Twin hydraulic cylinders on log splitter?

JoeE. · Jun 16, 2017

I have been toying with the idea of making a more powerful log splitter, with an eye on splitting larger pieces.

I've collected a couple of pair of large hydraulic cylinders with the idea of making a more robust machine that can split about anything I can get loaded on the beam. My stove can take 44" long pieces of wood.

Anyhow... I've got two 4"x48" cylinders (2500psi).

The problem I run into is that the current single 4" (2500# Prince tie rod style) cylinder on my machine seems to lack the force needed to split some of the wood I get. I've got the bypass on the control valve set right at 2500# and it bypasses a lot of the times. Wedge is nice and sharp... but the wood is tough.

I'm thinking that I could double the force by stacking one cylinder atop the other... both pushing on the same wedge. I would effectively have 8" of area for the hydraulic pressure to act on instead of 4".

Thinking about all this.. would I have problems with one cylinder trying to do more work than the other to any extent? I'm trying to figure if I need one of those "flow dividers" to prevent that.

I'm trying to figure out how many GPM pump and control valve to buy. I will go time the current splitter and see how fast it extends to determine what it would take to get a twin cylinder machine to do the same.

By my calculations, each cylinder would take 2.61 gallons of oil to extend it fully... so a little more than 5 gallons for the pair.

I've got a pair of 8"x 44" cylinders... and I thought about maybe using just one of them... but this would be more unique.

dgfoster · Jun 16, 2017

You probably already considered that the 8x44 would provide twice the force that two 4x cylinders would produce. Seems like an 8 would be a huge log splitter cylinder given what I see in general use and would fill four times slower than your current 4.

Denis

moonlight machine · Jun 16, 2017

I just filled my propane tanks for .94 / gallon. WTF are you screwing around with wood? I paid for set it and forget it heat for a year on 1 days earnings.

tonymor · Jun 16, 2017

I don't think you'll have to worry about flow dividers for this application. You'll get equal pressure in the two cylinders under load and they'll do equal work. Close enough to it anyways for a log splitter.

HuFlungDung · Jun 16, 2017

I'd think about going to a single 5 or 6 inch cylinder. The dual cylinder setup could result in some sort of unequal extension situation that might bend something, unless you have a really well built carriage for the wedge, that could never bind on the pole. I'm no hydraulics expert, but when the cylinders are working at full pressure, that's when you'll notice these issues. Mind you, the working pressure will mostly be halved when you have double cylinders and the same resistance.

surplusjohn · Jun 17, 2017

it helps if you keep your hoses the same length, and if they are the exact same cyclinder, but they will equalize well enough for this application. a single cylinder would be a more robust approach. it seems that since you are splitting longer pieces, you are fighting a lot more of the splitting resistance of the wood. would a wedge on both ends work? ie on the ram and the anvil sides?

TDegenhart · Jun 17, 2017

HuFlungDung said:
I'd think about going to a single 5 or 6 inch cylinder. The dual cylinder setup could result in some sort of unequal extension situation that might bend something, unless you have a really well built carriage for the wedge, that could never bind on the pole. I'm no hydraulics expert, but when the cylinders are working at full pressure, that's when you'll notice these issues. Mind you, the working pressure will mostly be halved when you have double cylinders and the same resistance.

No, it might take twice as long to fill, but the pressure will be the same.

Regarding force v cylinder size, assuming you are working on the side of the piston opposite the rod, the force area goes as the square of the diameter. So an 8" cylinder is four times as much force as a 4".

Tom

JoeE. · Jun 17, 2017

TDegenhart said:
....Regarding force v cylinder size, assuming you are working on the side of the piston opposite the rod, the force area goes as the square of the diameter. So an 8" cylinder is four times as much force as a 4".

Tom

So, wouldn't two 4 inchers push just as hard as one 8 incher? I can almost see where it wouldn't.... I just can't quite wrap my mind around the reasons why.

