Question about a grapple

[Henro]

I have no experience with a grapple (yet /forums/images/graemlins/smile.gif ) but do have a couple thoughts...

Since it was pointed out above that whatever the grapple is pushing against will likely compress anyway (unless it is concrete), it seems that nothing would be gained by using a pilot-operated check valve setup. Also time is another consideration. How long is the grapple likely going to be expected to hold whatever it is holding? Probably a couple minutes while moving from the pickup point to the dump point. So there is not a lot of time for the system to leak down.

Now for comparison, a tilt cylinder when brush hogging might be asked to hold position for hours at a time. In this case, it has been reported by some here that their tilt cylinder drooped an inch or so, in an hour, and required adjustment to keep the cut level. An inch at the cylinder is double that across the mower deck. A check valve that would lock the cylinder in postion in that case would be very useful.

So let me throw something out that I have not seen mentioned before. How about an accumulator on the clamp side of the grapple cylinder? Such as:

One of these, maybe?

A 1 quart would be more than enough, at least that is my guess. The accumulator would hold pressure on the close side of the cylinder, and keep it tight, so to speak, as the cylinder would keep pushing against the "load" which is the stuff the grapple is clamped against.

I suppose using an accumulator would introduce some delay in the unclamp operation, since the accumulator would have to be "drained of pressure" to some degree before the grapple started to open. I doubt it would take very long though for a quart of fluid to move...

Now this is just a WAT (Wild A**ed Thought) but I bet it would work. IF keeping pressure on the grapple is important in one's application.

Myself, I when I get around to building a light duty grapple for my loader, I will just use a simple control valve (or the loader hydraulics and a electric operated diverter) and will only worry about getting more exotic when something teaches me that I need to.

Note of warning: If anyone would use an accumulator, you MUST keep in mind that it is an energy storage device, and can hold pressure when the tractor is turned off, and would probably have enough pressure/flow available to stroke the grapple and cause in the worst case great harm. Not sure how this might happen if it is on the close side of the cylinder, but energy is energy...must always be respected.

But like I said, I doubt check valves, accumulators or anything else exotic is needed for most of us when it comes to grapples...

 

[stevenf]

ACMAN I hadn't considered that but I think your right I'm moving brush a 1/4 mile or so at times and during the transport I have to tighten up my grip several times to keep from loosing my load with the bucket curled. I've included a photo of mine grapple sorry its not loaded up with stuff as I was heading out when my honey snapped the picture.
Steve

 

[PineRidge]

Looks like it's a split decision on the check valve. Even some of you whom own grapples don't believe that the check valve would be of any benefit to a grapple.

Bill I'm not sure what function a hydraulic accumulator would have with a grapple application. The only accumulators that I'm familiar with are the ones used in refrigeration or air conditioning. In that case they prevented liquid refrigerant from returning to a compressor and slugging the valves.

I'm going to think about this for a bit. I still might be apt to add a check valve to a grapple just to see for myself if it has some advantages. Guess I need to justify spending the extra hundred bucks in my mind beforehand. Who knows we may all learn something from the experiment if I do install one.

 

[Henro]

PineRidge,

Just had a thought...

You are going to use that solenoid diverter valve for your grapple, right? So you can use the loader control to work the grapple...I assume anyway.

What I wonder is: Wouldn't the diverter function as a lock valve when it was switched to the normal position. I mean, wouldn't both hoses coming from the grapple cylinder be essentially close ended by the diverter when the diverter was de-energized?

So it kind of looks like if you are using a diverter for the grapple, it will by its nature lock the grapple cylinder in position when it (the diverter) is in the de-energized state. And that you would gain nothing by buying a seperate lock/check valve assembly.

Side note: The hydraulic accumulator I was referring to would hold some fluid inside under pressure. The pressure is provided by a nitrogen charge against which the fluid presses, via a piston or by some other method.

That fluid will be pushed out of the accumulator and into a cylinder if whatever the cylinder is pushing agaist starts to compress. This would hold pressure on the cylinder end for a bit as it extended to make up for the crushability of whatever the grapple was holding.

Certainly there would be some drop in pressure as the fluid was expelled from the accumulator...I guess the minimum pressure would be set by the amount of nitrogen charge put into one end of the empty accumulator.

 

[PineRidge]

Bill I was all set to spend the money for the check valve and then you had to come along and throw a wrench in the works. /forums/images/graemlins/laugh.gif

However what you say makes perfect sense and I haden't even considered the thought. I think we'll just hold off on the check valve and give it a try without.

In a worst case scenario if the diverting valve doesn't hold the grapple like you described then we can add the check valve at that time, but I agree with you chances are slim that it will be needed.

