Adding Cylinder to Grapple

[Olalla Tractor]

Hello All! My Kubota B21 has a power beyond line for the FEL. It runs the top end of a homemade grapple. Currently there is a single 2" diameter cylinder that opens and closes the "tines" of the top. I changed the 2" cylinder to a 4" cylinder for added gripping power but it was too slow to function well. I am wondering, if I add a second 2" cylinder to the top end of the grapple and run it off the same line as the original (with a hard line between the two) will the resultant speed of the cylinder function be the same as a single 4", or can I expect the two 2" cylinders to be faster than the 4? Thanks in advance

 

[Leejohn]

Anyway you look at it you are pumping the same amount of oil to move a 4" or two 2". Speed well be the same.

 

[ovrszd]

Too many variables to give a definitive answer. But using the "shadetree mechanic" philosophy, yep will be similar.

 

[kennyd]

Here are some calculators to help figure things out: Baum Hydraulics Corp :: Spec Calculator

You can figure the volume(s) of the cylinder(s) with this one: Calculating the Volume of a cylinder

A 4" cylinder on a grapple just seems crazy-it must be very stout to handle that kind of force. Can you post some pictures of it?

 

[kennyd]

Too many variables to give a definitive answer. But using the "shadetree mechanic" philosophy, yep will be similar.

^^^^
This!

 

[MtnViewRanch]

Hello All! My Kubota B21 has a power beyond line for the FEL. It runs the top end of a homemade grapple. Currently there is a single 2" diameter cylinder that opens and closes the "tines" of the top. I changed the 2" cylinder to a 4" cylinder for added gripping power but it was too slow to function well. I am wondering, if I add a second 2" cylinder to the top end of the grapple and run it off the same line as the original (with a hard line between the two) will the resultant speed of the cylinder function be the same as a single 4", or can I expect the two 2" cylinders to be faster than the 4? Thanks in advance

Not sure what the PSI its set at for your tractor, but even at just 2000psi which is low, the 4" cylinder exerts about 30,000lbs of pressure. Pretty sure that if you were to bite down on something hard, that you would be crushing it. A single 2" cylinder exerts a little over 6000lbs of pressure. I would think that that would be enough on it's own, but if you want 2, then about 12,560lbs of pressure.

Now of course these figures are at rod ends, so depending on the leverage the grapple tip pressure will go down.

Square inches of a 2" cylinder are 3.14 and 12.56 for the 4" cylinder. So you will have about 1/2 of the force of the 4" cylinder and 2 of the 2" cylinders will move about twice as fast as the 4" cylinder does. To the best of my knowledge, you have to get intro a pretty big tractor before any 4" cylinders are used. Definitely not what you would normally see on any B series tractor, maybe on an M5 or 6 and even then probably not.

Good luck with your modification, maybe just go with a 2 1/2" dia cylinder and get about 10,000lbs of force?

 

[joefromga]

Hydraulics are amazing.

 

[4570Man]

Duel 2"s of the same length will operate faster, but have less force than the 4". OMO this is a bad idea. It's probably going to crumple your grapple.

 

[Olalla Tractor]

Excellent info! Thanks so much. KennyD I'll post a pic if I can get it figured out. Thanks!!!

 

[CJONE]

A 2" at 10" of stroke needs 32.5 ci of oil. A 4" at 10" of stroke needs 130 ci of oil. Soooo a 2" bore will be 4x as quick as a 4". So 2 2" bores will be 2x as quick. A 4" bore will develop 30,000 lbs of force at 2400psi. My guess is you don't need that unless you are crushing concrete or seeing how bad you can bend your grapple clamp. CJ