Splitter - how much force when cylinder retracts?

[BlueRidgeMark]

My Huskee is advertised as a 35 ton splitter. Uses a 5" cylinder. (To actually deliver 35 tons would require 3565 psi working pressure. I don' theen so, Lucy!)

Anyway, whatever the actually tonnage is on the forward stroke, it has to be less on the reverse, even if the system pressure is the same for both strokes. (Because the rod takes up some surface area on which the hydraulic fluid can't exert pressure.) For example, given the working pressure above, and a 2" rod, I should get about 21 tons on the reverse. If the pressure is actually, say, 2500, I'll get 30.8 forward and 18.5 reverse.

So, questions for the hydraulics experts:

1. Is the pressure the same on the reverse stroke?
2. If not, what is it?
3. How much tonnage on the reverse stroke?
4. Can I put this to use in another application where I need PULL instead of push?

I'm wondering if I can use it to pull small (up to maybe 3") oak stumps. I have dozens of them.

 

[greengoblin]

i dont know the answers to the questions, but why not design it so you are using the pushing force instead of the pulling force?

 

[drmiller100]

absolutely you can pull with the ram.

i didn't verify your math, but your logic in general is correct.

 

[BlueRidgeMark]

i dont know the answers to the questions, but why not design it so you are using the pushing force instead of the pulling force?

I want to keep it usable as a splitter, so I don't want to make any permanent changes. The way this thing is built, I can just remove the bolt that attaches the wedge to the rod, and put a shackle in its place. Pull the splitter up to the stump, tilt it down, then attach a hefty cable to the shackle, and then the stump. Fire it up, retract the rod, and - I hope - out comes the stump. No major fabrication, no welding (don't have a welder), very simple.

As long as it won't hurt the splitter, I'll give it a try, but I don't want to take any chance on damaging the splitter, so I'm hoping a hydraulics expert will stop by and tell me one way or another.

 

[fletcher0780]

I want to keep it usable as a splitter, so I don't want to make any permanent changes. The way this thing is built, I can just remove the bolt that attaches the wedge to the rod, and put a shackle in its place. Pull the splitter up to the stump, tilt it down, then attach a hefty cable to the shackle, and then the stump. Fire it up, retract the rod, and - I hope - out comes the stump. No major fabrication, no welding (don't have a welder), very simple.

As long as it won't hurt the splitter, I'll give it a try, but I don't want to take any chance on damaging the splitter, so I'm hoping a hydraulics expert will stop by and tell me one way or another.

You could attach a pulley to the splitter itself or something behind it to reverse the direction of force and use the forward stroke. What do you plan on anchoring your splitter with?

 

[greengoblin]

You could attach a pulley to the splitter itself or something behind it to reverse the direction of force and use the forward stroke. What do you plan on anchoring your splitter with?

thats kinda what i meant

 

[kevin j]

your logic is correct. There is so much advertising BS and dishonesty.
35T is 3600 psi,

pressure x area is push.
pressure x (closed area minus rod steel area) is pull.

2500 psi would be about 25 t, not 30.8 though. 21T in retract at 2500 psi.

Main system pressure is set by the relief valve, usually in the spool valve, so it is the same both directions.

Stability is of course the issue. Both when keeping the line of force inside the foot in the vertical position, but also in what happens to the ground when you pull the stump? The whole thing might move because the root ball picks up the earth the beam is resting on.

Concept is intriguing though, and 90% of the 'hydraulic machine' is already there. Maybe some sort of tripod/outirgger pads to stabilize and get the forces to ground outside of the root ball.
Cables and pulleys and levers can work also, but need to make sure the pushing reaction eventually gets to pads on the ground. Else it would just lift the entire machine or tip it over to the side.

Maybe a pulley at end of the fixed plate, routing cable down to the ground, but also pin the tripod/legs/outriggers to the end of beam at the same point. You would still be retracting cylinder, but operating with splitter in horizontal position. Pull the cable, and the outriggers keep the splitter end from going down.