You may have just saved us more than a few bucks, thanks!

 

[kennyd]

Bill and Mike,
Thats is my thought and hope, that the diverter will lock the cylinders in place. I will be using mine for my snowplow in a couple weeks, so I will be able to report then. If it holds the plow angled it surely will hold the grapple closed!

Sorry I came in this late...

 

[jinman]

</font><font color="blue" class="small">( Side note: The hydraulic accumulator I was referring to would hold some fluid inside under pressure. The pressure is provided by a nitrogen charge against which the fluid presses, via a piston or by some other method. )</font>

Bill, I was a little late to this thread, and the accumulator was the first thing that came to my mind as I read PineRidge's question. As I scrolled through the responses, I saw your name and somehow knew that you were going to suggest the accumulator. /forums/images/graemlins/smile.gif It is the ideal application for one.

The british call an accumulator a "capacitor" because it performs the same function in a hydraulic circuit as a capacitor in an electrical circuit. They are used extensively in aircraft hydraulic systems where surge demand on the hydraulic system could cause a momentary drop in pressure (landing gear and thrust reversers are two examples). A small accumulator on the grapple-close side would provide a little bit of a "soft" grip as the accumulator filled. When the grapple is opened, there would be a slight delay until the accumulator depleted. In a grapple, I don't know that you'd notice any difference. For anyone with special needs or a problematic grapple, I'd sure suggest the accumulator as a viable solution. /forums/images/graemlins/cool.gif

 

[rdbrumfield]

I may have missed something here, but check valves will not hold a cylinder if the packing isn't perfect. Most cylinders will bleed by on the inside somewhat. Just like your loader left up, usually they will be lower over time as the fluid goes from one side of the piston to the other, some worse than others. Giving an extra pinch now and then as you move your load is the only way I know to keep from dribbling your load.

 

[PineRidge]

<font color="blue"> I may have missed something here, but check valves will not hold a cylinder if the packing isn't perfect. </font>


Randall I agree with you but also feel that if double piloted check valves weren't a good solution to holding heavy implements in place they wouln't be adding them to top & tilt cylinders. We can set our box blade for a job and it doesn't drift while others without the same check valves have complained.

 

[SPIKER]

Hey MIKE:

since the winter ice/snow storm I have even MORE use for that grapple ofyou'res! /forums/images/graemlins/wink.gif so when you making the trip out west on 30 anyhow? /forums/images/graemlins/wink.gif /forums/images/graemlins/laugh.gif I have a BUNCH of limbs down in the woods now as well as all around the cabin /forums/images/graemlins/frown.gif so now I'll have to get some time to cut them up and haul em to a good burn spot... must have 1/2 a cord of limbs off my big (at one time very pretty white pines) all piled up at the bases of htem /forums/images/graemlins/frown.gif back in the woods I have a few tops down too 9will make soem good BBQ wood or bonfire wood...

anyhow the diverter SHOULD keep it closed when something is in there except for a bit of leakage back into the system through the divertor but that should be very small. bigger problem is sag due to shifting and or bouncing when traversing with grapple loaded up. this would require a quick switch over to crunch it back down more as you drag bounce the load to/from the spots... the accumeulator WOULD work but they are expensive and easly damaged as well as having to maintain them by adding air pressure using a nitrogen tank and a static pressure of say 800 psi (which is where the piston in the accumeulator is pushed fully forward into empty the oil back into the hydraulics) as you crunch down on the grapple then the accumeulator will build up fluid VOLUME under PRESSURE and as the pressure in the system increases the piston moves back and the PSI on the air side goes from ~800 PSI to the tractors max pressure maybe 1200 psi or 2000.) then the divertor would close leaving a lot of tractor hydraulic fluid inside the accumeulator under pressure as the load squishes then the pressure drops slightly and the piston gas exerts force onto the hyd cylinder keeping it closed tightly aginst the material...) this is a good use but the upkeep is a lot as the gas side will blead off and then you are just dumping the hydraulic fluid into a empty hole not to return untill the gas pressure is recharged and the divertor valve is let to relive the now newly gained gas pressures fluid excape back into the system...


I rebuilt A LOT of these when I was in the air force maybe say 300 or so in the 4 yrs I was in the hydraulic back shop. (must have rebuilt 1000 brakes though !) as far as rebuilding actuators remarkeably I did less of those than I did of the accumeulators or brakes...

anyhow now when were you bringing that grapple over for a real test again? /forums/images/graemlins/wink.gif

Mark m /forums/images/graemlins/smile.gif