Back in the early 80's I split about 15 cords of Dutch-elm-disease killed American elm for my mother to use as firewood. Some of the rounds were more than 30 inches in diameter.
I used a homemade splitter my dad put together.Elm requires you to drive the wedge from the top all the way through the round. The halves do not come apart after 6 inches or so, the way maple or oak will. You need the cylinder to have a long enough stroke to accomplish this. Many log splitter cylinders have only a 12 inch stroke or so -- not enough for elm. My dad's splitter was like this -- I had to make two passes on many of the splits, cycling the control to pull the ram back and inserting a spacer prior to finishing the split. The splitting knife has to be taller than the diameter of the biggest pieces. You can't cheat like you can with oak or maple. My dad's splitter had a 14 inch extension retroactively welded atop the 16 inch main wedge. It is absolutely critical to have a real, two stage log splitter hydraulic pump. You need the pressure you get from the second stage to handle the tougher splits, and you need the volume characteristics of a two stage pump to get the ram moved back after the split. Remember that the ram has to move through a 16 inch travel on the way back, and you will quickly lose patience if the pump volume can't get it back in 5 seconds or less. The peak pressure you need depends on the size of the rounds. At least with American elm, a 5000 PSI two stage pump and a 5 inch cylinder struggled with the 30 inch rounds. You should have seen the 10 inch steel I-beam bending and groaning under the 50 tons of force. More modest diameter pieces won't be so bad. The really big stuff is heavy and awkward. You split into halves, then quarters, then eighths, then 16ths, then 32nds. At that point the size is still a little big for the stove, but you just can't bear to split it any more. The one 30 inch round you started with has turned into a substantial pile of partially split pieces sitting at your feet. And you have to pick every one of them up, set them on the rail, and split them again, and again, and again. Some means for staging the pieces so you don't have to lift them again would be a good addition to consider. A 7 to 11 horsepower motor is none too small for such a splitter. The more moxie the motor has, the faster the job will go. The control lever should offer an auto-return. You want the ability to shove the lever into a detent, so that the piston moves back into the loading position and then the lever goes back to neutral by itself. You will be using the "dead time" to stack the split pieces and ready the next chunk. You don't want to be standing there holding the lever, picking your nose, and watching the ram slowly return. One other thing about American elm is that it is about the dirtiest wood to have to bring into your house. You get bits of bark and moss and dirt and all kinds of junk scattered along the path from the woodbox to the stove. The only saving grace, in those days, was that the elm was abundant and free for the taking. It burned just OK, not as many BTU per pound as maple, but better than softwoods.
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