Question about "float" position

[MossRoad]

I'm pretty sure my return is at the lower side of the tank, not the top, to avoid foaming, but I'd have to do a visual inspection the next time I am out in the garage.

And yes, I agree that the two sides cannot contain the same volume of fluid due to the space taken up by the rod on one side of the piston. That's why the push is stronger than the pull on a hydraulic cylinder. The surface area of the piston is less for the side that the rod attaches to.

 

[J_J]

To all.

When a float circuit is activated, it connects the ports of the hydraulic cylinder together, allowing it to retract under the weight of the boom or arm. The fluid displaced from the piston side of the cylinder is directed with priority to the rod side , before any excess volume is returned to the hydraulic reservoir. An orfice controls the speed with which the hydraulic cylinder retracts.

 

[J_J]

There is fluid on both sides of the piston at all times. You can not afford to be sucking air into a hydraulic circuit, because you run the risk of the diesel effect, which is, if enough air/oxygen gets in the cylinder, and then it is compressed, it can explode, and destroy the cyliinder.

 

[SPYDERLK]

I'm pretty sure my return is at the lower side of the tank, not the top, to avoid foaming, but I'd have to do a visual inspection the next time I am out in the garage.

And yes, I agree that the two sides cannot contain the same volume of fluid due to the space taken up by the rod on one side of the piston. That's why the push is stronger than the pull on a hydraulic cylinder. The surface area of the piston is less for the side that the rod attaches to.

Yes, I agree with this rationale -- maybe. Consider fluid being returned to the tank with entrained air. Wouldnt it be better to introduce this return gently, over a broad area, near the surface to both prevent jetting air into the oil and introducing incidental entrained air too close to the suction pickup?
Conjecture.
Larry

 

[J_J]

Where is this air coming from that some of you are suggesting that it is being sucked in from somewhere. This only happens rarely and should be avoided. This can occur when the piston is being pushed back faster than the fluid can enter. Most systems are designed so as to not suck air, from the tank, by placing the suction ports about midway in the tank. You don't want them on the bottom, as they might suck up some crud on the bottom of the tank. If you have any air in your system, it could be caused by cavitating fluid, which occures when you have reached the vapor barrier of the fluid. You should not let a hydraulic system cavitate for very long. This is not good for the system, mainly the pumps and motors.

 

[MossRoad]

I just went out and opened the hood on my PT425 and observed the hydraulic tank. ALL hydraulic hose connections are set 2-3 inches from the bottom of the reservoir, about 12" lower than the top of the tank and at least 10" under the fill level on the dipstick. With the one exception being the suction port for the filter that goes to the variable volume pump. That port is only an inch from the top of the tank! So, my best guess is that there is a pickup tube on the inside of the tank for that and it is only located up high to accomodate the hydraulic filter.

 

[MossRoad]

Also, ALL hydraulic hose connections are on the lower, left side of the tank except for the pickup for the variable volume pump, which is on the upper right side of the tank, far from any of the other ports. Don't know if this is by design or simplicity.

 

[KentT]

Where is this air coming from that some of you are suggesting that it is being sucked in from somewhere.

Dunno, JJ, it must be Phlogiston instead of normal air, since it's coming from "nowhere"...

Phlogiston theory - Wikipedia, the free encyclopedia

 

[RegL]

What was the question again?

 

[MossRoad]

What was the question again?

When you put the 425 in the float position, what floats?

 

[MossRoad]

Dunno, JJ, it must be Phlogiston instead of normal air, since it's coming from "nowhere"...

Phlogiston theory - Wikipedia, the free encyclopedia

Oh, my! Now THAT is a theory! Great reading. When did you first hear of it? Just curious.

 

[MossRoad]

Watch this video of my PT425 mowing. The FEL is in float. Half way through the video, I climb up a small, 12" berm. It isn't real clear, but you can see how no wheels on the mower deck, or the tractor, leave the ground.

 

[KentT]

Oh, my! Now THAT is a theory! Great reading. When did you first hear of it? Just curious.

Some chemistry course I had back in the days when that theory was still believed -- or shortly thereafter...

Seriously, I don't remember other than it and the concept of outer space being filled with "ether" were both long-believed but subsequently de-bunked scientific theories...

I just wish I could understand what Steven Hawking or Einstein were saying -- to heck with debunking them...

 

[J_J]

Dunno, JJ, it must be Phlogiston instead of normal air, since it's coming from "nowhere"...

Phlogiston theory - Wikipedia, the free encyclopedia

Sometimes, it is hard to tell if one is being mocked, or supported. My point was, if there is air in the cylinder, you have a problem.

 

[KentT]

Sometimes, it is hard to tell if one is being mocked, or supported. My point was, if there is air in the cylinder, you have a problem.

JJ -- I was supporting you 110%... and jesting about those who keep saying that there's something on the other side of the piston other than fluid...

Except for bubbles caused by shear and cavitation in motors and pumps primarily, (and a bad thing, and something to be minimized and dealt with), the circuits should have nothing but fluid in them...

 

[MossRoad]

Sometimes, it is hard to tell if one is being mocked, or supported. My point was, if there is air in the cylinder, you have a problem.

As Kent said, I agree with you completely. If air is getting behind one side of the piston in the cylinder, there is a problem.