I need to think about this some more. Won't hurt anything hydraulically, but stability and forces are a big issue. Being careful in operation can work. Or maybe backing the RV setting down a lot when using in this mode.

great idea, I think shoudl pursue it.

k

 

[BlueRidgeMark]

Be careful with that plan Mark. My splitter pushes 25 ton and probably pulls about 20 tons. This is a lot of weight and there is the possibility that when you are doing heavy pulling your splitter might lurch sideways or otherwise jump around. For your plan to work the best the splitter's foot would have to be directly centered over what you are pulling or side loads are going to be generated. If not exactly centered under the 'foot' the tires and axle of the splitter may get highly loaded. I'm assuming the 'foot' of your splitter would be on the ground to absorb the pulling load the ram applies. It takes a lot of power to pull stumps and a log splitter delivers, just be careful with that power.

Understood, Dan! There are safety issues and alignment issues. I don't want a bent rod!

Here's what I have in mind: The cylinder is anchored with a clevis at the top end. Picture here.

Picture that in the vertical position. If I remove the bolt that holds the wedge, the cylinder can pivot out a bit at the bottom end. With the foot of the splitter parked next to the stump, it will only be slightly out of a straight vertical pull. The cylinder has a cable attached to a shackle (as described in the first post), and then to the stump. Like this:



(I didn't take time to draw the wheels and the rest of the splitter, but you get the idea, anyway.)

With the cylinder anchored only at the top end, this should be self-aligning, so I don't think I'll bend the rod.

Getting a good grip on the stump will be a challenge. I'm thinking of a choker arrangement, with something like 3/8 steel cable.

Whatcha tink?

 

[BlueRidgeMark]

Won't hurt anything hydraulically,

That's the key thing I need to know. Thanks!

but stability and forces are a big issue.

Agreed! You and Dan & I are on the same page, there.

I think I'll give it a try, very carefully, with the simple setup shown above. I'll take it slowly, at low throttle, and watch to see what kind of forces show up.

The root balls on these are not extensive, so I think I'm okay there. There's mostly tap root on the ones I've pulled already. (Using a come-along and a lot of sweat.)

A back-hoe would make this a lot easier, and I need to rent one for the bigger stuff anyway, so I'm not going to push this attempt very far. If it can be done simply, it will help a lot. If it's going to be major surgery to create some new machinery, it won't be worth it.

But if a shackle and some cable can get 80 or 90% of these buggers for me? Yeah, that would be worth it.

 

[BlueRidgeMark]

your logic is correct. There is so much advertising BS and dishonesty.
35T is 3600 psi,

pressure x area is push.
pressure x (closed area minus rod steel area) is pull.

Yeah, we hashed that out a while back, in this thread.

Like I said there, I'm no hydraulics expert, but the arithmetic is pretty simple. It's the stuff I don't know about that worries me!

 

[reaperman]

Oak stumps even small ones are nasty. You could use the full force of your forward or down stroke if you used a pulley instead of the back stroke to pull the stumps. I dont know much about pulley engineering, but I think you could rig something up that will increase your power with a pulley system.

 

[kevin j]

with the sketch you have, the pull force is still offset from the force of the shoe on the ground. Thus is will pull the splitter over to the right. Since the cable can never get under the shoe, they will never align and keep trying to tip. You need to have something pulling the top to the left to balance that. But if you keep the splitter hitched to the truck/tractor, (I assume the hitch if to the left) and run a bar/chain from top of the beam down and to the left, the forces would use the truck to balance out. Caution, there would be uplift on the ball hitch at the truck, but because it is so far away, long lever arm, so the force would be smaller.


Mfrs ratings of 'tons' are a sore point for me. There is so much pure marketing BS where they rate at the highest components RATED pressure, not the relief valve setting for maximum actual pressure, or the engines capability to turn that size pump at that psi.

Sort of claiming a pickup has 'towing capability' of 15 tons just because it has a 2 inch diameter drawbar pin, but a Yugo engine and drive that can't actually pull it.......

I had a salesman say one time 'oh but our cylinders are more efficient than the other guys'....' excuse me but cylinders are p x a, that's it...... If there is a cylinder greater than 100%, I'll buy stock in the company.


Basically, compare cylinder size. 2500 to 2750 is safe maximum territory for all consumer machines and hoses. So cylinder size is tons, ignore the advertised number bs.

k

 

[BlueRidgeMark]

with the sketch you have, the pull force is still offset from the force of the shoe on the ground. Thus is will pull the splitter over to the right. Since the cable can never get under the shoe, they will never align and keep trying to tip. You need to have something pulling the top to the left to balance that.


