Double Pilot Operated Check Valve for 2 Cylinders???

[SkunkWerX]

Rob and Wayne County,

I understand both of your ideas regarding the synching of parallel cylinders, and I agree, when the cylinders are not under a load.
However, think of this and let me know if you agree with me?

The tiller weighs approx. 550#

While it is in the air, transported on the 3PH, let's just say there is no resistance, it may even be negative, due to the weight of the skids pulling down on the cylinders.

However, as soon as you set it on the ground, in working position, there will be 550# worth of tiller spread across the 2 cylinders. Given this load, and the cylinders connected in parallel, shouldn't they both seek the same pressure, thus, causing each of them to be extended equal lengths?
(Versus go crazy-unbalanced and have one side at 9" and the other at 0")

I guess what I am postulating, is that the weight of the tiller itself would act as the "tension spring" ??? When it's in transport, it wouldn't matter, and once height is adjusted, the DPOV is going to keep it there?

Does this make any sense? Am I missing a dynamic that would cause the cylinders to go out of whack?

Just like dual cylinder grapples, piped in parallel, one will close, until it meets resistance, then the other will "catch-up" until it meets the same or similar resistance. From that point forward pressure and force are equal in both cylinders. It is only when they are NOT under any substantial load that one moves farther/faster than the other?? Right?

Just throwing out the other side of the coin, to see what you guys think.

 

[3RRL]

The flow control valves would have plenty of adjustment to compensate for the changing physical characteristics of a wearing cylinder. They take a minor amount of playing with to get them set, but the guys I know with them use them quite frequently and rarely have to adjust them.

The spring loaded plungers you describe would work the same as an external spring, might even be a "cleaner" setup. Whatever way you provide the resistance, you are trying to load both cylinders equally so that they travel equally. Lets say you have two sister cylinders. One takes 50 lbs to move it, the other 55 lbs. If you used a 10 lb. spring, it would be plenty of pressure to overcome the internal differences. All you are trying to do is overcome the differences, not the total load.

Hi Wayne,
I agree with what you have said here, (I know it's not total load) that the spring or the plunger/detent set up would allow a "range" or "window" of different resistance to occur and still work. Such as if one side galled up or got sand in it and started to bind up. In your example of 10lb spring, there would be a 10lb window or range that the resistance can be off and they would still synchronize. But if the sand or binding or galling causes it to exceed the 10 lbs, they would not. So because we don't know "how much" the galling or binding "might be" (if any), we need to provide a larger window for them to synchronize.

The flow control valves would have plenty of adjustment to compensate for the changing physical characteristics of a wearing cylinder. They take a minor amount of playing with to get them set, but the guys I know with them use them quite frequently and rarely have to adjust them.

This however for (our example) I'm still unclear about, so maybe you can help me understand?
I understand there is adjustment to get them synchronized, but my question would be after that adjustment, what kind of window do they have if one encounters dirt or galling or binding? If they are set at let's say 50 and 55 lbs to synchronize, how would they react if one started to bind up like from dirt getting in the linkage? It would need to be re-adjusted, right? That's what I want to know. Is there a window like on the springs?
Perhaps that kind of set up would be great if you knew the resistance would never change, like in a controlled environment. But maybe not so good for applications where the environment changes due to dirt or binding like what could happen in Skunk's case? I dunno, that's why I'm asking.

However, as soon as you set it on the ground, in working position, there will be 550# worth of tiller spread across the 2 cylinders. Given this load, and the cylinders connected in parallel, shouldn't they both seek the same pressure, thus, causing each of them to be extended equal lengths?
(Versus go crazy-unbalanced and have one side at 9" and the other at 0")

I guess what I am postulating, is that the weight of the tiller itself would act as the "tension spring" ??? When it's in transport, it wouldn't matter, and once height is adjusted, the DPOV is going to keep it there?

That is a good question.
How do you know the 550lbs will be spread evenly? What if the skids are resting on a dip or bump? Would the weight still be spread out exactly evenly between the two? That's why I suggested the vehicle (springs or spring loaded plunger/detent) to accommodate for variances in load imposed on each one. To give the cylinders a window to operate and synchronize successfully.
LOL ... of course I could be wrong (probably am) but just thought to bring up that instance?

 

[SkunkWerX]

That is a good question.
How do you know the 550lbs will be spread evenly? What if the skids are resting on a dip or bump? Would the weight still be spread out exactly evenly between the two? That's why I suggested the vehicle (springs or spring loaded plunger/detent) to accommodate for variances in load imposed on each one. To give the cylinders a window to operate and synchronize successfully.
LOL ... of course I could be wrong (probably am) but just thought to bring up that instance?[/QUOTE]

- - - - -

Rob, I actually thought about that, after I wrote my hypothesis.

