Question about "float" position

[ddonnell]

When you put the 425 in the float position, what floats? Is it the loader arm assembly or the tilt/curl of the attachment plate, or both. And how much resistance to "floating" from the hydraulic cylinders is there. The reason I ask is that I am trying to conjure a way to use a 2" male receiver tube mounted to the drawbar of my broadcast spreader to hook into a receiver on the front of the PT. The rigidity of this setup could be a problem with the spreader frame, axle, and wheels without some "give or pivoting" somewhere in the hookup. Do you think the PT's float position would allow for enough flexing to follow uneven ground contours or would I need some sort of hinging hitch scenario?

I'm actively pursuing the sale my SCUT setup, but in the meantime I am thinking of possible ways to use some other existing equipment on the PT. Found some used forks today to fab into an adjustable setup for either my present loader or, hopefully, future PT.

 

[KentT]

The float is on the control for the lift arms... not the tilt/curl. It allows the front-mounted implement such as a moving deck to move up and down, following the contours of the ground...

I've found it works pretty well for heavy attachments, but not necessarily for light ones. It takes a certain amount of weight or force, it seems, to push the hydraulic fluid from one side of the lift cylinders back through the circuit to the other side...

It's not quite the same as something hanging freely from a chain, like a mowing deck on a garden tractor for example, and rising and falling as it follows the ground. In addition to pushing the fluid through the circuit from one side of the lift cylinders to the other, in float position it must also lift the weight of the fairly heavy lift arms themselves....

 

[MadReferee]

Float is a function of the control valve. Both spool work ports are internally redirected so that their fluid is exhausted to the tank/sump. This allows gravity to control the loader lift/lower cylinders causing the whole assembly to "float" over the ground. Fluid is not moved from one side of the cylinder to the other, rather it is exhausted.

 

[KentT]

Float is a function of the control valve. Both spool work ports are internally redirected so that their fluid is exhausted to the tank/sump. This allows gravity to control the loader lift/lower cylinders causing the whole assembly to "float" over the ground. Fluid is not moved from one side of the cylinder to the other, rather it is exhausted.

My poor terminology, I guess. The fluid volume on one side of the piston in the cylinder/ram must increase while it is decreasing on the other side, otherwise it would be hydraulically locked. Fluid is moving in the system, essentially from one side of the circuit to the other. While it may literally go back to the tank when it is exhausted, on the other side of the piston it must pull fluid from the tank in order for the piston to move...

Plus, the resistance to that piston moving feels somewhat akin to a shock absorber, which essentially functions the same way... there is resistance to the piston moving, which is the point I was trying to make. It is not simply a matter of the implement moving up and down freely... there's resistance to the implement moving up, and there's also resistance coming down -- which is overcome by the weight of the implement and the lift arms. But, the movement is not as quick, nor as direct as if it were hanging freely from a chain...

 

[MadReferee]

Both work ports are connected to the tank/sump when the spool is in float. This means both ends of the cylinder are connected to tank. Any fluid in the cylinders will be exhausted because it will take the path of least resistance. It's just like disconnecting the hoses from the cylinders. Gravity will force the loader down (because the cylinders are open to tank) which causes the fluid in the cylinders to exhaust to tank. There is no hydraulic locking since there is no pressure in the spool's work port circuit.

Because both ends of the cylinders are open to tank the whole loader "floats". Since there is no pressure either up or down other than the weight of the loader itself, the loader will follow the contour of whatever it is resting on, ie. the ground.

You must be thinking of regeneration which is what most valve spools have that are used for bucket curl/dump. Regen prevents the floppy bucket syndrome by redirecting exhaust fluid back to the pressure side of the dump cylinder. Because gravity can cause the bucket to dump faster than the fluid can fill the cylinder, the regen compensates for that.

 

[KentT]

Mad,

I don't disagree with a thing you're saying -- except I continue to make the point that the double-action cylinders feel like a "shock absorber" when in the float position, since any movement of the piston requires fluid to move in two directions -- one side of the piston pushes fluid out, while the piston pulls fluid into the other side... it must do so, or the piston would not move.

Try pulling a piston out with your hands, when it is connected to hydraulic lines and they are full of fluid -- you'll see what I mean. Those pistons act like a shock absorber. (BTW -- it's not exactly like disconnecting lines -- because when you disconnect the lines, the piston can pull air into the sytem on whichever side is needed to allow movement -- when it is connected it must pull fluid. Disconnecting the lines will bleed fluid off the high-pressure side, while pulling air -- not fluid -- into the low-pressure side.)

