FEL wont stay up

[stan33]

Update.
Decided to replace all the hoses for safety (they are probably 30 years old at least) and take the cylinders in to be checked out and seals replaced if needed.
Will also get the control valve tested.
When I took the hoses etc off, there was quite a bit of foam (not sure if this is more than would be usual), but once the foam had cleared (half an hour) bubbles were still appearing in the oil. The tractor had not been started for around 10 days.

One cylinder had considerably less oil than the other and was harder to push back in.
All of the oil on the front end was quite a lot dirtier than at the dipstick (which looks like it just came out of the can). Overall there didn't seem to be much oil on the front end, at least less than I expected.....just a dribble at the oil cooler and the oil cooler filter and very little in the hoses.
I have sent a sample of the oil from the front to a CAT lab for analysis.
Have read that if there is a pinhole leak on the suction side, it wont leak oil but will suck air.
I'm hoping this is an air leak at the front end which will be taken care of with new hoses, if not, can anyone give me an idea of what might be going on at the back end which would cause air ingress and poor flow.

A hydraulic repair place has suggested I fit load check valves on each cylinder which will overcome any leak problem from a worn spool valve. I think I might be better (costwise) to replace the spool valve with a new Prince unit.
Thanks.

 

[LD1]

Those load checks (pilot operated check valves) will work to keep the loader up, but keep in mind that the tractor HAS to be running to lower the loader if you install them.

 

[Egon]

Nice looking oil??? does the pump put out full pressure? Any suction air leaks or screen blockage? Oil level high enough?

 

[stan33]

Nice looking oil??? does the pump put out full pressure? Any suction air leaks or screen blockage? Oil level high enough?

Don't know yet about the pump pressure as I dont have a gauge. How do I check for suction air leaks?
By screen blockage do you mean the pump filter? If so that's the next job....draining the rest of the oil out and replacing the filter (bought filter then realised they can be cleaned).
The oil level is at max and hasn't changed since I got it a few weeks ago.
I read somewhere that the colour of the oil at the dipstick can be deceptive as all the messy stuff sinks to the bottom of the sump. Which might account for the difference in colour from front to back as the oil in the loader has nowhere to settle out the particles??

 

[J_J]

Update.
Decided to replace all the hoses for safety (they are probably 30 years old at least) and take the cylinders in to be checked out and seals replaced if needed.
Will also get the control valve tested.
When I took the hoses etc off, there was quite a bit of foam (not sure if this is more than would be usual), but once the foam in the pic had cleared (half an hour) bubbles were still appearing in the oil. The tractor had not been started for around 10 days.

View attachment 441718

One cylinder had considerably less oil than the other (see pic) and was harder to push back in.
All of the oil on the front end was quite a lot dirtier than at the dipstick (which looks like it just came out of the can). Overall there didn't seem to be much oil on the front end, at least less than I expected.....just a dribble at the oil cooler and the oil cooler filter and very little in the hoses.
I have sent a sample of the oil from the front to a CAT lab for analysis.
Have read that if there is a pinhole leak on the suction side, it wont leak oil but will suck air.
I'm hoping this is an air leak at the front end which will be taken care of with new hoses, if not, can anyone give me an idea of what might be going on at the back end which would cause air ingress and poor flow.

A hydraulic repair place has suggested I fit load check valves on each cylinder which will overcome any leak problem from a worn spool valve. I think I might be better (costwise) to replace the spool valve with a new Prince unit.
Thanks.

Air in a hyd system could be from a suction hose and show bubbles in the reservoir.

Cavitation can also cause air in the hyd system.

 

[2458n]

I did not understand half of what was said. Just rebuilt my Kubota front end loader valve with no problem after 34 years of use. Kubota does not carry the parts yet no problems doing it.

 

[muddstopper]

I need some clarification, all you experts have confused me. The senario seems to be if a double acting cylinder has bad seals, that you can raise the cylinder but it cant lower., unless oil is bypassing back thru the control valve. And if the cylinder hoses are capped off the cylinder cant retract at all. Now if I am reading this right, I will just give my opinion, even tho I certainly aint an expert. If you extend a double acting cyl and it has bad piston seals, and you extend the cyl to full stroke by raising the loader arms and then somehow disconnected the hoses from said cyl and added plugs, that cyl will leak dow. The time it would take to leak all the way down would be realative to just how bad the seals are allowing the oil to bypass from the piston side of cyl to the rod side of cyl. If the cyl is left long enough eventually all the oil on the piston side would transfer from the piston side to rod side as it flows pass the seal and the cyl will completely retract or lower. Speed of fall would be regulated by how fast the fluid bypass of seals, but I assure the cyl will fall. Just because the cyl is slow to fall doesnt mean the fall can be called a spool problem. Really fast fall speeds could be a really bad piston seal just the same as it can be a bad spool in the valve. If the cyl seals are bad enough that adding pressure to the piston end allows the oil to bypass said seals, then rod would only extend to the point pressure equalizes on both sides of the cyl. No the oil can exit the cyl thru the rod end port, back to tank allowing the cyl to fully extend, but if you disconnected the hose at that point and capped both ends of the cyl, and the cyl is under load, that cyl will leak down.

 

[LD1]

Mudstopper: wrong on all accounts. The cylinder cannot collapse.

The cylinder is full of oil and capped so oil cannot exit the cylinder correct?

For the cylinder to collapse, the rod has to enter the cylinder. So I ask, where does the oil go that the rod displaces?

The rod side of the cylinder is capable of holding LESS oil than the piston side. In order to go from full extend to full collapse you are saying all the oil from the base end has to transfer to the rod end. But there is more fluid than the rod end can hold due to the rod taking up space.

Ease explain where this extra oil goes?

 

[Tx Jim]

DITTO what LD1 stated IE leaking FEL boom piston seals will not let boom settle as there's no place on rod side of cyl barrel for extra oil.

 

[LD1]

This has been discussed and explained MANY times here on TBN.

Anyone who still things piston seals can cause a loader to drift, Please read the following threads. This is just a few, but some of the ones with better discussions. Any questions you may have, or any reasons you think we are wrong, have all been addressed somewhere in one of these threads:

http://www.tractorbynet.com/forums/hydraulics/316501-loader-leak-down.html
http://www.tractorbynet.com/forums/john-deere-owning-operating/322055-bucket-drops.html
http://www.tractorbynet.com/forums/...ating/320126-leaking-hyd-cyl-400x-loader.html
http://www.tractorbynet.com/forums/kioti-owning-operating/329576-my-fel-bleeding-down.html