What is my tonnage on this splitter?

michaelthomas said:

I am looking to you math/engineering types out there.

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Why do you need an engineering degree when you have google? ;-)

http://knighthawksupply.com/calccylforce1.htm

michaelthomas said:

I am looking to you math/engineering types out there. What is the tonnage on this splitter... I have a 40" cylinder, 4" diameter with a 2"rod. It has an 8 hp engine pushing a 13 GPM at 1800 rpm single vane pump. What is the tonnage for this machine rated at?

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Not the right info. "Tonnage" is determined by the maxium pressure (relief valve setting) and the diameter of the piston. That's all is needed. Cylinder length,GPM, RPM, and horsepower have nothing to do with it, nor does the rod diameter.

Tell me the pressure at which it operates, and I'll tell you the max tonnage prior to lifting the relief valve. All that matters for splitting force (extending) is bore diameter and fluid pressure. The GPM number and cylinder length have to do with cycle time, and the rod diameter has little to do with anything other than strength, as a splitter is a "one-way" hydraulic machine, so you're not particularly concerned with how much tonnage it can produce on the back-stroke. Rick

Horsepower would be a limiter if the engine were so underpowered that it began to bog down prior to the system reaching its operating hydraulic pressure, but that ain't gonna happen on this rig...8 HP's plenty. Rick

If the 4" number you gave us is the inner diameter (bore) of your cylinder, and we assume the machine will develop 3000PSI, then the tonnage is about 19. Pi x r^2 is the area of the piston = 12.56 square inches. Area of the piston x pressure applied is the total force = 12.56 in^2 x 3000 lbs/in^2 = 37,699 lbs, which is 18.85 tons. I'd just call it a 20-ton splitter and get to work. Rick

fossil said:

If the 4" number you gave us is the inner diameter (bore) of your cylinder, and we assume the machine will develop 3000PSI, then the tonnage is about 19. Pi x r^2 is the area of the piston = 12.56 square inches. Area of the piston x pressure applied is the total force = 12.56 in^2 x 3000 lbs/in^2 = 37,699 lbs, which is 18.85 tons. I'd just call it a 20-ton splitter and get to work. Rick

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That's doubtful with a vane-pump and an 8 horse engine. Max pressure is most vane-pump systems is around 2000 PSI, not 3000 PSI. With 8 horsepower, if that pump is really 13 GPM at engine speed, it barely has enough power to make 1000 PSI before the engine stalls. To make 2000 PSI, the speed of the pump would have to be 1/3 of the engine speed with some sort of reducer.

But a single-stage vane pumps of what size? 13 GPM in itself is meaningless unless expressed at how many revolutions. Pump size is measured in cubic inch displacement per revolution.
If the 13 GPM rating is for something like the max engine RPM of 3600, then the pump is around 1 cubic inch per revoltion.

So, if that pump is hooked direct to that 8 horse engine, it would take 23 horsepower to make 2000 PSI. Obviously not going to work.

The "store-bought" 30 ton splitters use high-rated cylinders (3000 PSI) and two-stage hydraulic pumps that shift down to 3 or 4 GPM to make that 3000 PSI - in order to be classified as a 30 ton splitter.

To make a long story a little shorter - 8 horsepower is not near enough power to run a log splitter with a single-stage vane pump at any useful speed and pressure. A two-stage pump, yes -which is, in essence, two pumps hooked together. A tiny pump that can make high pressure with little horsepower, and a large pump when speed is needed and high pressure is not.

michaelthomas said:

So with a 22 vs a 28 ton, the cylinder is 1/2" bigger is this the only cause for additional tonnage?

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Tonnage is a result of pounds per square inch along with how many square inches of piston area? So, more inches, more tonnage (bigger cylinder). More pressure per square inch, also more tonnage.

2000 PSI was considered the safe working limit for most hydraulic equipment for many years, but with log splitters, they've upped things to the max so more tonnage can be claimed.

It is cheaper to raise tonnage by upping PSI, than by installing a larger cylinder, although the latter is more rugged and reliable.

I split a lot of big hardwoods, ash, red oak, pignut hickory, hard maple, etc. For most, a 20 ton splitter does fine. But for those curly stump pieces? You need a 30 - 35 ton splitter to do some of them. But, since they are not all that common for most wood cutters, it's up to you if it's worth having the bigger one for less than 1% ( the tough stuff).

michaelthomas said:

...So with a 22 vs a 28 ton, the cylinder is 1/2" bigger is this the only cause for additional tonnage?

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Depends on how it's designed & built. There are but two variables...piston surface area and fluid pressure. If you wanted, say 30 tons, it could be accomplished with a cylinder with a 12" bore and hydraulic pressure of about 531 PSI. If you wanted to use a 4" bore cylinder, you'd need to provide 4775 PSI. If you thought you wanted 30 tons from a 1" bore cylinder, you'd have to build a system that would handle 76,433 PSI. It's all in the r^2. Hydraulic systems that will operate at up to about 5000 PSI are pretty common. Above that, and you're drifting beyond the realm of your average homeowner's equipment. A 5" bore at 5000 PSI would get you about 50 tons. In any case, I really think that ~20 tons is ideal for most woodburners' splitting needs, so long as you're not going into the firewood business. It really is a plus if the machine can be operated either horizontally or vertically. The guys who are really seriously into this process have splitters in the 40 ton and up range, with log lifts and conveyors and 4-way or 6-way heads and who knows what all. I have an MTD 25-ton with a Briggs & Stratton engine, horizontal/vertical...and it's more splitter than I need. Of course, I'm strictly a wimpy softwood burner, so what do I know? It's what was available at the store when I wanted it, so I brought it home. If I were in the market, something right around 20 tons is what I'd be looking for. Rick

michaelthomas said:

I don't know the max pressure as I don't have a pressure gauge. It has a fairly standard detent valve. I imagine it has 3000 PSI. What does a standard splitter have with a 13 gpm pump?

