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Calculating hydraulic tonnage rating

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kwschumm
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Posts: 5764 NW Oregon
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2006-08-27          133718

Log splitters are typically rated in tonnage, like 20 ton or 24 ton. How is that tonnage calculated? I'm thinking a 4" cylinder has a surface area of approx. 3.14*4=12.56, multiplied by 2500 psi gives 31400, divided by 2000 lbs/ton = 15.7 tons. Is that correct? Or is the rating further affected by the surface area of the splitting wedge that contacts the face of the log?

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hardwood
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2006-08-28          133723

KW; Your figures look correct to me. I don't know of another way to figure it. Frank. ....

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Murf
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2006-08-28          133725

Ken, you're right on the money.

The "tonnage" is merely a measure of brute force though. The efficiency is a whole other matter, things like splitting edge shape and size, friction, etc., all affect how well that tonnage performs though.

I have used big splitters that didn't work worth a pinch of you know what, and also smaller ones that worked just fine.

Quality and good design seem to make more difference than brute force by a long shot. The same can be said about working with them, a well thought out machine is a joy to use, a bad one can be a bear to use at the best of times.

Best of luck. ....

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hardwood
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2006-08-28          133731

We have a local fellow who is far from a dummy, but just never let his mind become too cluttered with formal education whom allways said the formula for the aeria of a circle was all wrong. His formula goes like this - Pi are round, Corn bread R square. Frank. ....

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DRankin
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2006-08-28          133732

Yes.... but cobblers..... which are essentially the same as pi's, are square. Or at least rectangular.

So I'm thinking it was a cobbler guy who thunk that circle deal up in the first place.......... ....

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kwschumm
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2006-08-28          133733

Thanks for the help and humor guys.

I was trying to figure out how speeco rated my log splitter for 25 tons. It has a 4.5" cylinder, so piston area s/b around 15.9 square inches. Working backwards through the numbers it looks like the pressure should be about 3150 psi. They don't give much to work with specs-wise. ....

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DRankin
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2006-08-28          133734

That seems like a high pressure. What are the hoses rated for? 3500 psi?

Most of our tractor/FEL's are in the 2400 psi range. ....

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kwschumm
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2006-08-28          133735

The lettering on the hose is faded away and the hose should be replaced anyway. It's stiff and old and abraded to the cord in one spot. I'm wondering if this little 8 hp engine can deliver that kind of pressure along with 16 gpm the pump is supposed to be rated for. ....

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kwschumm
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2006-08-28          133739

I called Speeco and they said everything on the splitter was rated for 3500 psi. ....

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Murf
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2006-08-28          133740

Ken, if you can get make and model numbers off the engine and hyd. pump I can look up the spec.'s and tell you what it works out to.

It may be that they are 'optimistically' rating the power like air compressor manuf. do, quoting "peak" hp ratings and such.

I did a little surfing the Speeco site and compared what they say with my catalogues here. If, for instance, your unit had the typical 5.5 Honda with an 11 gpm 2 stage pump, it would make a MAXIMUM of 3,000 psi, based on that a 4.5" cylinder would make 47,713 pounds of push power, or 23.86 tons.

This however is absolute amximum, everything is perfect conditions numbers. I suspect you would, real world operating conditions, get more like about 15 - 18 tons, certainly plenty of power still.

Best of luck. ....

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Art White
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2006-08-28          133741

Ken, most or all that I'm aware of use two stage pumps so that makes a difference to! The normal rule of thumb is two horsepower per gallon. ....

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Murf
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2006-08-28          133742

So Mark, are you trying to say those old Greek fellas that came up with all this stuff weren't necessarily the deep thinkers we were led to believe?

That they merely cobbled together a workable pi recipe?

Groan at will folks.........

Try the veal .......

Best of luck. ....

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kwschumm
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2006-08-28          133743

Murf, it's a Haldex 2-stage pump. There's two numbers on the plate, 020403 and 1002211. It doesn't say which is the model number and which is the serial number. The engine is a Honda GX240 rated at 8 hp. Thanks! ....

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Murf
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2006-08-28          133746

The Barnes catalogue I have shows that that pump has a "maximum continuos output" of 3,000 psi at 3,600 rpm on the input shaft.

According to Honda the GX240 has a governed no load speed of 3,900 rpm.

I would be surprised if it got much better than about 3,000 rpm under full load.

Based on that I stand by my earlier guess-timation.

Best of luck. ....

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kwschumm
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2006-08-28          133749

Thanks, Murf, that's good info. I've learned in this thread how to do these calculations, that the extra hydraulic cylinder I have is too small for the log splitter, that the hydraulic pressure hose on my log splitter is bad, and that you can't trust marketing specs. What else is new? ....

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DRankin
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2006-08-28          133751

Greeks? GREEKS!? I will have to look that up again. I Thought it said Geeks........... ....

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beagle
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2006-08-28          133760

Keep in mind the best pumps run at about 85% efficiency, cold. As the fluid gets hots, the efficiency drops. There are losses through the hoses, fittings, and most important, the valve. Add all of that to the efficiency of the drive motor.

Ratings on power equipment are variable,... being kind. A 20 ton log splitter will probably generate 75 to 80% of that in the field. Theoretically, it can produce 20 tons of pressure. The net "bore" of a hydraulic cylinder can also be somewhat different than the published bore. You need to get manufacturers specs to get the net bore.

Ever tried to get 21mpg's out of a 5.7 litre Silverado. You better have the wind at your back, going downhill, ..and leave the beagles at home. I haven't gotten it all right yet. ....

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kwschumm
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2006-08-28          133761

Do the manufacturers take efficiency into account when they rate the pumps? If you had a pump rated for 3000 psi at 3600 rpm could it really deliver 3000 psi if it were provided a steady 3600 rpm input? ....

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beagle
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2006-08-29          133765

Good question. Don't know if there is a published standard for testing (SAE maybe), but any pump would only be able to produce a rated flow at a given pressure, at one temperature. As the pump creates heat (losses) in the fluid, it's efficiency drops. ....

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kthompson
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2006-08-29          133766

12 or 20 tons, how does that compare to wedge and slege hammer for wood splitting? I thought it was a big improvement. But then men were men but trees were trees too. ....

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earthwrks
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2006-08-29          133767

I'm not sure of the numbers but generally the actual output will likley be MUCH less of published figures regardless of maximum pump PSI, hose burst strength, etc. IMHO it's the relief valve pressure setting that is the weak link in the chain which could be set at say 2800 or even 2500 PSI just as a margin of safety. Sort of like brake HP, SAE HP, and rear-wheel HP. It's all HP but whose formula do you use? (car mfg's---up until the recent flurry of law suits---would use whatever was to their marketing advantage) ....

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Murf
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2006-08-29          133772

As far as I can remember, pump spec's are purely hypothetical. All done on paper if you will.

Likewise flow rates, displacement times the rpm yields what they say the pump "can" do.

I don't know about the particular efficiency ratings, but I know if you look at the Mil. Spec. ratings of things, they usually represent the "real" numbers, such that a 9hp Honda is Mil. Spec. rated as a 5hp engine.

Best of luck. ....

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