i have already pulled the cap and disassembled/cleaned that valve. everything seems in tact, but i guess that doesnt necessarily mean its good.
3 point hitch wont lift
- Thread starter ronr
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North Idaho Wolfman
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Well, I see we have a hard-head case here
! Won't listen to one of the most experienced Kubota mechanics on here and won't avail himself of a free WSM.So, I'm probably wasting my fingers and time here. One of the items in the WSM troubleshooting table for hitch doesn't lift is Relief Valve spring broken. In the diagram below, taken from the WSM, you'll see 2 relief valves. The green one is in the priority/diverter valve body you've been obsessing over.
The blue one is in the 3PH valve body somewhere. Schematically, you can see it would limit the pressure to the 3PH and nothing else. Then looking at the lift cylinder, #9 in the diagram, you'll see that the control valve etc. would prevent back flow from the cylinder, letting it fall, and the relief valve is not involved in that part of the circuit.
Hope that helps.
yes i have. the linkage under the cap is all in tact as well. the valve seems to work correctly. if i get the arms up, and drop the lever half way down, the arms drop about half way and hold. it will hold weight at the desired height was well. it just wont lift it back up. the circled port in this pic is where the fluid feeds the piston. with the cap off, when i run the lever it does push fluid to this port, but i can very easily plug that port with my thumb and hold it back ( full throttle, lever maxed "up"). seems i can do that same on the line that actually feeds the valve assy you posted.
In post #11, he said he checked it, but that certainly is something to look at again. He has the WSM available to follow.
that helps a lot! sorry, not being hard headed or not listening here just trying to wrap my head around how the system works. maybe my wording came across wrong. i guess my google skills arent that great either, as i cant seem to locate any WSM for this? do you have a link? i did find some for sale, but i guess ive had to many bad experiences with manuals being inaccurate and causing more confusion than anything. maybe thats just the isolated to the industry im in...Well, I see we have a hard-head case here
So, I'm probably wasting my fingers and time here. One of the items in the WSM troubleshooting table for hitch doesn't lift is Relief Valve spring broken. In the diagram below, taken from the WSM, you'll see 2 relief valves. The green one is in the priority/diverter valve body you've been obsessing over.
The blue one is in the 3PH valve body somewhere. Schematically, you can see it would limit the pressure to the 3PH and nothing else. Then looking at the lift cylinder, #9 in the diagram, you'll see that the control valve etc. would prevent back flow from the cylinder, letting it fall, and the relief valve is not involved in that part of the circuit.
Hope that helps.
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TheOldHokie
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I did not read all of this discussion but if the oil delivery pipe wont build pressure when blocked the problem is upstream. A pressure test at the outlet of the selector valve mounted on the pump he selector valve up front
Dan
If this is the valve on your tractor it has a pump pressure relief built into it. Under normal operating conditions there should be no flow coming out the relief nipple. Connect a pressure gauge to the 3pt outlet and you should read pump pressure.
Dan
Ron, here's the troubleshooting table. I was going to suggest checking the piston and cylinder, but if that was the problem it wouldn't stay up when you lift it manually.
I've had a bad experience with on-line manuals also. But if you go to KubotaBooks you can find one for your tractor. Go to Tractor Owners Manuals and up near the top there's a file ending in WSM. I think there's also an Operator Manual. This is not an official Kubota site, so the manuals may not be the latest, but they're generally helpful.
If you can, I'd PayPal the guy the $2 he suggests.
i only have the parts manual from kubota's site.
thanks Dan, yes that is exactly the valve. i will do a pressure test there as soon as i can. am i mistaken that the pressure relief in this valve would also provide pressure relieve for the loader functions and power steering?
Disclaimer: I also have not availed myself of this workshop manual. Just an ASE master tech going on 20 years who hasn't found tractors to be more complicated than cars.. yet! Just jinxed myself though, didn't i..
A flow divider can only divide from a higher pressure to a lower pressure area, as far as im aware. You can see the relative pressure limits on this diagram of the valve on my b8200 which suggests the flow divider needs a minimum ~85psi pressure differential/delta to function. If the 'downstream' systems were to obstruct/dead-head for some strange reason (like disconnecting a hydraulic quick disconnect without changing the directional valve etc) the main relief WOULD open but it's not exactly setting the operating pressures for those circuits. Those are dictated down to a certain point to 'protect' or ensure the function of the flow divider.
Yes, but.. not exactly. The power steering kind of needs to have its own pressure regulated lower than the main system pressure for a flow divider to do its job. Otherwise you could have a situation where bumping the steering to its limit of travel or turning against a rock etc would cause the main pressure relief valve to open, which while it wouldn't necessarily STOP the loader it would certainly drastically drop its speed if it happened to be moving. Could potentially cause a dangerous situation if it was heavily loaded and then 'jerked' due to a change in hydraulic flow from the main relief opening. That's my understanding, anyway.
A flow divider can only divide from a higher pressure to a lower pressure area, as far as im aware. You can see the relative pressure limits on this diagram of the valve on my b8200 which suggests the flow divider needs a minimum ~85psi pressure differential/delta to function. If the 'downstream' systems were to obstruct/dead-head for some strange reason (like disconnecting a hydraulic quick disconnect without changing the directional valve etc) the main relief WOULD open but it's not exactly setting the operating pressures for those circuits. Those are dictated down to a certain point to 'protect' or ensure the function of the flow divider.
