Did I bust something on the loader hydraulics?

[ljjhouser]

Does it do the same thing when it is running?

 

[npalen]

If the bucket not being level had anything to do with the hydraulic fluid system it would have gone away just by hitting top and bottom of lift travel a couple of times. Something is bent or shifted on that one. The fact that it goes level at the top and bottom is just the loader hydraulics flexing it back the other way, but not flexing it past its 'yield strength', so when you release it just springs back to 'bent'. With careful setup you might be able to use the loader hydraulics to 'unbend' it just like people do with their SSQA cross-tubes.

The bucket rocking so easily while the valve is in the 'neutral'/middle position likewise COULD be air but that should have rectified itself just by fully extending and retracting the cylinders several times. What makes me think it still IS air in spite of that theory, is how easily it moves. Even if a piston seal or a spool valve leaked, you still have to 'pump' fluid through that 'orifice' to get the cylinder to move, and basically ALL of the fluid in that circuit has to move to do it. Even without much restriction from the leak/orifice, it's still a fair amount of inertia and more like stirring honey than just flopping around like in that video. If you consider something like leaving the bucket tipped down a little, putting the loader in float and letting it hit the ground, turn off the tractor, and then pull the bucket curl valve, the bucket will 'settle' to the ground much slower than the movement shown in that video, and that's with the valve fully open with the whole weight of the loader and part of the weight of the bucket on it, not just something 'leaking' with one measly boot pushing down on it. The system has a LOT of air in it!

As for how the air got in there and then.. never left or never stopped reappearing, i'd be especially suspicious of shaft seals on the cylinder glands, valve body handles/levers or at the pump. A lot of hydraulic pressure seals are directional lip seals, which means their ability to seal goes up with the pressure pushing them against the shaft, and down when that pressure goes down. They're also bad at resisting any pressure from the 'outside', which is usually just atmospheric pressure so not usually a problem.

But think of this. This loader works when the tractor runs. When you pressurize circuits, it more or less becomes normal. Once you fully relieve the system pressure, it becomes wonky and may only do so after sitting for a while. My theory is that a directional lip seal is now allowing air to suck into the system when the pressure drops to 0, but then seals again as soon as you MAKE pressure in the system. I have seen something similar to this on leaky cylinder gland seals, as im sure many others have. They seal 'better' when retracting the cylinder because pressure is forcing them against the rod, but leak profusely upon extension because no real pressure builds in that chamber when the control valve is open on that side.

Just because hydraulic pressure drops to 0 doesn't mean there's nothing to generate 'suction' in the hydraulic system. The weight of any hydraulic fluid being held above the sump that has a free path to flow back to the sump is only being held in the lines by the ability of the system to keep air out of shaft seals. If you picture sticking a straw in a drink, covering the end with your finger and picking up the straw, the liquid only stays in the straw because your finger is sealing against that 'suction'. So my perhaps left field theory is that you might have damaged a directional lip seal which is allowing the weight of the fluid held above the sump to suck air into the system every time the system pressure drops to 0. The loader itself never moves because it's already on the ground, only the fluid in the system moves as some migrates back to the sump and is replaced with air. Once you start the tractor, the pressure causes damaged seal to seal again, and loader will more or less immediately work, although you might notice its initial response to the first lever inputs is delayed (squeezing the air pockets before making real pressure), and its ability to hold weight is 'springy' (air spring) until you've chased all that air back to the reservoir and purged it, at which point it becomes 'solid' again. Until it's parked for a while!

You make some good points about how air gets into a "sealed hydraulic system" including how air can get past a unidirectional seal.

I'll mention again the scenario of dropping the loader and/or bucket quickly, especially with a heavy load on it, where the pump can't keep up with the volume of fluid needed to fill the rapidly extending or retracting of the bucket and/or lift cylinders.

There is a lot of vacuum created in the "other side" of the cylinders during the "drop" and that vacuum is probably sucking air past the seals and/or the pump.

Brian (FitRiteHydraulics MtnViewRanch) has mentioned, on occasion, cycling the 3PH top link cylinder slowly when purging air so that the pump can keep up with 3PH load trying to overrun the pump. Same principals apply here.