WILLEO6709 · Jun 17, 2017

JoeE. said:
So, wouldn't two 4 inchers push just as hard as one 8 incher? I can almost see where it wouldn't.... I just can't quite wrap my mind around the reasons why.

it varies with the square of the radius- piston area = pi * r * r
so for a 4 inch is 2*2*pi= 4 pi= 12.566 sq inches x system pressure
for a 6 inch is 9 pi= 28.27 sq inches= 2.25 times a 4 inch
for an 8 inch- 16 pi= 50.265 inches= 4 times a 4 inch

don't forget the safety aspects- this is enough force to leave a mark.

idacal · Jun 17, 2017

it would work. you would have a true 30 ton splitter if I did the math right .You wouldn't need any flow splitters it would even it out by the psi. but one 8" cylinder would be 62 tons . a 2 speed pump like this 28 GPM DYNAMIC 2-STAGE PUMP | 2 Stage (Log Splitter) Pumps | Hydraulic Pumps | Hydraulics | www.surpluscenter.com will do a low pressure cycle on the 8" would still be like 40 seconds a cycle ,(,I think thats right but my math could be faulty tonight) but at the low pressure side 900 psi it would still be at 45000lbs of push so most things would split at that and still more than you have now. your biggest problem and most expense will be getting a frame setup that will not deflect like a wet noodle with that much tonnage.

ewlsey · Jun 17, 2017

I used to worry about splitting every single piece of wood. Not anymore. If it won't split after a few tries, I just throw it in the burn pile and move on. There's plenty of wood in this area.

Davis In SC · Jun 17, 2017

Think of Pi as Pies... Two four inch pies are less than one 8 inch pie...

Ziggy2 · Jun 17, 2017

I think your biggest problem will be how to keep your log splitter together.

One of the downsides to the dual cylinder is is how to build the frame structure so that it can handle the increased forces.

Stacking another cylinder on top of the existing cylinder is going to introduce a significant bending moment into the main I-beam, especially since the top cylinder is going to be at least twice as far away as the existing cylinder.

Your reasoning is sound but I think to make this work will require a complete re-work of your existing log splitter.

There is also the safety issue to consider that other have mentioned. You are talking significant forces that are going to be transferred into the steel structure. When something goes wrong, the energy will be going someplace and that might be you or a helper.

Have you ever been around a 50ton press operating at rated capacity when trying to remove a bearing when something gives as in the bearing cracks? You definitely don't want to be in the line of motion of the bearing fragments. Your log splitter will be the same way.

Cole2534 · Jun 19, 2017

Davis In SC said:
Think of Pi as Pies... Two four inch pies are less than one 8 inch pie...

I like to think of them as squares with the corners knocked off to approximately 78.54% of their original size.

HuFlungDung · Jun 19, 2017

TDegenhart said:
No, it might take twice as long to fill, but the pressure will be the same.

Regarding force v cylinder size, assuming you are working on the side of the piston opposite the rod, the force area goes as the square of the diameter. So an 8" cylinder is four times as much force as a 4".

Tom

There is no pressure built until a resistance is encountered, apart from port restrictions and such. Pumps don't "put out" full psi unless there is enough resistance to flow to cause the pressure to rise that high.

TDegenhart · Jun 19, 2017

HuFlungDung said:
There is no pressure built until a resistance is encountered, apart from port restrictions and such. Pumps don't "put out" full psi unless there is enough resistance to flow to cause the pressure to rise that high.

Of course! Any damn fool knows that!

Tom

HuFlungDung · Jun 19, 2017

TDegenhart said:
Of course! Any damn fool knows that!

Tom

Good, we agree, then generally, his twin cylinder will be operating at about 1/2 the working pressure of the single unit, but it will have the capability of more oomph when required. This is what I said originally.

Pokeypurplepants · Jul 12, 2017

Many years ago I built a splitter. Had a 10 hp Kohler, obtained a pump to mount to it and 4 x 24 cylinder. Some knotty stuff it wouldn't split but the speed was scary. Added a twin cylinder above the original and made a cross of the wedge - 4 pieces per split.
That slowed it down to a safe speed and thereafter was unable to find anything it wouldn't split.
Was a pig on gas though.

Tony Quiring · Jul 12, 2017

HuFlungDung said:
Good, we agree, then generally, his twin cylinder will be operating at about 1/2 the working pressure of the single unit, but it will have the capability of more oomph when required. This is what I said originally.

1/2 the volume and equal pressure per Sq inch on the wet side of the ram.

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Scruffy887 · Jul 13, 2017

Better to find a way to put 2 cylinders side by side than one on top. Keeps the force closer to the rail.

Twin hydraulic cylinders on log splitter?

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