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Where are you getting this 13 GPM number from? An 8 horse engine cannot make even 2000 PSI on a log splitter. A normal, store-bought 8 horse log splitter has a two stage pump that runs at 3 or 4 GPM when making high pressure.

fossil said:

Hydraulic systems that will operate at up to about 5000 PSI are pretty common. Above that, and you're drifting beyond the realm of your average homeowner's equipment.

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I don't find hydraulic sytems running at 5000 PSI to be anywhere near common in every day useage. Most farm tractors, bull dozers, hydraulic powered loaders, backhoes, etc. run at 2200 PSI to 2500 PSI with the latter the usual high-limit. Most conventional hydraulic cylinders carry an absolute max. pressure rating of 3000 PSI, and many are only 2500 PSI. Most conventional hydraulic pumps max out at 3000 PSI (hydraulic, not hydrostatic) and some at 2500 PSI.

Yes, there are exceptions, especially with hydraulic presses. But they are more the exception, and not common.

jdemaris said:

fossil said:

Hydraulic systems that will operate at up to about 5000 PSI are pretty common. Above that, and you're drifting beyond the realm of your average homeowner's equipment.

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I don't find hydraulic sytems running at 5000 PSI to be anywhere near common in every day useage. Most farm tractors, bull dozers, hydraulic powered loaders, backhoes, etc. run at 2200 PSI to 2500 PSI with the latter the usual high-limit. Most conventional hydraulic cylinders carry an absolute max. pressure rating of 3000 PSI, and many are only 2500 PSI. Most conventional hydraulic pumps max out at 3000 PSI (hydraulic, not hydrostatic) and some at 2500 PSI.

Yes, there are exceptions, especially with hydraulic presses. But they are more the exception, and not common.

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You're right. I was having a senior moment and letting my Navy experience color my comments. For 3 decades I lived in a world where high pressure air systems were 3000 PSI and above, and hydraulic systems that operated up to 10,000 PSI weren't hard to find, and believe me, they're common in everyday use...just not at home. I'm a Mechanical Engineer, and a former Chief Engineer of an aircraft carrier...please hold neither of those things against me. Thanks for bringing me back down to earth...er, ashore. Change my 5 to a 3 and I think we're close to being on the same page. I'm not one to quibble about a couple thousand PSI. ;-P Rick

michaelthomas said:

This is not a normal off the shelf splitter. This is something that some farmer raided his old equipment parts to make. It has a vickers v20 pump that is belt driven from the briggs. The vickers site lists the pump at 13 gpm at 1800? rpm. The engine is geared down with a smaller pully.

jdemaris said:

michaelthomas said:

I don't know the max pressure as I don't have a pressure gauge. It has a fairly standard detent valve. I imagine it has 3000 PSI. What does a standard splitter have with a 13 gpm pump?

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Where are you getting this 13 GPM number from? An 8 horse engine cannot make even 2000 PSI on a log splitter. A normal, store-bought 8 horse log splitter has a two stage pump that runs at 3 or 4 GPM when making high pressure.

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OK, that makes more sense then. That would be a 26 GPM pump if hooked direct to your 3600 RPM engine since RPM is a result of c.i. capacity along with RPMs. Those Vickers vane pumps were pretty common in ag and forestry equipment. Hooked to an 8 horse engine it would have to be geared down quite a bit to make 2000 PSI without stalling the engine. I'll add ,that if this thing is home made from salvaged parts, most sytems max out at 2000 PSI and that's probably ball-park of where it's set. I've got a 7 horse engine hooked to an old Cessna gear pump around the same size as your Vickers vane-pump with a 1 to 6 ratio, via belt drive and it just barely makes 2000 PSI when then engine starts to die and the belt starts to slip. Also runs the 5" cylinder very slow. But, it was the first splitter I ever made, over 30 years ago and I spent no money on it. I was a John Deere mechanic and had access to lots of scrapped parts.

fossil said:

For 3 decades I lived in a world where high pressure air systems were 3000 PSI and above, and hydraulic systems that operated up to 10,000 PSI weren't hard to find, and believe me, they're common in everyday use...just not at home.

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I've worked on plenty of high-pressure machines, usually in specialty stuff in industry. 5000 PSI is not common with mobile consumer equipment. I suspect it would be dangerous for several reasons. Most hydraulic cylinders carry a max rating of 3000 PSI and many are only rated at 2500 PSI. Most gear and vane pumps max at 2500 PSI (including the aforementioned Vickers). Most Vickers pumps max at 2000 PSI but 2500 PSI units can be special ordered. Then there is the problem of hydraulic hoses. Many carry a max. work rating of 2500 PSI, and some better ones are rated 3500 PSI. Anything with rubber in it that exceeds that threshold is often hard to find locally. There are 5000 PSI hose assemblies available, but they are not common. All it takes is one hose to need replacement and someone has a new one made with standard hose - and you've got problems.

The other issue, besides the max pressure rating is one of durability. To design something that's going to last awhile, you don't want it running at max capacities. That's why the majority of consumer equipment with hydraulics is set at 2000 - 2200 PSI. With these 30 ton log splitters running 3000 PSI, which IS at max, the assumption is that reaching that high pressure would be only in rare occasions with very hard splits. Using a larger cylinder with a lower max pressure would be more reliable, but it also costs a lot more money to build them that way.

I agree with everything you say here, and as I stated previously I clearly misspoke when using a parameter as high as 5000 PSI in reference to operating characteristics of common consumer equipment. Rick