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B7500 and a Log splitter

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Duane
Join Date: Feb 2002
Posts: 53 Western PA
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2002-02-10          35465

I was planning on building a 3pt hitch log splitter for my B7500. I had originally planned on running the splitter off the tractor hydraulics and using the loader valve for control, but now am questioning whether or not those hyraulics are powerful enough. The operator's manual shows the power steering pump capacity as being 2.6 gpm, while the 3P (which I assume is the 3pt hitch) has a flow capacity of 4.4 gpm. First of all, aren't the 3pt hitch, power steering, and loader hydraulics run off the same pump? And that pump being located on the back of the injector pump? If so, how is there different flow capacities? Most log splitters I have seen have at least 11 gpm flow for say a 20 or 22 ton splitter. I was thinking that maybe a PTO pump would be the way to go. Which brings me to my second question... if I go with a PTO pump, how big of a pump and what size of a ram should I buy to maximize splitting force and speed? The tractor has 16 PTO horsepower, and runs at either 540 or 960 rpm. Any help in this matter would be greatly appreciated. Thanks.
By the way, this board brought me to the purchase of my B7500 a year and a half ago, which now has 165 hours on it... best purchase I have ever made... thankyou.


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Peters
Join Date: Feb 2002
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2002-02-10          35468

The power steering pump and the general hydrallic pump for implements are split on most new tractors. This is to prevent the power steering from being effected by the loads placed on the system by the implements. Ie if you have a full load in the bucket lifting it you do not want the power steering to suddenly get heavy.
Smaller tractors do not have that large of an oil reservoir. Log splitters require a lot of force and therefore a large cylinder. This then requires a lot oil. It is better to have a PTO pump.
If you are going to build your own system I think it is nicer to have a vertical unit so you don't have to lift the blocks onto the rail. I am not sure that you can do this with a 3 pt arrangement.
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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2002-02-11          35473

I imagine that most PTO pump manufacturers publish recommended PTO HP ranges for their pumps. I'd probably look for as big of one as I could find that is recommended for 16 HP.

I think the tractor hydraulics would make for a very slow splitter. Peter's comment about reservoir size should be noted. Splitter cylinders end to be large diameter and long. They contain a lot of oil when extended. All the oil goes back in the reservoir when they're retracted. It's possible that a small tractor reservoir would go from too full to too low during operation. Another small reservoir problem is that if the work is heavy, the oil may overheat.

My Ford 1710 PS and remotes work off a single pump. There is a priority valve that robs flow from the remotes to feed the PS as required. Under heavy loads, the loader slows down when steering. Some of the JD 4000-series compacts have two pumps. However, they have a design where flow from the PS pump is combined with the remote pump during heavy remote use. The idea is that flow decreases at high pressures, and hydraulic operations slow under heavy loads. The design speeds up heavy work, but at the expense of PS. I understand the design, but I'm not sure I'd like to give up PS for more loader speed. Turning with a heavy loader load seems exactly when you want PS.
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Duane
Join Date: Feb 2002
Posts: 53 Western PA
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2002-02-11          35477

OK, you guys sold me on the PTO setup, and it makes perfect sense that if you pump enough oil out of the reservior to fill a 4" or 5" diameter cylinder 24" long you would end up nearly running the thing dry. Am I correct in saying that all the hydraulics on a B7500 hydro run out of the same reservior? Just wondering. Question: Northern tool has a pump that runs 11.4 gpm @ 540 rpm, and I was wondering if it would be better to get that pump and run the PTO on the 1000 rpm setting but throttle the engine down to 1436 rpm to get the 540 on the PTO. Seems like it would be better if I didn't have to have the tractor tached out the whole time. Only thing is, does the tractor have enough hp at 1436 rpm. None of the product descriptions have any hp ratings, and I have never seen a hp curve chart for a B7500. Only thing I can go by is a complete log splitter Northern has... it has 11 gpm pump with only 5 hp gas engine... seems like i should have at least 5 hp at 1436 rpm. Probably could go with even a bigger pump... Hey I don't know.. I am just guessing here... maybe you all could share some engineering knowledge with me about all this. I don't want to end up with a splitter that has a 2 minute cycle time or something. lol. ....

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Duane
Join Date: Feb 2002
Posts: 53 Western PA
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2002-02-11          35478

OK, here's one more factor to throw in... what about system pressure? How do you determine what it's gonna be? Maybe I am getting in over my head here with technical stuff... Just found a site on the net that gives alot of info about fluid power... It says that "For every 1hp of drive, 1gpm @1500 psi can be achieved." I see Northern has a 30 ton logsplitter with 22gpm pump, and 13 hp engine. According to the 1hp drive=1gpm@1500psi theory, they should only get 13 gpm @1500psi... soes this mean the thier operating pressure is lower on this splitter than 1500psi? If I could run a 30 ton splitter off my little tractor I'd be as happy as a clam as I generally use about 8 cords of wood per year. Splitting by hand has become tiresome. PLease help. ....

