3pt Log Splitters

[TheOldHokie]

One of the main issues with 3pt log splitters is slow cycle times. It takes a pretty hefty flow rate to get reasonable speed and most small utility tractors don't have the output needed. My newly acquired L3901 @ 6+ GPM was a big improvement over the old B7200 @ a scant 4 GPM but still pretty slow. It turns out the valve on the splitter had developed a bad leak so when I went to replace it I decided to try one of the "high speed" valves.

Hydraulic Log Splitter Control Valve w/ Return Stroke Detent, 21 GPM

FREE SHIPPING Hydraulic Log Splitter Control Valve w/ Return Stroke Detent, 21 GPM

summit-hydraulics.com

They have a regen circuit on the extend port and a 4 position spool. The 4th position actuates the regen for rapid extension and when the wedge hits the log and stalls you drop back to the third position for full splitting pressure. Same basic idea as a two stage pump but it only works one direction. I had my doubts but they are not expensive and I needed a new valve anyway so I figured why not. Much to my surprise the increase in speed is substantial. Here is a short video clip showing the relative speeds of extension vs retraction. I have only split a few rounds as a test but right now it looks like a big winner.

Dan

 

[Old_Paint]

Thanks for the review. Not sure that speed is an issue for me, but certainly, anything that holds oil that's going back in my tractor is. I'd prefer a PTO powered unit with it's own hydraulic reservoir and pump. I'm a little disappointed to see that there doesn't seem to be many options for such a beast. One would think that anyone with a tractor would welcome the sight of something that has self-contained hydraulics. and doesn't affect the maintenance of the tractor. I've seen a few units, but the pump alone cost nearly what the splitter does. Perhaps that's the reason, but somehow, I'm just not quite sure I understand why something with its own engine, a pump, and the splitting hardware can cost less than one without the engine, but a simple drive adapter instead.

 

[TheOldHokie]

Thanks for the review. Not sure that speed is an issue for me, but certainly, anything that holds oil that's going back in my tractor is. I'd prefer a PTO powered unit with it's own hydraulic reservoir and pump. I'm a little disappointed to see that there doesn't seem to be many options for such a beast. One would think that anyone with a tractor would welcome the sight of something that has self-contained hydraulics. and doesn't affect the maintenance of the tractor. I've seen a few units, but the pump alone cost nearly what the splitter does. Perhaps that's the reason, but somehow, I'm just not quite sure I understand why something with its own engine, a pump, and the splitting hardware can cost less than one without the engine, but a simple drive adapter instead.

This splitter was miserably slow on the B7200. Prior to buying the L3901 I was toying with the idea of adding a reservoir and running it off a PTO pump. Pump is currently $420 and reservoir another $150 so not a huge expense. Bigger tractor and this valve have negated my interest in that idea.

Dan

 

[GreensvilleJay]

Best setup I've seen is having a gas powered log splitter mounted to the tongue of a dumptrailer. easy to transport to the trees, unload, frees up tractor for other duties .hile 2 guys make short work of cut/split/load. Gas/oil/saws,tools all stored in boxes infront of fenders, so 100% of the dumpbox could be loaded with wood.
I don't see how that 'fancy valve' can work any better than a properly sized valve. It's rated for 21 GPM and your tractor puts out 4 or 6 GPM, so , so that valve cannot generate any more speed.

 

[Matt Ellerbee]

I don't do a whole bunch of fire wood, but I much prefer a stand alone unit. Frees tractor up to gather logs and keeps the hours off/fuel cost down.

 

[TheOldHokie]

I don't see how that 'fancy valve' can work any better than a properly sized valve. It's rated for 21 GPM and your tractor puts out 4 or 6 GPM, so , so that valve cannot generate any more speed.

You would be mistaken sir - research regenerative hydraulic circuits. In the regen position the valve redirects the waste oil exiting the rod end of the cylinder back into the base end where it combines with the pump in flow increasing the effective flow rate into the cylinder. It comes at a loss of actuating power because the two flows are opposed inside the cylinder and the force exerted on the rod is reduced by the ratio of the piston working areas of the rod versus base ends. In situations where actuator speed is needed over force that speeds up rod movement and is a common feature on loader valves where it is used to speed up bucket dump times. Kubota uses regen on many of their loader valves including my new LA525.

Edit: I have added an animation to help you visualize the operation

Dan

 

[Old_Paint]

You would be mistaken sir - research regenerative hydraulic circuits. In the regen position the valve redirects the waste oil exiting the rod end of the cylinder back into the base end where it combines with the pump in flow increasing the effective flow rate into the cylinder. It comes at a loss of actuating power because the two flows are opposed inside the cylinder and the force exerted on the rod is reduced by the ratio of the piston working areas of the rod versus base ends. In situations where actuator speed is needed over force that speeds up rod movement and is a common feature on loader valves where it is used to speed up bucket dump times. Kubota uses regen on many of their loader valves including my new LA525.