For one, the Tillers gear box is on one side, therefor that side will carry a greater load. So, I thought to myself, OK, would I need to balance the tiller's weight, side to side??
I don't know how much of a weight variation would be needed to affect, let's say, a couple of 2 inch cylinders.

Let's look at a plausible scenario: ( and trust me, I don't know the answer, can only guess...)
If we placed a 50 lb. weight on one end of the tiller, would we expect the corresponding cylinder, on the now weighted end, to sag? If it was pnuematic, at 30 psi, like a tire, then Yes, it would compress somewhat because air readily compresses. But since it's hydraulic fluid, at, let's be conservative, at a modest 1000 psi, then how much variance in weight, between the two cylinders, would it take to make one or the other noticeably depress lower than it's parallel cylinder?

I am guessing it would take quite a bit of force to "dip" one of the cylinders noticeably over the other. But it's just that...a guess.

My gut tells me, Hydraulic fluid, that is already pressurized, is not going to give in to 50# or 100#, or a bit of uneven ground. The force of the fluid pressing on the internals of the cylinder far exceeds the external force of some weight placed at one end of the tiller.
Maybe if two of us jumped up and down on one end of the tiller, we could get it to move, but I don't know if the reasonable forces that will be exerted on the cylinders, during usage, will even begin to approach the point where one of the cylinders would sag, vice the other?

But, I put all this forth as questions, and guesses, for discussion, and even for dispute, because I am not 100% sure. Just a hunch.

 

[3RRL]

Skunk,
I was thinking more in terms of when you go to adjust the cylinders, not when they are already extended. I don't think you could budge them, like you say, once they are out there already. But when you go to adjust them down more, and the weight of the tiller is on the skids, the lighter side of the tiller will move up, or more correctly, that side's skid will move down before the heavier side. And visa versa, when sucking them up, the heavier side will suck up before the lighter side.

I am going with the premise that you were going to adjust the cylinders when it was on the ground....That's what I was thinking?
And again, I don't know for sure either. It would be cool for you to make them without the detents first, since they can be added later. Then test it and maybe it will work just fine? I love this thread because I'm getting a tiller pretty soon and would like to do what you are contemplating. I like your idea a lot, and none of my hair brained projects have needed to have synchronized cylinders.

 

[Wayne County Hose]

This however for (our example) I'm still unclear about, so maybe you can help me understand?
I understand there is adjustment to get them synchronized, but my question would be after that adjustment, what kind of window do they have if one encounters dirt or galling or binding? If they are set at let's say 50 and 55 lbs to synchronize, how would they react if one started to bind up like from dirt getting in the linkage? It would need to be re-adjusted, right? That's what I want to know. Is there a window like on the springs?
Perhaps that kind of set up would be great if you knew the resistance would never change, like in a controlled environment. But maybe not so good for applications where the environment changes due to dirt or binding like what could happen in Skunk's case? I dunno, that's why I'm asking.

Regarding the flow controls, mechanical binding or any other outside force on the cylinder, has no effect on the fluid flow. The only thing flow control valves know is flow. They meter the amount of fluid entering and exiting the cylinder. 10 gpm at 100 psi is the same volume of oil as 10 gpm at 2500psi. And that's what we're trying to control here is the volume of oil as the volume controls the cylinder's position.

I can see outside forces changing things when using springs, but there isn't a much dirtier, dustier environment than these stone cutting yards and they have not had a problem with the spring setup yet.

 

[Wayne County Hose]

That is a good question.
How do you know the 550lbs will be spread evenly? What if the skids are resting on a dip or bump? Would the weight still be spread out exactly even.

My gut tells me, Hydraulic fluid, that is already pressurized, is not going to give in to 50# or 100#, or a bit of uneven ground. The force of the fluid pressing on the internals of the cylinder far exceeds the external force of some weight placed at one end of the tiller.
Maybe if two of us jumped up and down on one end of the tiller, we could get it to move, but I don't know if the reasonable forces that will be exerted on the cylinders, during usage, will even begin to approach the point where one of the cylinders would sag, vice the other?

But, I put all this forth as questions, and guesses, for discussion, and even for dispute, because I am not 100% sure. Just a hunch.

You guys are thinking a single acting cylinder, like on a snow plow angle setup. When you use double acting cylinders, they will not "even out" or change position based on any load. When the cylinder is extended half way, there is a certain volume of oil in both halves that remains constant. If you change the position of the rod, you are changing the total volume of the cylinder because you have more or less rod inside the cylinder. Therefore, irregardless of load, the cylinders will not "even out" as single acting cylinders would. In order to move oil in a parallel double acting cylinder configuration, you change the total volume of oil in the cylinders therefore requiring oil either from or to tank.

 

[SkunkWerX]

Skunk,
I was thinking more in terms of when you go to adjust the cylinders, not when they are already extended. I don't think you could budge them, like you say, once they are out there already. But when you go to adjust them down more, and the weight of the tiller is on the skids, the lighter side of the tiller will move up, or more correctly, that side's skid will move down before the heavier side. And visa versa, when sucking them up, the heavier side will suck up before the lighter side.

