Hydraulic pump question.

[sawyerkirk]

Hope it's OK to post this in this forum but I need help. I looked all over the web for an answer but came up empty. I am rebuilding my log splitter. I have a 6.5hp motor and I forget the cylinder size at the moment. It has about a 15 gallon fluid reservoir. I'm more concerned about splitting power than I am return time (if that matters). Which would be better for my set up a 11gpm, 13gpm or 16gpm? Also any suggestions on brand?

[Waynehere]

I too am in the middle of rebuilding my splitter. There are a lot of YouTube videos of homemade splitters and the neat things you can do with them. As for splitting power, you need high pressure from your pump, which most splitters have a high/low pump on them. Usually the low pressure/high volume for speed, and then the high pressure/low volume will kick in for the tougher wood. You have to match up HP with the pump volume specs you are looking at. They are different. And for splitting power, the larger the cylinder bore, the more square inches to push against, the more power you will have, but really all based on the pressure your pump will put out.

This thread has some better details about hydraulics.

http://www.arboristsite.com/community/threads/need-help-with-log-splitter-not-splitting-wood.206993/

So you really need to find out the bore size of your cylinder and do some math to see what you will need for your engine. Here was another useful video I used to determine mine.

http://www.youtube.com/watch?v=8umhGl-jHho

Good luck...

[Timberwolf]

sawyerkirk,

If you need help with the calculations let me know I can figure those out for speed and force (tonnage). You also need to understand how you are going to mount the pump, both mounting and drive from engine also, to make sure you get the correct pump.

[WESTMAPLES]

if you using a piston that's 5-6 inch bore with 2 in center rod and 26 in stroke with a 11gpm your cycle time would be 14 seconds or so roughly with a 6.5 hp at 3/4 throttle built 6 - 27-30 ton splitters in the last few years all are still in use by my customers today. theres plenty of different combos some are alittle faster but less power and vice versa I find 27 ton style to be easier to use, lighter to move around,and will split anything you put on it

[Big_Eddy]

Splitting force is a function of max pressure x cylinder size.
Cycle time is a function of GPM / Cylinder size.

Looking at each variable.


Max pressure is limited by the pump and valve ratings and will be 2250-3000psi.

Cylinder size is your choice. Bigger = more force, slower cycle time. A 5" cylinder has 1.5x the splitting force of a 4", but take 1.5x longer to cycle. The largest rod diameter for your selected cylinder diameter is best - stronger and also speeds up the return as there is less "non-rod" surface area. e.g a 5" cylinder with a 3" rod returns 30% faster than a 5" cyl with a 2" rod.

GPM (Pump size) is tied to horsepower. You must match your pump to your engine HP. Check the recommended horsepower for the specific pumps you are looking at and select the one that bests matches your engine.


Explaining the HP /GPM relationship a bit more. The pump load on the engine is a function of volume x pressure. Most splitter pumps are 2 stage pumps. At low load, they output high volumes for fast returns, then when the load increases the pressure steps up and the volume decreases. The pressure transition is sometimes adjustable but usually in the 600-900psi range, versus the max pressure of 2250-3000psi.

Each pump is designed for a specific engine HP. Both the high vol GPM x cutoff press and Low vol GPM x max press are less than the rated HP. See page 2 of this link for illustrations. http://www.concentricab.com/_downloads/Catalogs/HILO_PUMP_US.pdf

If you oversize the pump, the hydraulic load can exceed the output of the engine and engine RPMs will drop or even stall instead of splitting the log. It WON'T split faster.

Once you have the engine and pump matched, you can calculate cycle time pretty easily. Assume the high flow GPM for the return stroke and low flow GPM for the forward stroke. There are online calculators if you need them.

[Scribner's Mountain Maple]

I have a 16 GPM pump and it requires at least 8 hp. At least, so I have what I could find cheap. Happened to be an 18 HP vtwin. Works great. I built my own splitter too and the only thing I would add to what has already been said is to be mindful when buying hydraulic lines. Make sure they are rated for more than the max output of your pump. Also, I have a 3.5" bore with 42" stroke. Fast is nice. I just don't try to split rock hard pieces down the middle. I'll take speed over power most days. I think the ideal Cylinder bore is 4 or 4.5". 3.5 is too small and I hope to upgrade next yr to 4" or 4.5"

Ben

[sawyerkirk]

Just got my pump, they sent me a 16gpm instead of 13 can I use it with a 6.5hp?

[Big_Eddy]

What make and model? Maybe.

[KGodshall]

Just got my pump, they sent me a 16gpm instead of 13 can I use it with a 6.5hp?

You need to check what the pump is requiring. I had similar problem (larger pump/smaller motor). While I could cycle the piston, I could never get it to move over to the "high pressure" side of the pump.

Make sure you understand Big Eddy's post above: Motor size means relatively little to splitting force. If your valve or pump cannot exceed 3000 psi, you can only affect splitting force by size of your piston- 'pounds per square inch'.

Motor and pump size will help you in cycle times (faster vs slower), but if your pressure is being limited by component restraints, your piston size is the only available option for splitting force.

Best.

[wiam]

Just got my pump, they sent me a 16gpm instead of 13 can I use it with a 6.5hp?

I doubt it. I had a 7 hp on a 13gpm. I went to a 16gpm. It would run but when I moved the valve it would kill the motor. Now I have a 10hp and it works good, but I am going back to electric.

[Scribner's Mountain Maple]

I think Wiam is correct. I have a 16 GPM and was recently told the specifications call for an 8 hp motor as a minimum. I run mine on an 18 hp. Which is overkill. 10 hp would be ideal I think for a 16 GPM.

Ben