Cage leveling on aerial lift

[Midniteoyl]

I think you've got the answer but I can't quite understand how it works on my lift. You're saying that on your tractor that small cylinder above the boom cylinder has its input and output connected to the curl cylinder, so when the boom cylinder raises, the small cylinder is extended and forces fluid into the curl cylinder to extend in just the right proportion to keep the bucket level. That makes sense.
So when I look at my lift, there are 3 cylinders involved, I'll call them the upper arm lift cylinder, lower arm lift cylinder and cage leveling cylinder. If either of those lift arm cylinders moves, it causes the basket to go out of level unless the leveling cylinder moves the right amount in the right direction. So how are both lift arm cylinders "connected" to the leveling cylinder and what does it mean to be connected. It almost seems like I need one more cylinder to mimic the behavior of your tractor.

See if this is more like what you have:

How to Easily Design a Hydraulic Leveling System | Mentored Engineer

There are many times in my design career that I needed to translate an object without rotating. Lifting an object on a table is a…

mentoredengineer.com

>The traditional use is for platform leveling on a man lift. At the platform, there would be an upper hydraulic cylinder between the platform and the boom. This cylinder is driven by a similar lower cylinder between the boom and the riser or knuckle. It is important to note that the lower cylinder does not raise and lower the boom, it is there to tell the upper cylinder what to do.

 

[BeezFun]

I was checking the parts manual for you lift to get a better idea. It still works as I said before though.

The middle cylinder, the one mounted on what they call the knuckle and I believe you're calling it the upper arm lift cylinder, is the slave cylinder. It would be the equivalent of the smaller cylinder on the loader I showed before.

That cylinder is not actually actuated, instead it works exactly as your first paragraph of the quoted post, by forcing the fluid to extract or retract the basket cylinder as they are both connected to each other.

The parallel linkage on the lower arm, causes both arms to lift at once with the use of a single cylinder, the one on the bottom.

OK I'm getting closer to enlightenment. Here's a diagram from the manual:

When I move either cylinder A or cylinder B, the basket gets out of level. The leveling cylinder is under the basket. How do cylinders A and B interact with the leveling cylinder to keep the basket level?

 

[BeezFun]

I agree it looks like the "knuckle" cylinder is controlling the basket cylinder when the boom is raises and lowered.

It also looks like there is a valve tied to the system so you can manually control basket tilt. Which would make sense cause every lift I have been on has been that way. So it's not a "closed" system. If you do need to remove/rebuild a cylinder.....you have manual control over basket til to get it back to level and purge air out. Then it's down to automatic operation as you raise and lower

Yes there is a manual valve for basket, and it is how the air is purged. How did you it will purge air just by looking at diagram? I only knew that because the manual explains it.

 

[BeezFun]

See if this is more like what you have:

How to Easily Design a Hydraulic Leveling System | Mentored Engineer

There are many times in my design career that I needed to translate an object without rotating. Lifting an object on a table is a…

mentoredengineer.com

Great article. I am embarrassed to say I now think there is a small cylinder somewhere I haven't noticed, maybe that's the one called the knuckle cylinder. I'll check tomorrow morning, thanks.

 

[ptsg]

OK I'm getting closer to enlightenment. Here's a diagram from the manual:
View attachment 714762
When I move either cylinder A or cylinder B, the basket gets out of level. The leveling cylinder is under the basket. How do cylinders A and B interact with the leveling cylinder to keep the basket level?

Cylinder A lifts or lowers the entire boom, both the lower and the upper boom.

Cylinder B is the slave cylinder tied into the leveling cylinder of the basket.

When you lift the boom, the cylinder B extends and pushes fluid from the rod end port to the extend port of the lift cylinder. Vice versa when it lowers.

However, you can actually "force it" using the valve tied in that circuit and doing so, will make the upper boom move independently of the lower boom.

 

[LD1]

Your sketched diagram don't match the picture.

You are missing the linkage that causes the main cylinder to raise BOTH booms.

The other cylinder is just along for the ride and controls the basket articulation

 

[BeezFun]

Wow, so I've owned this lift for 10 years and don't really understand how it works. Tomorrow I'm going to stare at what's really happening when I work the different cylinders. Thanks for all the help.

 

[LD1]

Wow, so I've owned this lift for 10 years and don't really understand how it works. Tomorrow I'm going to stare at what's really happening when I work the different cylinders. Thanks for all the help.

Take a pic of the controls layout. It looks like you only have one function to raise the boom. And you cannot control cylinder B by itself as it is the slave to the basket cylinder

 

[BeezFun]

Take a pic of the controls layout. It looks like you only have one function to raise the boom. And you cannot control cylinder B by itself as it is the slave to the basket cylinder

I'll take a picture today, but I can control those cylinders separately. There's a valve for cylinder A, a valve for cylinder B, and a valve for the basket cylinder (there's also valves for slew and telescope, but they don't enter into this). That's what has me confused, I want to look at what's happening when I move A and how the linkage affects what happens to B.

 

[LD1]

What actually happens when you move cylinder B by the control?

Because looking at your first picture, it doesnt look like that cylinder is made to move independently.

Due to the linkage, if cylinder B tries to move and either raise or lower the upper arm....the linkage it is connected to will make the lower boom move also....thus cylinder A would also need to move.