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Duane
Join Date: Feb 2002
Posts: 53 Western PA
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2002-02-11          35479

Alright, my brain is frying... One more stupid question, then I'll quit. I see most of the log splitters have 2 stage pumps... for quick movement of the ram under no load situations. PTO pumps do not appear to have that option... will this drastically affect the speed of my splitter? Perhaps having a 2 stage pump is what allows you to run these big pumps with what seems like relatively small engines? ....

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Murf
Join Date: Dec 1999
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2002-02-11          35488

Actually Duane I hate to waste a good brain fry, but your a little off on one point, filling the cylinder doesn't take as much fluid as you think. The reason is that the cylinder is not empty to start with. there are two volumes to a hydraulic (or air) two way cylinder, one each side of the piston, to allow two direction force. The difference between the two sides is equal to the displacement of the ROD only. As an example, if you have a splitter with a 4" x 24" cylinder with a 2" cylinder rod. the fluid required to move the cylinder full stroke is not (for ease of explanation) NOT 4" bore x 24" of stroke worth of fluid, it is 4" of bore minus the 2" of rod x 24" of stroke. Or in real numbers, it is not, 4" x 24" or 1206.3715789785601 cubic inches, it is 4" - 2" x 24" or 904.7786842339201 cubic inches because 2" x 24" or 301.59289474464 cubic inches of displacement is created by the cylinder rod itself which is inside the cylinder when it is in the retracted position. Clear as mud, huh? The Tylenol is on me, LOL. Best of luck. ....

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Duane
Join Date: Feb 2002
Posts: 53 Western PA
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2002-02-11          35489

Actually murf, that makes perfect sense... I told you my brain was fried. I would still like some hard numbers on pump and ram size to fit my tractor though. I mentioned earlier that I would prefer to run the tractor at lower throttle other than wide open... I have rethought that... the bigger, stronger, and faster the log splitter, the better. Like I said, I generally burn 8 chord per year myself, not to mention there are 3 other households in my family who would benefit from this thing. ....

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John Mc
Join Date: Feb 2002
Posts: 98 Vermont
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2002-02-11          35503

Duane -

Just a thought... I don't own a logsplitter (yet), but I've been following a lot of threads on them, here and on other boards. There are a lot of arguments being made for a stand alone splitter (not driven by tractor hydraulics or PTO)... and the more wood you split, the more sense those arguments seem to make. The main point is: do you want to tie up your tractor in one place while you split the wood? You could be hauling in more logs, holding a FEL full of logs at a convenient height to feed the splitter, hauling off split wood, etc. all while leaving your splitter set up (and running, if you've got some help).

Not trying to talk you out of a good project... building one sounds like fun. But perhaps you might want to design it with an easy conversion in mind to a separate gas engine powered unit, just so your options are open down the road. ....

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Duane
Join Date: Feb 2002
Posts: 53 Western PA
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2002-02-11          35508

John,

Those are very good points, and I have already considered them. I cut everything up and haul it to my place here where I unload into a lean-to shed on my garage and later stack it. My point is, that when I am ready to split, I am generally not doing anything else... except stacking the wood 5 feet from where I am splitting.

The splitter I am going to build will be a trailer type, that can go horizontal or vertical. Got it all figured out how to build, just need some numbers. And yes, it is going to be a fun project... Everytime I build something like this I generally go a little overkill and make things a bit stronger than they need to be... kind of like Tim Allen on Tool Time. lol ....

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2002-02-12          35511

Yikes and Fried! I guess a 2-stage pump refers to a stand-alone splitter. I'm not sure what such a thing is in this context or what it does. I could use some straightening out here, but the ways I imagine such a thing working would seem to help high load speed rather than low load speed.

Big standalones do seem to have smaller engines than tractors. A reason is that a specialized system can be optimized for a single type operation. A stand alone doesn't have to run a TX/PTO/Clutch, or an alternator etc.. On the other hand, it's easy to get 'bogged 'n fried' by specs and features. They are advertising after all. Tons or gpm's may not be the same.

Murf is right about volume (good to have your comments as always). Never the less, operation of big cylinders with small TX/DIFF reservoirs will produce large swings in the level. After topping up the oil when first connecting, a splitter cylinder may have to be positioned mid-way prior to removal to keep the right TX oil level. I think heat is a more important issue. I can't remember the rule of thumb that relates flow to reservoir size.

When operating a splitter from tractor hydraulics, the tractor’s system relief valve setting determines pressure. Some compact system pressures are on the low side of recommendations for splitters. I think the release detend on a splitter valve operates on pressure. Some valve may not work on low-pressure tractor hydraulics. Something that would definitely speed up operation is a regenerative circuit in the splitter valve retract circuit. I don't know if they are common features in splitter valves.

The hook-up into tractor hydraulics also is something to consider. If the splitter is run from typical auxiliary system ports, then the 3ph is behind the splitter valve. In such a case, the splitter valve should be a power-beyond type, or the valve's exhaust galley should be rated for system pressure. If the 3ph lifts a heavy load, the entire pressure line, including SCV's, sees high pressure.
....