Edit: I have added an animation to help you visualize the operation

Dan

I reckon the 'regenerative' effect of that could probably be calculated, including the speed difference using rod end/head end compensation, but gonna need some more info on pressures, etc. Fluids don't compress, so GPM into a specific volume/cross sectional area should tell you how fast somethin's gotta move. I'm not quite sure "regenerative" is the correct word for that diagram, though. I'm hoping that animation is over-simplified, because what I see would ALWAYS have pressure on the Rod end, and only bleed the head end to tank on retract. A larger port on the head end would certainly allow the head end to bleed to tank faster, and this is pretty much common practice because of the difference in volume on each end of a cylinder. Pressurizing the head end would indeed push the smaller CSA (cross sectional area) of the rod end if there was some relief to tank, but I'm not quite sure I buy into it making any significant contribution by pushing the oil right back into the same line. Once it contacts anything and the pressures equalize on both sides of the piston, that cylinder cannot move without bleeding volume to tank from the rod end. I think I'm not seeing all of the circuit for the 'regenerative' function. Perhaps a pressure relief and a check built into the valve? If that's the case, there's always going to be some pressure on the rod end in that diagram, meaning loss of efficiency on the head end in the name of faster extend speed (until it hits the wood). I've seen a lotta things done with hydraulics working around large rolling mills (steel and aluminum) as well as paper machines, some cylinders designed to put out millions of pounds of force, but with a stroke less than an inch long, some with nearly 30 foot rods. It always comes back to the same calculation, though that you can have more force extending, and more velocity retracting. Some of them really made me scratch my head. But hydraulics is not unlike electricity, and I do understand both will take the path of least resistance. I've done my share of regulating hydraulics and controlling the pumps with electricity. Didn't have a choice but to understand the hydraulic side. Return to tank is about as fast and least resistant as it can get. The larger the line (and valve port), the higher the return capacity. I've seen many applications with larger lines on the head end of the cylinder, simply because of the need for higher flow on that end. Get it large enough, then back-pressure of the return becomes negligible with respect to volume from the pump. What I see in that diagram is waiting to stall on a hard piece of wood, and the advertised tonnage of pressure is probably based on cylinder size only. Like I said, though, I think it may be over simplified.

 

[TheOldHokie]

I reckon the 'regenerative' effect of that could probably be calculated, including the speed difference using rod end/head end compensation, but gonna need some more info on pressures, etc. Fluids don't compress, so GPM into a specific volume/cross sectional area should tell you how fast somethin's gotta move. I'm not quite sure "regenerative" is the correct word for that diagram, though. I'm hoping that animation is over-simplified, because what I see would ALWAYS have pressure on the Rod end, and only bleed the head end to tank on retract. A larger port on the head end would certainly allow the head end to bleed to tank faster, and this is pretty much common practice because of the difference in volume on each end of a cylinder. Pressurizing the head end would indeed push the smaller CSA (cross sectional area) of the rod end if there was some relief to tank, but I'm not quite sure I buy into it making any significant contribution by pushing the oil right back into the same line. Once it contacts anything and the pressures equalize on both sides of the piston, that cylinder cannot move without bleeding volume to tank from the rod end. I think I'm not seeing all of the circuit for the 'regenerative' function. Perhaps a pressure relief and a check built into the valve? If that's the case, there's always going to be some pressure on the rod end in that diagram, meaning loss of efficiency on the head end in the name of faster extend speed (until it hits the wood). I've seen a lotta things done with hydraulics working around large rolling mills (steel and aluminum) as well as paper machines, some cylinders designed to put out millions of pounds of force, but with a stroke less than an inch long, some with nearly 30 foot rods. It always comes back to the same calculation, though that you can have more force extending, and more velocity retracting. Some of them really made me scratch my head. But hydraulics is not unlike electricity, and I do understand both will take the path of least resistance. I've done my share of regulating hydraulics and controlling the pumps with electricity. Didn't have a choice but to understand the hydraulic side. Return to tank is about as fast and least resistant as it can get. The larger the line (and valve port), the higher the return capacity. I've seen many applications with larger lines on the head end of the cylinder, simply because of the need for higher flow on that end. Get it large enough, then back-pressure of the return becomes negligible with respect to volume from the pump. What I see in that diagram is waiting to stall on a hard piece of wood, and the advertised tonnage of pressure is probably based on cylinder size only. Like I said, though, I think it may be over simplified.

