Hold Me, Squeeze Me…Which, Or Both?

[Henro]

Sorry, but “Question about a grapple” was already taken as a thread title by PineRidge! /forums/images/graemlins/blush.gif

Anyway, in This Thread we tenderized the meat, so to speak, with respect to Junkman’s grapple hook up. No need to relive that here, but that thread does lead to my question.

I remember reports in the past of home built grapples being bent up (twisted, pretzeled) because the hydraulic cylinder that operated them pushed harder than the design could handle. I am almost certain the controls for those grapples were normal open-center control valves, plumbed up just like any auxiliary output would be.

We also have had some recent examples where electrically operated valves have been used to switch one of the spools of the loader valve, to operate the grapple when a button is pushed. Full hydraulic pressure would be applied to the grapple cylinder in this case also, and it would push quite hard, squeezing things between the grapple and the bucket pretty hard, until the control valve was centered, at which time the cylinder would lock in place.

The thread mentioned above gives an alternative-operating scheme for a grapple. At first it seems contrary to normal practice on a tractor’s open center hydraulic circuit, but once one takes a second look, it really is an alternative that could offer grapple movement, close and open, without having to worry about great pressure being developed by the grapple itself. The grapple would close and hold, and open and hold, and hold at any point between the two limits of travel, but would not damage itself, because the cylinder operating it could not in most cases develop enough force to do so.

So my question is, would it make a practical difference in operation, if the grapple were not able to squeeze real hard? If it could close down on something, then stay locked in that position, without being able to apply crushing force, would it matter much in a practical sense?

<font color="green"> [Quick summary of the how/why follows…]</font>

<font color="red"> (Background information, not part of the original question) </font>

The tractor in question has a closed center control valve hooked between the hydraulic line feeding the loader control valve, and the return to tank line. This control valve operates a cylinder which moves the grapple. Being closed center it has no effect on the system until it is operated.

It looks to me like the unless one of the open circuit loop valves are operated, the system pressure felt by the closed center valve would be quite low, maybe 100 PSI or less. Enough to operate the grapple, but not enough to apply crushing force.

The pressure available to the grapple cylinder would increase if one of the normal open-center-loop valves were operated, of course. And the grapple would squeeze harder if it were operated in conjunction with one of the open center loop valves.

 

[BigAl]

I don't think the grapple itself needs to "put the squeeze" on something until it breaks . Most of us use the grapple to pickup tree slash ,brush and so forth . I don't use my grapple to grab hold and try to pull something out of the ground . Usually I just want to pick up and hold an item in my bucket that without a grapple would be tough to do . So in answer to your question : NO, I do not think a grapple needs great crushing strenght . If it can grab it and hold it ,that is enough for me . I actually had this exact problem when I built my grapple and with the knowledgable help from TBN members was able to correct this ,by using a adjustable pressure relief valve .
Big Al

 

[rpeter]

The only thing I could think of is if you picked up something long and heavy (tree) and it was unbalanced (left to right). Not that it would be a good situation, but a pressurized grapple might be able to “hold on” rather than having the load twist.

 

[JimMorrissey]

Maybe somewhere in between makes sense. I like the idea of using a grapple to help extract large rocks / logs etc.....And you'd want something that will hold a large object tight into the back of the bucket. Dual cylinders with crushing force is likely not necessary (3000 psi), but a single smaller cylinder is probably what I'll look for.

The problem is finding the right design for a non-commercial CUT; one that is not too heavy or too light. I know a guy who bought a 800lb + one for a L48 and he is scared of it. It is too powerful and the machine would rock and sway with any kind of load up in the air (say loading a dumpster with high walls). He's selling it.

 

[Junkman]

</font><font color="blue" class="small">( It looks to me like the unless one of the open circuit loop valves are operated, the system pressure felt by the closed center valve would be quite low, maybe 100 PSI or less.)</font>

My basic question is "how do you know that this assumption of "100 PSI or less" is correct? /forums/images/graemlins/confused.gif I believe that one would have to know if the pump is a constant output pump or a variable output pump. Not knowing much about hydraulics..... actually knowing nothing, other than what I have gleaned out of the posts on TBN, I think that this would have to be determined before any qualifying statement be made. If I am wrong in my assumptions or statements, please correct me and let me know where I have gone astray. thanks Junk... starting 1st semester, hydraulics 101.

 

[KennyV]

Hello Henro…
With my grapple I am not able to break anything on it but I do like the fact that it will crush things to compact them. A lot of the things like brush and trees are more bulk than load. So if I am using my loader to transport I like that I can get a full bite and crush it and then bite more and maybe crush that and go for a third munch before I haul it off. So in that case you could not have too much crush …. But if that were a problem just reduce the diameter of your cylinder. That will increase your cyclic speed but reduce your crush. KennyV.

 

[Bowhunter]

Instead of looking for cylinders that exert no more than a set amount of psi, how about a different approach? How about something with adjustable pressure? The clamp trucks (modified forklifts with squeeze clamp front-ends) that we have at work use that principle. I haven't looked into how they work, but it seems workable if it isn't cost-prohibitive.

 

[quickervicar]

Bowhunter has the right idea. The cylinder approach will be tough to do right. The circuit approach would be easier, but expensive with manifold block, balance valves, etc. Possibly more expensive than the replacement cost of whatever it is that you're trying not to crush? /forums/images/graemlins/smirk.gif

 

[PineRidge]

Henro while I don't feel the need to put enough squeeze on a log to make toothpicks out of it, I do think that it's important to be able to travel with say a large log in the grapple and not need to worry about it bouncing out of the jaws or bucket.

That said I remember a conversation that Junk and I had on the telephone where he told me that he needed constant pressure on the control valve when traveling with a load so that it wasn't dropped.

So far I don't need to do that with the way my grapple is plumbed. I have picked up some heavy trees and moved to a pile before dumping without indication that I might lose them. And if you remember I was concerned when I was first thinking of building a grapple that I might need a double piloted check valve on the grapple cylinder to lock it in place.

While Junks grapple might open and close I still say it's not plumbed correctly to give himself full effectiveness of the grapple itself. It's his grapple he can use it as he sees fit.

 

[ronjhall]

<font color="blue"> Hold Me, Squeeze Me…Which, Or Both? </font>
Both
I have used my grapple to pull a log up to the bucket then hold it while I moved it to a new location.
The B2910/402 combination limits how much can be carried. I have moved a large log by dragging backwards with the bucket in float position with a large log held with the grapple.The valve used for Grapple is open center. I have had no problems with 2" cylinder coming open without check valves yet.
Build your grapple to take the loads that B2910 can be expected to apply to it. Does not need to be as strong as some I have seen on TBN. Including mine.