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ok, that makes sense. so..the next steps... i will chech the feed pressure supplied by the pump and see what the pump is producing. i will also check that the relief valve for the pump is not tripped for no reason, and let you all know what i find.Disclaimer: I also have not availed myself of this workshop manual. Just an ASE master tech going on 20 years who hasn't found tractors to be more complicated than cars.. yet! Just jinxed myself though, didn't i..
Yes, but.. not exactly. The power steering kind of needs to have its own pressure regulated lower than the main system pressure for a flow divider to do its job. Otherwise you could have a situation where bumping the steering to its limit of travel or turning against a rock etc would cause the main pressure relief valve to open, which while it wouldn't necessarily STOP the loader (you'd still have whatever flow the pump could make at the pressure relief setting) it would certainly drastically drop its speed if it happened to be moving. Could potentially cause a dangerous situation if it was heavily loaded and then 'jerked' due to a change in hydraulic flow from the main relief opening.
That's my understanding, anyway. A flow divider can only divide from a higher pressure to a lower pressure area, as far as im aware. You can see the relative pressure limits on this diagram of the valve on my b8200. If the 'downstream' systems were to obstruct/dead-head for some strange reason (like disconnecting a hydraulic quick disconnect without changing the directional valve etc) the main relief WOULD open but it's not exactly setting the operating pressures for those circuits.
Did i miss whether you said you got the tractor like this, or you had it working before?
One possible simple thing that could cause this would be if you switched the 'neutral' and 'tank' connections to the loader.. i think..
Instead of feeding the 3pt ALL the flow that wasn't used by the loader, it would only feed the 3pt the difference in flow between the two sides of a hydraulic cylinder (rod end has smaller volume because the rod is taking up some of the space etc).. which would be almost nothing and would ONLY be present when the loader cylinders were moving.
If this were the case it would probably be identifiable just by markings on the loader valve. But it would also be testable by trying the 3pt while running all the various loader functions and see if one of them suddenly makes the 3pt move (slowly). The fact that the 3pt currently moves extremely slowly with no force would probably just be the flow that leaks internally to the tank return section in the loader valve assembly.
I hope this is it because it's so simple to fix, but I feel a lot less confident on this one so I hope someone will be along to shoot me down if this is completely wrong.
One possible simple thing that could cause this would be if you switched the 'neutral' and 'tank' connections to the loader.. i think..
Instead of feeding the 3pt ALL the flow that wasn't used by the loader, it would only feed the 3pt the difference in flow between the two sides of a hydraulic cylinder (rod end has smaller volume because the rod is taking up some of the space etc).. which would be almost nothing and would ONLY be present when the loader cylinders were moving.
If this were the case it would probably be identifiable just by markings on the loader valve. But it would also be testable by trying the 3pt while running all the various loader functions and see if one of them suddenly makes the 3pt move (slowly). The fact that the 3pt currently moves extremely slowly with no force would probably just be the flow that leaks internally to the tank return section in the loader valve assembly.
I hope this is it because it's so simple to fix, but I feel a lot less confident on this one so I hope someone will be along to shoot me down if this is completely wrong.
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thats a great point. it didnt work when i got the tractor and i have not removed the loader from the tractor or verified the piping is in the correct location. i do wonder if the loader spools would work correctly if that they were backwards? then again, with the loader, if i try to dump the bucket while raising the bucket arms it wont do it...and as i type this i realize this could be a pump volume issue all along? im not familiar with how much power the bucket should have i assumed that by design it just didnt have stones enough to raise & dump at the same time...now i wonder?
TheOldHokie
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The pressure relief in the hydraulic outlet block limits the inlet pressure to all down stream devices.
Dan
TheOldHokie
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In general:
- The neutral line is blocked when a spool is shifted and all exhaust oil flow is routed to the tank
- When all spools are in neutral all pump flow is routed to neutral (power beyond) and there is no flow at the tank port.
But that behavior can vary by valve design. For example the boom spool on the LA525 loader valve routes cylinder exhaust oil to neutral so down stream functions (e.g. the 3pt) are not blocked. The bucket spool on the other hand routes exhaust oil to tank on curl and loops it back to the baseend on dump to speed up actuator movement. That blocks all downstream functions.
Rather than speculate on these scenarios I'd suggest pressure tests starting at the outlet port on the hydraulic outlet block and moving downstream in stages until you find a point where pump pressure is lost. The problem will be between the last two test points. Then you can start looking in that section for a defective device or misrouted plumbing.
Dan
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TheOldHokie
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Moving the selector valve to the position shown in the picture will take the loader completely out of the circuit.
Dan
He said he's tried that, but at this point it's worth re-tracking.
Something awful strange would have to be going on in that diverter to be causing this issue.
Hope you can help.
TheOldHokie
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Crud holding the relief poppet in that diverter open would kill pump pressure. I almost always start with a pump output pressure test.
After further thought it occurred to me that a stuck inlet relief on the loader valve would do the same. Even with the selector in the horizontal position the loader valve would be getting reverse flow and pressure via the power beyond port and if the inlet relief is stuck it would unload the pump to tank. Again- a pressure test would show no pump pressure.
Dan
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