Hmmm. Yeah, you're right.

But if you keep the splitter hitched to the truck/tractor, (I assume the hitch if to the left) and run a bar/chain from top of the beam down and to the left, the forces would use the truck to balance out. Caution, there would be uplift on the ball hitch at the truck, but because it is so far away, long lever arm, so the force would be smaller.

OR, a strong bar of some kind from the top of the beam to the ground on the other side of the stump.... Hmmm...

I had a salesman say one time 'oh but our cylinders are more efficient than the other guys'....'

You know when a saleman is not lying, right?

 

[CylinderService]

Mark,
Yes, I'm still around, busier than ever at my desk, and trying to get a new catalog put together, so there hasn't been much time for fun.
I think Kevin J has given you the right stuff. It won't hurt your cylinder as long as you don't bend it. The relief valve on your directional valve limits you to the same pressure on both push & pull strokes, and the rod diameter reduces the pull force.
In your diagram, if you could make the "foot" stick out farther on either side of the stump, then you could pull on the stump without tipping the machine over onto the stump, which would happen with all the other ideas I think. Think of standing over the stump and pulling on it with your hands. Unless your feet are on either side of the stump, you'll tip over too.
Your idea of a bar to the far side of the stump would accomplish the same thing. A tripod would be even better.
If you use a cable & pulley you could double your pulling force by bringing the end of the cable back up to the splitter frame. You'd have to go around a pulley block at the stump, and actually attach the pulley block to the stump.

Thanks for the e-mail, Mark.

[email protected]

 

[wireedm]

Don't get hit with the cable if it breaks, it MIGHT hurt a little.

And with the picture above, you would need a BIG stabilizer going to the other side of the stump load, kinda like a tripod effect. Otherwise it's just going to pull it right over.

For instance, if you had the line on a 20 degree angle going to the stump and it took 25 tons to pull it up, then you would have 20 tons pulling straight down on the rig, AND you would also have 5 tons pulling the top of it towards the right. Technically, that means that your 8000lb F250 wouldn't even be able to keep it from tilting over.

 

[BlueRidgeMark]

For instance, if you had the line on a 20 degree angle going to the stump and it took 25 tons to pull it up, then you would have 20 tons pulling straight down on the rig, AND you would also have 5 tons pulling the top of it towards the right.

Yeah, I see what you mean. However, there is another limiter to the amount of force - the breaking strength of the stump-ground bond. If it takes 3 tons to get the stump to break free, there will never be more than 3 tons of force applied.

That means my brace only has to support the 'break free' force, not the whole 20+ tons.

Technically, that means that your 8000lb F250 wouldn't even be able to keep it from tilting over.

Wish I had one!

I figger sumthin' out, and let you guys know. Thanks for the input!

 

[drmiller100]

40k pounds of digging force is a LOT.

I think like someone suggested you would want to put legs out beside or on the other side of the stump to keep your whole rig from tipping over backwards.

 

[wireedm]

A 65hp Kubota with a bucket can only lift about 3000lbs and will just vibrate an 8" Bradford Pear tree when trying to DIG it out.

Remember, you're trying to PULL it out with brute force without any "digging". A root system has to keep a 12,000ish (depending on diameter) pound tree from falling over when the strong winds hit the top. That's a LOT of pressure at the root system to keep it from tipping.

 

[triptester]

I watched as a crew was clearing a lot . They had a medium sized dozer and a crawler backhoe. The dozer would raise it's blade to push as high as it could to uproot trees. Where there were only stumps the dozer had trouble. Then the crawler backhoe would try to pull them out often just tipping the hoe up unto the tips of the tracks. On a lot of the stumps the backhoe had to dig to cut roots before it could pull the stumps. The backhoe had 4 and 5 inch bore cylinders I don't think the log splitter setup will work.

 

[ray benson]

With the capability of 20 tons of pulling force what size steel cable would you need? Here is a wire rope sling rated at 7.2 tons if you choke it. The wire rope is 1" dia.
http://www.grainger.com/Grainger/items/1DNE4