Hows does a float circuit work

[Industrial Toys]

Seems to me that if the cylinders in that floating circuit were moving back and forth, both plumbed to the tank at that instant, you would get air in that circuit in short order. You can't suck oil out of the return port.

Could be wrong, what do I know?

 

[beemerphile]

Seems to me that if the cylinders in that floating circuit were moving back and forth, both plumbed to the tank at that instant, you would get air in that circuit in short order. You can't suck oil out of the return port.

Could be wrong, what do I know?

Bear in mind that in use, the loader is skimming the ground. You are not putting it in float and then extending and contracting it multiple times to the limits of its travel. So the amount of oil exchange is minimal. Also, as has been stated in this thread earlier, some of the oil is supplied by the opposing side of the cylinder. Pushing up on the loader could create a bit of air because the rod side of the cylinder will not provide enough oil to fill it. When the loader sinks, the opposite is true and excess oil is sent to tank. But the amount that it moves in the normal course of intended use is not so much and it recovers quickly when power is again applied.

Using four ports open in the float control instead of pump blocked (three ports open) would flood the circuit and keep it full at the expense of downstream functionality. Having the ability to trim the curl on a bucket while floating the loader is handy enough that it would make sense to use the less rigorous but fully functional scheme of blocking the pump port. Having the tank return line below the fill level in the tank would also prevent ingesting air into the system even with the blocked pump scheme.

 

[Industrial Toys]

It does make me wonder how the return oil enters the tank. The displacement of the one side of a cylinder is different from the other, so just allowing it to circulate from one side to the other wouldn't work, right? It might explain, why a poor mans floating top link I built didn't work very well. Just a cylinder filled with oil and the two ports connected via a valve. I tried a solenoid valve which didn't work and thought it was just the orfice size, but a high pressure ball valve didn't work either!

 

[beemerphile]

It does make me wonder how the return oil enters the tank. The displacement of the one side of a cylinder is different from the other, so just allowing it to circulate from one side to the other wouldn't work, right? It might explain, why a poor mans floating top link I built didn't work very well. Just a cylinder filled with oil and the two ports connected via a valve. I tried a solenoid valve which didn't work and thought it was just the orfice size, but a high pressure ball valve didn't work either!

Your poor man's system would have probably worked with an accumulator tank in the circuit. As far as where the oil enters the tank on a tractor, I'd like to know as well. I don't know much about tractor design, but with industrial hydraulics we always returned the oil below the tank level among other reasons to minimize aeration which could lead to cavitation. Cavitation leads to noise and dead pumps. I'm thinking that tractor hydraulics would have the same issues to contend with and would expect the oil to enter the tank below the fill level and as far from the pump suction as possible. You can't go by where the tank return line enters because it could have internal piping.

 

[Industrial Toys]

I guess I could have used two cylinders, one being turned around!

I am just trying to think about operating the bucket circuit on both my JD and Kubota loaders while the boom is in float. I'm almost thinking that something weird happens, meaning some interaction between the two circuits. Maybe I'm wrong.