single action cylinder question(s)

[blenderbender]

I picked up a Chinese sickle bar mower that has a single action hydraulic cylinder, power up/gravity down. My Kubota tractor has a single set of rear remotes on a dual action control. I don't understand hydraulics nearly well enough, but I'm guessing this is a problem in terms of using this single action cylinder and I don't have a clue what my options might be other than swapping out for a dual acting cylinder. Any thoughts appreciated!

 

[oldnslo]

Does your tractor have “float” option on the rear remotes? If yes you can use that feature or if not just plug the one hose into one of the quick disconnects. Pull back to raise, push forward to lower same as double acting. Yes lowering you will be at system relief for a few seconds but once you release the lever it will be ok.

 

[ptsg]

When lowering, being a dual acting valve, it will push fluid through the relief at max pressure on the non used port, which is usually bad if done for long periods of time. For a short run like this? It's perfectly fine.

 

[blenderbender]

I guess I can't say if it has a float option on the rear remotes. All I've ever used it for is to adjust the angle on back blade when plowing snow. The lever floats in the center position but I don't think that's what you mean.

 

[blenderbender]

When lowering, being a dual acting valve, it will push fluid through the relief at max pressure on the non used port, which is usually bad if done for long periods of time. For a short run like this? It's perfectly fine.

I'm not certain what you mean by "short run". Thanks!

 

[ptsg]

I'm not certain what you mean by "short run". Thanks!

I meant for a short time. Like lowering the sickle bar. Only a couple seconds, then the valve is back to neutral.

 

[blenderbender]

So, I'm guessing it doesn't matter which port I plug into, but that will determine if I push or pull the lever to lift the sickle bar?

 

[ptsg]

So, I'm guessing it doesn't matter which port I plug into, but that will determine if I push or pull the lever to lift the sickle bar?

Yes. That's it.

 

[CobyRupert]

So, I'm guessing it doesn't matter which port I plug into, but that will determine if I push or pull the lever to lift the sickle bar?

Yes. Basically. When the lever is at neutral position, in the middle, the cylinder isn’t moving, in or out.

To find out if you have a “float position” on the SCV, press the lever all the ways forward (or backwards) and see if it can “pop” forward just a little more to a detent position and stay there. This is another type of “neutral position”, where the cylinder can float in or out, without resistance, if the sickle bar is manually raised or lowered (or is following the contours of the ground) (i.e. “float”).

Gravity will lower the sickle bar to its lowered position when the lever is in float position. Knowing this, you should connect the hydraulic hose to the specific port such that moving the lever lowers the bar just before the lever hits the detent float position. Follow?

You don’t want to press the lever and have it raise raise the bar, then move lever more to the float detent position and the bar drops from some height.

Realistically, it’s not a big difference, but pushing the lever in one direction, shouldn’t have two outcomes (raise and then drop/float).

 

[dicktill]

Does your tractor have “float” option on the rear remotes? If yes you can use that feature or if not just plug the one hose into one of the quick disconnects. Pull back to raise, push forward to lower same as double acting. Yes lowering you will be at system relief for a few seconds but once you release the lever it will be ok.

When lowering, being a dual acting valve, it will push fluid through the relief at max pressure on the non used port, which is usually bad if done for long periods of time. For a short run like this? It's perfectly fine.

Interesting! Can this limitation be "corrected" by running an extra line from the "non-used port (coupler)" back to the tank?

TIA, Dick

 

[ptsg]

Interesting! Can this limitation be "corrected" by running an extra line from the "non-used port (coupler)" back to the tank?

TIA, Dick

Sure can. That's indeed one way to do it. A lot of valves, have a little lever that will do just that but internally.

You can also put a Tee fitting between the quick disconnect and valve, then a shutoff valve and a hose back to the tank. That way, it's always set up and ready to go.

 

[grsthegreat]

On single cylinder hydraulics, there should always be a hose run back to the tractor fill port. I was told not to just leave 1 hose unhooked. What Kioti did was have me add a connector to the hydraulic fill port on my tractor, than the second drain line went there. It still uses only 1 of the standard rear remotes. In my case it was power down rear post hole digger and float when PHD was raised. This port is the same thing they add if i was to install a backhoe.

 

[LouNY]

Unfortunately very few of the smaller tractors have a float option for any of the rear remotes.
One way to get it would be to use the loader joystick control as most of those do have a float position. A diverter valve could be plumbed into the loader circuit to use the loader lift/lower and float.

Most single action cylinders will only have one hose. The other end of the cylinder is normally just vented to atmosphere.

 

[grsthegreat]

Unfortunately very few of the smaller tractors have a float option for any of the rear remotes.
One way to get it would be to use the loader joystick control as most of those do have a float position. A diverter valve could be plumbed into the loader circuit to use the loader lift/lower and float.

Most single action cylinders will only have one hose. The other end of the cylinder is normally just vented to atmosphere.

the cylinder itself has 1 hose, but theres a diverter box before the cylinder with 3 connection points. (on mine)

 

[ptsg]

the cylinder itself has 1 hose, but theres a diverter box before the cylinder with 3 connection points. (on mine)

View attachment 2804218

View attachment 2804219

That's a relief valve so the cylinder doesn't apply too much force and break stuff. The other hose coming from it, it's just the excess pressure going back to the transmission.

 

[KennyG]

I don't think there's anything to be concerned about here. My mid mount mower has a single acting lift cylinder with one hose. I attach it to the curl up loader port. To lower it I just push it in the down direction. It doesn't need to go into float.

 

[kennyd]

This is exactly what the PRV (pressure relief valve) is for, no issues whatsoever.

 

[Cycledude]

What are you planning to use the sickle mower for ?

 

[CobyRupert]

Interesting! Can this limitation be "corrected" by running an extra line from the "non-used port (coupler)" back to the tank?

TIA, Dick

You mean have a loose line with an open end that gets stuffed back into the hydraulic fill port?

Hmmm…well sure, that would prevent the relief valve operating for a few seconds when lowering / retracting the cylinder, but wouldn’t you the have ~3000psi of hydraulic fluid dumping out the end of an open hose?

I don’t know, is the GPM low enough, even if the pressure is high, that this isn’t scary or dangerous? Or is the pressure low as long as it doesn’t meet resistance? IDK.

 

[ptsg]

You mean have a loose line with an open end that gets stuffed back into the hydraulic fill port?

Hmmm…well sure, that would prevent the relief valve operating for a few seconds when lowering / retracting the cylinder, but wouldn’t you the have ~3000psi of hydraulic fluid dumping out the end of an open hose?

I wouldn’t want to be any where near it, even if I did anchor the end of the hose. I don’t know, is the GPM is low enough, even if the pressure is high, that this isn’t scary or dangerous? Or is the pressure low as long as it doesn’t meet resistance? IDK.

It's free flow going back to the tank. If there is no resistance in the flow path, there is no pressure.

Either way, I'm sure dicktill would do something more civilized than just shoving an hose through the fill port and having the fill port open to the elements.