Regeneration is the word used in hydraulics literature every where and there are many variations on the circuit designs. The force and travel speed calculations are straight forward based on pump pressure and flow, cylinder volume, and piston working areas. In a regenerative circuit of this type when there is a load on the rod end both rod and head end are under pressure and in opposing directions. The net force on the rod is determined by the difference in the piston working areas on the two ends. And because the piston working area of the base end is always larger than the rod end there is always a net force outward. That is simple everyday high school physics.

In this particular log splitter valve the extend end of the spool has two positions. In the fully shifted position the regen circuit is open and rod end oil is being redirected to the base end - the rod moves at increased speed but greatly reduced force. When the wedge hits the log in this mode the cylinder can and often does stall because the net force being generated is insufficient to split the log. At that point the operator simply allows the lever to drop back to the second position on the spool where the regen circuit is closed and rod end oil is directed to the tank outlet as usual. Now the full hydraulic pressure of the cylinder base end is being applied to the rod and the wedge proceeds into the log.

Its a simple, economical, reliable, and easy to use mechanism and works as advertised.

Dan

 

[Old_Paint]

In this particular log splitter valve the extend end of the spool has two positions. In the fully shifted position the regen circuit is open and rod end oil is being redirected to the base end - the rod moves at increased speed but greatly reduced force. When the wedge hits the log in this mode the cylinder can and often does stall because the net force being generated is insufficient to split the log. At that point the operator simply allows the lever to drop back to the second position on the spool where the regen circuit is closed and rod end oil is directed to the tank outlet as usual. Now the full hydraulic pressure of the cylinder base end is being applied to the rod and the wedge proceeds into the log.

Dan

That's the part I wasn't seeing in your diagram, the second stage of the valve, which is what elicited my comment. Now I understand you were just posting the primary circuit. I think we're in agreement about the force of the rod end fighting the head end unless the rod end is vented to tank after contact. A cylinder with a large ratio of head-end CSA to Rod-End CSA will certainly have greater force, and log splitter cylinders typically have at least a 2:1 ratio, some as high as 4:1. Small cylinders like the ones on the FELS where the rod is not much smaller than the bore would stall very quickly. That it will move the rod with nothing in front of it, no doubt, because as you point out, the rod moving out makes more room for hydraulic fluid. The volume is what moves it, not the pressure, but the pressure is certainly what will determine the force required to move the rod. Pump volume is still the deciding factor in moving speed. I'm fairly certain there are systems out there that sense stall pressure on the incoming pressure at the valve, and pop the return to tank valve on the rod end, which would in essence make the loss of speed on the extend stroke unnoticeable. The force from the cylinder wouldn't be, though.

 

[TheOldHokie]

That's the part I wasn't seeing in your diagram, the second stage of the valve, which is what elicited my comment. Now I understand you were just posting the primary circuit. I think we're in agreement about the force of the rod end fighting the head end unless the rod end is vented to tank after contact. A cylinder with a largepl ratio of head-end CSA to Rod-End CSA will certainly have greater force, and log splitter cylinders typically have at least a 2:1 ratio, some as high as 4:1. Small cylinders like the ones on the FELS where the rod is not much smaller than the bore would stall very quickly. That it will move the rod with nothing in front of it, no doubt, because as you point out, the rod moving out makes more room for hydraulic fluid. The volume is what moves it, not the pressure, but the pressure is certainly what will determine the force required to move the rod. Pump volume is still the deciding factor in moving speed. I'm fairly certain there are systems out there that sense stall pressure on the incoming pressure at the valve, and pop the return to tank valve on the rod end, which would in essence make the loss of speed on the extend stroke unnoticeable. The force from the cylinder wouldn't be, though.

Yes, there are competing forces acting on the rod but I think you have the physics backwards. A pressure imbalance (force) is required to move the rod which results in a volume change. Without a pressure differential the rod does not move and volume does not change. That's a fundamental principle of hydraulics and more generally Newtonian mechanics (e.g. physics).

Quantifying the effect lets take my splitter as an example. The cylinder has a 4" bore and 2" rod.

Assuming a system relief pressure P of 2000 PSI we get:

Working area of the base end = Abase = 4pi
Working area of the rod end = Arod = (4pi - 1pi) = 3pi

Similarly the forces are :

Fbase = P x Abase = 8000 x pi = 25,132 pounds
Frod = P x Arod = 6000 x pi = 18, 850 pounds

In "normal " mode Frod is essentially zero and we get a maximum splitting force of Fbase = 25, 132 pounds.
In "regen" mode the net force is (Fbase - Frod) = (25,132 - 18,850) = 6, 282 pounds

So the regen circuit reduces the maximum splitting force from roughly 12 tons to 3 tons. Quite a hit but since we only use it to speed up travel when the rod is unloaded and then revert to normal mode for the actual split its a non-issue in this application.

