air through the passage. If no air had gone through, then I would have believed it to be stuck closed. But, I saw no heat discoloration on the valve.
Look at the picture above of the piston. There is a lot of heat discoloration aroung the lip seal and backer ring groove on the piston. So I believe it has been pretty hot at some time. Thats what led me to make changes to limit how far the piston protrudes out the bore at the bottom. Of course that picture was taken at extreme travel of the crank, rod and piston. I believe the original Branson setting most likely had the piston stopping about 3/8" short of crank contact with the case. Even then, the bottom wear ring was protruding out the bore. That can't be good.
What caused the heat discoloration on the piston, and probably the premature wear on the lip seal? Nopt sure, but I feel that me changing its travel can't hurt, by keeping the piston fully iin the bore.
On another note, I had already mentioned that I had discovered that now I wouldn't be lifting as high, and that could affect some of my implements. So I drilled a new hole today, and solved that problem. Now my lift arms don't go as low as they used to, but a quick pull of the pin and adjust the other side, and that is solved too.:thumbsup:

 

[J_J]

tjc1989,

Just thought I would check back and ask if the 3pt fix was still working, and does it still hold with no leak down.

In your breakdown, and observations of the 3pt parts, did you ever figure out if the piston was supposed to come out of the bore and expose any of the o-rings seals, or was that accidental? Now that you know it can do that, is there anything you can do about it. Did you ever talk to the engineers at Branson

Another question, do you think that the stop valve generates more heat when it allows the implement to move slow or full open/fast. Is the draft control an on/off condition.

I was also thinking that if there was a gage installed, that it would show pulses in the hyd pressure throughout the hyd system, and give a heads up on problems that may occur.
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