 

[Zebrafive]

I've had 3 tractors and when the bucket is sitting on the ground with the front edge up a bit they all did exactly the same thing when you stepped on it . There is no resistance because the controls are in neutral and the fluid is able to flow with no resistance.

It could be play in the pins, linkage, that lets the bucket rock. Or if the hydraulic fluid cooled from when the tractor was parked, the fluid might have contracted enough for some "hydralic play" too?
On the original post, I guessing twisted the loader frame or a mount moved, if not tight enough bolts holding it.

 

[Tx Jim]

npalen
Would performing what I previously stated in my previous reply(#8)[/quote]I'll suggest to raise FEL boom then curl/retract bucket several times utilizing tractor hyd system.[/quote] accomplish what Brian(FitRiteHydraulics MtnViewRanch) stated & accomplish this task?









[

 

[Tx Jim]

Well I must eat crow after Tx Jim set me straight i knew he was correct. I thought I'd better check again stepped on the bucket rocked it and sure as hell it looked like the cylinder rods moved an " or so. I knew it wasn't possible so i looked real closely where the rod came out and sure a heck it never moved. Rocking it back and forth I realized the edge of the bucket reflection on the chrome rods going up and down gave the impression they were moving. Thank you for the common sense post Jim.

You're Welcome.
Another possibility I mentioned earlier is nut holding bucket cylinder piston on rod stripped the threads & piston is loose on cylinder. I think one or both bucket cylinder piston seals needs to be visually inspected.

 

[rScotty]

Usually via the pump.

Edit: Also, on a loader with a lot of weight and letting the it down quickly and then closing the valve. The pump can't keep up.

Both right. You'll get air entrained into the hydraulics fluid from any air leak in the suction side. Then on the pressure side any movement that results in a sudden drop in fluid pressure allows the entrained air to form air pockets. The air will eventually clear up when the oil heats up and circulates a few times.

 

[Vigo327]

Brian (FitRiteHydraulics MtnViewRanch) has mentioned, on occasion, cycling the 3PH top link cylinder slowly when purging air so that the pump can keep up with 3PH load trying to overrun the pump. Same principals apply here.

I have an electro-hydraulic top link and i have to set the implement to the ground before extending that cylinder to keep the pump (which is on the cylinder) from getting unhappy.



Regarding the OP's situation, i dont think the air got in there ONLY during the actual incident because it would have cleared up just by running the cylinders in and out enough. I suspect it is also getting air in while sitting still. But glad to hear of some other possibilities here to add to my 'diagnostic repertoire'.

 

[npalen]

npalen
Would performing what I previously stated in my previous reply(#8)

I'll suggest to raise FEL boom then curl/retract bucket several times utilizing tractor hyd system.[/quote] accomplish what Brian(FitRiteHydraulics MtnViewRanch) stated & accomplish this task?









[
[/QUOTE]
Yes, but must be done slowly and repeated several times especially when dropping the boom.
Also, I don't think the air in the system has anything to do with the log in grapple incident.

 

[Tx Jim]

Has it been established(VERIFIED) that any air is in JCoastie's FEL hyd system & I OVERLOOKED that FACT? Thread originated about bucket control circuit not boom circuit.

 

[DieselBound]

Shouldn't ever take much time to get air worked out. Work it well and it'll purge pretty quickly: think "GPM."

It was an EVENT that caused this. Understand those dynamics. Look at what forces would be applied to various parts on the loader.

As was stated, might be best (and I might think of doing this myself!*) to SLIGHTLY loosen all the mounting hardware on the loader while it's lowered and holding weight of the tractor and then re-tighten. I've heard people say they've either pulled or pushed on one arm to flex/"bend"- I'd be wary/nervous about doing this.

* My Kitoi has had an un-level loader since day one. Dealer says that they replaced it (and the saddles): I don't trust anything they say- I wasn't able to get the serial number for the loader. I later discovered that it's not as bad as I thought as the front "guard" is actually slightly off-level (I'd have to loosen it and perhaps drill out the mounting holes in order to shift).