I am going with the premise that you were going to adjust the cylinders when it was on the ground....That's what I was thinking?
And again, I don't know for sure either. It would be cool for you to make them without the detents first, since they can be added later. Then test it and maybe it will work just fine? I love this thread because I'm getting a tiller pretty soon and would like to do what you are contemplating. I like your idea a lot, and none of my hair brained projects have needed to have synchronized cylinders.

Rob, (and Wayne County),

Thanks for the continued thoughts, this is a very good discussion.

Rob I do see what you are saying, and that's how this whole discussion got started, because that was my concern.

Let me offer another side of the coin, again.

Q: How much weight or external pressure/force would it take to compress a 2" cylinder at 1000psi? Let's just say we aren't going to be able to budge it by hand, or even by standing on it, just like a bottle jack, it will be rigid.

If it takes XXX force to compress a 2" cylinder a total of 1" , then, wouldn't it also still take that much force to compress it even if it were plumbed in parallel with another 2" cylinder?

I guess my thinking is this: If wer were using wimpy small 3/4" bore cylinders, then the threshold to compress them with outside forces would be much more "likely" to happen, than when we use much larger cylinders that take force beyond what we reasonably expect in our application.

Simply put: If KingKong stepped on one side of the tiller, then yes, that side is going to compress, but in the same example, if we have a 120 lb. boy step on one side of the tiller, would the downward force he exerted be anywhere near the force needed compress the cylinder even a 1/4" ????

I am theorizing that a pair of 2" cylinders are grossly overkill for this application, however, that fact will give them the strength not to compress due to some extra weight on one side, or a bump in the ground. There must be a threshold for comprssion?
I am theorizing THAT threshold is the amount of force it would take to overcome the pressuirized cylinder??

OK, so, if that is the case, it's a pretty easy build.

If, in fact, they do have problems balancing, then my thought would be coil-over compression spring, like on a Shock absorber or a MacPherson strut.
That may be costly, so, the obvious alternative would be standard "stretch" springs, holding the cylinders back a bit.

But, as I pondered what the springs are doing, aren't they simply exerting additional force in an attempt to keep the cylinders in balance? Wouldn't the weight of the tiller be accomplishing the same thing?

I'm having a circular disuccsion with myself...this is great!

Thanks guys, for the thoughts and suggestions. Worse case scenario, we'll bolt on a pair of cylinders, and start taking readings and deflection measurments.

 

[MJPetersen]

Well you generated some educational discussion!! A simple sounding approach suddenly sounds a whole bunch more complicated. I am back to thinking about a single shaft the width of the tiller placed just above and behind the rear box tube that forms the top frame. You could mount the cylinder out on the far right (non drive) side and have a simple linkage extending to the skid shoes. That is my opinion only.

No springs, detents, flow dividers, extra plumbing and hoses, cleaner and narrower width and simpler construction--IMO. Do let us know what and how you do it.

Mike

 

[SkunkWerX]

Well you generated some educational discussion!! A simple sounding approach suddenly sounds a whole bunch more complicated. I am back to thinking about a single shaft the width of the tiller placed just above and behind the rear box tube that forms the top frame. You could mount the cylinder out on the far right (non drive) side and have a simple linkage extending to the skid shoes. That is my opinion only.

No springs, detents, flow dividers, extra plumbing and hoses, cleaner and narrower width and simpler construction--IMO. Do let us know what and how you do it.

Mike

Mike,

You are observant, the right side of the tiller does have space for a cylinder, and it is about the only place free of clutter. If i use the single cylinder it will certainly be with your idea of the rotating shaft and linkages.

I'm going to go down both paths a ways, single cylinder on top, as well as double cylinders each side, until i come to a final verdict.

I may have another project falling in my lap in the next week, so this one may go in 2nd place....more on that in the Build It Yourself section, should everything fall into place on this other project.

 

[3RRL]

Hi Skunk,
I am interested in whichever way you choose to go. It will be informative for sure.
But I still have a question for Wayne if you don't mind, since (dumb me) I am not clear about what he said regarding my question about using the flow control valve system.

Regarding the flow controls, mechanical binding or any other outside force on the cylinder, has no effect on the fluid flow. The only thing flow control valves know is flow. They meter the amount of fluid entering and exiting the cylinder. 10 gpm at 100 psi is the same volume of oil as 10 gpm at 2500psi. And that's what we're trying to control here is the volume of oil as the volume controls the cylinder's position.

So let me ask you again Wayne.
If two cylinders are set up in parallel like Skunk was wanting,
using the flow controls,
after they are synchronized with no load on them,
they will move the same amount together regardless if you pinch one of the rods shut, so it will not move or would be much harder to move than when it was free (like it was jammed).
Is that what you are saying?