The point that I'm trying to make is that an implement on the front of a PT doesn't move up as readily as it would otherwise, since it must overcome the shock action of the cylinders AND lift the heavy lift arms of the PT...

The weight of the implement and lift arms brings it down pretty readily in float position, but it doesn't move up nearly as readily. This isn't very noticable with buckets, which are closer to the lift arms -- but it is quite noticeable when using a rough-cut mower or some other wheeled implement that sticks way out front (I also have a landscape rake with guide wheels in front). It is quite easy to push the front tires off the caster wheels when you come to an upslope and are turning simultaneously, for example...

Been there, done that! It's a pretty common problem, and the factory now offers solid tires on the guide wheels because of that.

 

[MadReferee]

The bottom line is that when the spool is in float each work port is connected to the tank/sump. Fluid cannot go from one side of the cylinder to the other, it can only go out to the tank. Being open to the tank there is no pressure on either side the cylinder. Gravity forces the loader down which causes the fluid to exhaust back to tank since it's the only place it can go. The loader is now resting on the ground with no hydraulic pressure on either side of the cylinders and the cylinders are effectively free to move in either direction.

I agree with your statement that while in float the only resistance to movement will be the geometry of the loader design, the weight of the loader itself, the tightness of the loader pivot pins and the close (or loose) tolerances of the components inside the cylinders. However, fluid has already left each side of the cylinders so it has no bearing on how hard it might be to move the cylinders in either direction.

 

[KentT]

However, fluid has already left each side of the cylinders so it has no bearing on how hard it might be to move the cylinders in either direction.

Simply not true... what is in those cylinders, on each side of the piston, if not fluid? It may not be under pressure, but there is fluid there -- not air or vacuum...

And when the front implement moves up or down, those pistons act like piston-type pumps, pumping fluid back to the tank on one side of the circuit, and pulling fluid back from the tank on the other...

The hoses back to the tank provide resistance to the fluid movement in both directions, hence the "shock-like action." I agree that the pressure equalizes back to zero, but momentarily there is pressure when the front implement moves up or down...

Try pulling (or pushing) a cylinder in an open-center circuit and you'll see what I mean. There's resistance to movement... The weight of implements (and lift arms) easily overcome this on the downstroke, but the implement will move slower (at least initially) in the upstroke than it would if no cylinder was involved.

 

[MadReferee]

Simply not true... what is in those cylinders, on each side of the piston, if not fluid? It may not be under pressure, but there is fluid there -- not air or vacuum...

There is no fluid there. There is no way for any to get there. Are you sure you understand how a spool valve in float works? I am wondering.

And when the front implement moves up or down, those pistons act like piston-type pumps, pumping fluid back to the tank on one side of the circuit, and pulling fluid back from the tank on the other...

Nope. Even if it were possible, there is no way near enough suction pressure to suck any fluid back from the tank.

The hoses back to the tank provide resistance to the fluid movement in both directions, hence the "shock-like action."

Huh?

I agree that the pressure equalizes back to zero, but momentarily there is pressure when the front implement moves up or down...

There is always some pressure but in this case it is so small that it is insignificant.

Try pulling (or pushing) a cylinder in an open-center circuit and you'll see what I mean. There's resistance to movement... The weight of implements (and lift arms) easily overcome this on the downstroke, but the implement will move slower (at least initially) in the upstroke than it would if no cylinder was involved.

What does an open center circuit have to do with this at all? We are talking a work port circuit here. Your comments obviously show that you are not understanding what is happening in float.

 

[ddonnell]

Assuming there would be no buffering effect of the cylinders (I think there would be some) do you think that the "dead weight" of the lift arms would be too much on the "beefed up" tubular frame of a "typical" 200# capacity tow-behind broadcast spreader (12" pneumatic tires)? My idea would be to extend and crossbrace the 2" receiver tubing back near hopper of the spreader to take torque off the thinner tubular frame of the spreader.

If too much weight, my second thought would be some sort of hinge in the male receiver tube that would allow maybe 4-5" of vertical play of the spreader with the loader arms held at a midpoint of the hinge travel. I assume that the loader arms stay pretty much where you set them when the hydraulics are pumping. Thoughts anyone?