We could if we wished similarly calculate the increase in the in flow rate at the base end and the corresponding increase in rod velocity that regen produces but I will leave that for another day.

Dan

 

[GreensvilleJay]

From the description of how this 'regen' valve works, it sounds like a 'bodge' to fix an underdesigned splitter, as it sacrifices power for speed. If you need xx tons of force for yy seconds of time, you just 'do the math', select pump, hose, valves, etc. to do the job. Now it may be 'they' decided spending an extra $20 on the regen valve instead of $100 for a bigger pump was a solution,even though the system traded off power for speed. It's a compromise someone decided was right for them.

 

[TheOldHokie]

From the description of how this 'regen' valve works, it sounds like a 'bodge' to fix an underdesigned splitter, as it sacrifices power for speed. If you need xx tons of force for yy seconds of time, you just 'do the math', select pump, hose, valves, etc. to do the job. Now it may be 'they' decided spending an extra $20 on the regen valve instead of $100 for a bigger pump was a solution,even though the system traded off power for speed. It's a compromise someone decided was right for them.

Subject of this thread is 3pt log splitters and that is what we have been discussing. These splitters do not have a pump - they run off the tractor hydraulics.

In this application regeneration does not sacrifice force - you have the full splitting force of whatever pressure your tractor hydraulic system and the log splitter cylinder can muster. In my case that is a 4" cylinder and 2000 PSI tractor pressure which generates 12T of splitting force.

Regeneration is not a "bodge" - it is a well understood and commonly used hydraulic circuit used to speed up cylinder actuation under no or low load conditions. It is used in many implement valves including Kubota loaders and quite likely present on your BX23-S.

Dan

 

[Old_Paint]

Actually, I'm finding far fewer 'self-contained' 3PH splitters than those that use the tractor hydraulics. They seem to be quite expensive when you do find them, albeit, typically European manufacture. I'm sure the pump and reservoir are the primary reasons for additional cost.

Bottom line, regardless of how fast it is, I'd prefer the splitter not share my tractor hydraulics. 3PH splitters tend to be left outdoors (because they're huge and take up a lot of space), and hydraulic oils are typically water magnets. Self-contained (drive-shaft driven) 3PH units solve the issue of pumping watery sludge from the cylinder into your tractor, albeit, they still do nothing about the watery sludge that they pump through themselves. They have to be covered to prevent this problem, and no way would I ever hook one up without an external filter in the return line. What you save by getting one without a pump will likely cost you 5-10 times more when the crud that comes out of it goes through your hydrostatic system. You'll get better power and speed from one with it's own pump and reservoir, and a LOT of insurance that it won't hurt your tractor.

All that said, the gas powered units are typically fairly light, have their own chassis with wheels, and typically cost a little less. The main detractor that I see about them is that it's another engine that MUST have all fuel removed from it before storage, another engine to PM, and all the other bothers that go with small gasoline powered engines. Gasoline powered versus direct connect to the tractor hydraulics is a no-brainer to me. Cost of PTO driven versus gas engine powered, and a place to store something with an engine on it are the final trade-off considerations.

Would love to hear other's experiences with the gas-powered ones, including annual/periodic maintenance and any mechanical/lubrication anecdotes as well.

 

[Old_Paint]

Subject of this thread is 3pt log splitters and that is what we have been discussing. These splitters do not have a pump - they run off the tractor hydraulics.

In this application regeneration does not sacrifice force - you have the full splitting force of whatever pressure your tractor hydraulic system and the log splitter cylinder can muster. In my case that is a 4" cylinder and 2000 PSI tractor pressure which generates 12T of splitting force.

Regeneration is not a "bodge" - it is a well understood and commonly used hydraulic circuit used to speed up cylinder actuation under no or low load conditions. It is used in many implement valves including Kubota loaders and quite likely present on your BX23-S.

Dan

Would you not agree that as the ratio of rod-end CSA and head-end CSA decreases, the benefit of (what I would have called "recovery") regeneration will diminish, particularly on the extend mode of the cylinder? There's got to be enough flow coming from the rod end to make a significant difference in volume change on the head end to truly affect speed. If the rod end volume is much smaller, then obviously, the volume change with respect to displacement is a lot smaller. That's just a proportional relationship. One of your posts said 4" cylinder with 2" rod, but you did the math for a 1" rod. 1" rod in a 4" cylinder would be a 4:3 ratio of volume. 4" cylinder with 2" rod would be a 4:2 ratio. A very significant difference that will affect a regenerative circuit's performance.