Cage leveling on aerial lift

[BeezFun]

Here's the controls layout, the lever labeled boom corresponds to cylinder A in the diagram I posted above, the lever labeled arm corresponds to cylinder B. You can't see it in the photo, but there's a small lever that allows manual operation of the leveling cylinder. Inline with my toe at the bottom of the photo is the leveling cylinder, but it's hard to see through the expanded metal floor of the cage.



Here's a video of cylinders A and B operating independently. I notice that using cylinder A doesn't cause the cage to go out of level, so the leveling cylinder doesn't have to operate. I guess that's because of the geometry they chose. The cage leveling cylinder only needs to operate when cylinder B is used to raise the upper arm.

 

[LD1]

Upon further looking at it, and seeing some pictures on their website, I think I have it figured out, but I am not at a computer with a feature to draw or edit pictures to help you understand. So I'll try to explain with only words...

It looks like the upper boom can pivot between where cylinder B and where the linkage hooks to it.

So it appears that when you extend cylinder A....BOTH booms raise because cylinder B is effectively locking the upper boom into a rigid state. In this case, when cylinder A is activated....cylinder B also moves but it is controlling the basket tilt.

Due to the extra pivot point on the upper boom, you can also control cylinder B manually. And due to that extra pivot......the linkage that causes BOTH booms to move when cylinder A is activated is uneffected.

And I suspect something in those check valves and "over-center" valve is controlling basket leveling as well when cylinder B is controlled manually.

ITs a little harder to diagnose a cylinder issue on aerial equipment due to the safety DPCV's that preven the cylinders from drifting down or dropping if you blow a hose. Im not going to rule out a faulty cylinder causing your issue with the basket not wanting to remain level, because it is indeed a possibility...but would need to test them. But it could also be something in that check valve and over center valve setup. But without seeing physically how it is on the machine its hard to say

 

[LD1]

I really wish I could see this lift in person. The I still think we may be missing the "knuckle" cylinder somewhere.

Looking at the full hydraulic schematics....it doesnt look like cylinder B controls the basket at all. Because on the hydraulic schematic.....they list ram 1 and ram 2. Being both lift cylinders we are referring to as A and B.

But they are listing the knuckle cylinder separately. And in the part list/number section at the bottom right, they are calling both the cage and knuckle cylinders as "leveling cylinders". And the "knuckle cylinder" is a different part # than cylinder 2 (B)

 

[BeezFun]

I really wish I could see this lift in person. The I still think we may be missing the "knuckle" cylinder somewhere.

I agree, I've never understood what the knuckle cylinder is.

Looking at the full hydraulic schematics....it doesnt look like cylinder B controls the basket at all. Because on the hydraulic schematic.....they list ram 1 and ram 2. Being both lift cylinders we are referring to as A and B.

I agree that ram 1 and ram 2 correspond to cylinder A and B in the diagram I posted. That's the only possibility since they are connected to the valves in the cage. It looks to me in that diagram that the only thing controlling the leveling cylinder is the manual valve labeled item #7, right next to the word "cage". And so I agree I don't see how cylinder B can affect the leveling cylinder from the diagram.

But they are listing the knuckle cylinder separately. And in the part list/number section at the bottom right, they are calling both the cage and knuckle cylinders as "leveling cylinders". And the "knuckle cylinder" is a different part # than cylinder 2 (B)

Yes, that's also unclear to me. That's why I commented earlier that there must be a small cylinder somewhere that I'm missing. But I've scoured the machine and can't find any small cylinder that could be the knuckle cylinder. I'd like to try tracing the hydraulic lines that come into the leveling cylinder to know for sure where they go. But the lines go in and out of the two large boom arms with a large bundle of other hoses, it's really difficult to trace.

 

[BeezFun]

Ok, I found the knuckle cylinder by tracing hydraulic line. It's behind the label I'm pointing to in this photo.

And here's the cylinder in it's hiding place.

 

[Midniteoyl]

There it is.. The only other way that I know off doing this is with a leveling valve, but those are hard to adjust right and usually cause a lot of 'jerkyness' because they use by-passing check valves controlled by springs, thus the reason for the cylinder setup.

 

[BeezFun]

So now I understand what's going on, I also found where the leveling cylinder and knuckle cylinder are T'd together so it all fits with the schematic.

Maybe I should start a new thread, but the problem I have is an ongoing need to purge air through the leveling cylinder, so I assume the system is sucking air somewhere. How do I go about finding a leak in a system with so many paths back to dump? I've had this problem since I got it 10 years ago but it seems to be getting worse. I've replaced the hydraulic oil and filter which allowed me to inspect the large hoses connecting the oil reservoir to the pump, that all seems in good condition.

 

[Midniteoyl]

Do you also have a leak? You could dye the fluid.. StackPath

Obviously, many different brands and can be bought just about anywhere.

 

[ptsg]

That sneaky bast**rd hiding in there!! To be fair, the manual was not very clear on the location of that cylinder either.

Being that you have a valve to control the basket, should be a matter of just cycling the cylinders a couple of times and it should take the air out on the leveling/knuckle circuit.

 

[LD1]

Mystery solved. Its all starting to make sense now.

Return oil usually results in a leak and not a point in which you get air in the system. Rather a suction line from the tank to pump (if its not a submerged pump) is a source for air. But that would also cause air and jerkeyness in the other hydraulic functions.

I agree that the simplest method is to operate the basket cylinder fully both directions a couple of times and see if it starts acting better. This would best be done from the ground controls if you have a ground control for the basket