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Peters
Join Date: Feb 2002
Posts: 3034 Northern AL
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2002-02-12          35513

I'm sorry I was not thinking about the volume displacement correctly. The only time you would need to worry would be when the cylinder is new.
I hate to muddy a good plan but I have a log splitter in the barn which has not been used since I got it. It came with the property. I currently am running a ground based heat pump with pellet back up.
The splitter has a PTO pump and a large beam. I have never had it on the tractor so I am not sure it will fit on the small one. I can check and would be will into part with it for around the same price as a new remote unit.
I am in northern Alabama. ....

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Duane
Join Date: Feb 2002
Posts: 53 Western PA
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2002-02-12          35517

Peters,

Northern Alabama!! That's a ways away from Northwestern PA. Besides, I would like to build a trailer type... that way I could haul it out to my dad's behind the truck, and he could then hook it up to his tractor. I have been looking and looking for information on how much system pressure splitters need, and so far nothing... all I have found out so far is that I can achieve 16 gpm at 1500 psi with my pto... but I don't think 1500 psi is enough... i imagine that if I lessen the gpm, the pressure would increase... but then again, I know nothing about hydraulics... Then there is the factor of ram size... geesh... basically I am still looking for someone to give me a combination of pump size, ram size, and what pressure it will all be operating at with the 16 pto hp on my tractor. ....

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2002-02-13          35553

There's a long discussion about building a splitter at Yesterday's Tractors.

http://www.ytmag.com/toolt/messages/6419.html

I didn't scan through it, so I don't know if any of it gets into the hydraulics.

Another approach may be to just not struggle with the specs and have faith that the tractor will run a splitter at some sort of useful capacity. A dealer should be able to identify the largest PTO pump recommended for the tractor, and virtually any pump is capable of producing enough pressure to run a splitter. Virtually any splitter valve is capable of being connected to any pump.

Almost anything will work. It's mostly a question of speed. I've heard people say a splitter works fine for them running from 8 gpm tractor hydraulics. I've also heard of people unhappy with the performance from larger pumps.

One thing about the specs: I think most tractor pump gpm ratings are unloaded and at PTO speed. No load pressures are maybe a couple hundred lbs.. It is true that flow decreases as a pump builds pressure. It's also true that a splitter spends more time operating under no-load pressures than max pressure. Pumps deliver pressure as demanded. They build pressure to a point where the load starts moving or a relief valve opens. A splitter would spend only brief periods operating at max pressure, considerable time operating at moderate pressure and a lot of time at no load as the cylinder retracts.

I think a safe conclusion is that it's really difficult to calculate from specs how fast a splitter would operate. However, max pressures and splitter forces could be calculated. Whether max forces would be required depend on the wood to be split. Again, no simple answers. The bright spot in all this is that if the tractor is capable of running a 16 gpm pump, it almost certainly would be capable of doing useful work with a splitter. Of course, the 3ph may have trouble lifting the reservoir required. I'm not entirely serious here, but exact answers are often elusive.
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MarkS
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2002-02-13          35569

I own a TC40D and I am running a log splitter (4" bore 24" stroke)off from the 3rd service hydraulics. The TC40D has about 9.8GPM no load flow rate. ITs not super fast, but its also not so slow that it drives you crazy (Its a hell of alot easier than and axe or a maul). Previous to the TC40 I owned a Cub Cadet 7232 and I belive the pump flowed somewhere between 5 and 6 GPM no load. It was too slow and was very frustrating. IF possible I would make sure I had a pump that flowed at least 10GPM. My 2C worth. ....

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Duane
Join Date: Feb 2002
Posts: 53 Western PA
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2002-02-13          35573

Mark, your TC40d has about twice the power of my little b7500... I imagine you have no trouble producing the psi needed to run a splitter without stalling the tractor... as most run about 2500 psi I think. Self contained units with relatively small gas engines are able to produce the high pressure because of a 2 stage pump which drastically reduces the gpm, and drastically increases psi under heavy load. Kind of like putting your tractor in low range first gear... it lugs alot less on the engine. I am worried that if I don't find a two stage pto pump I could possibly stall the tractor trying to run 15 or 18 gpm when I hit a big knot in the log. Then again... I might be all wet... which is usually the case. I have a question for you all... is there such a thing as a two stage control valve? I imagine that what makes a 2 stage pump a 2 stage, is a valve of some sort in the pump... I wonder why that vavling couldn't be put into teh control valve for the cylinder... once again, I might be all wet. Let me know. ....

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2002-02-14          35590

I was hoping that somebody like Mark would respond and provide actual experience. I don't have actual experience, because my dealer told me I probably wouldn't be happy with the speed from my 8.1 gpm tractor system when I looked at a used splitter. I didn't want to buy a PTO pump just for a splitter and never looked further.

Sorry this is rather long. Please don't take it as a statement of any particular expertise. Hope it helps a bit. I'll note some general stuff about hydraulics. Pumps in ag operations come in a number of types--two kinds of gear pumps, vane, axial piston and radial piston. Most likely you'll encounter gear pumps, but piston types are around. Most importantly, almost all gear pumps are capable of producing around 4,000 lbs. intermittent pressures. Piston pumps are generally capable of higher pressures. Almost any ordinary ag pump is capable of intermittent pressures far in excess of typical system pressures found in compact tractors.

Intermittent pressure ratings are the most important for ag operations, but pumps also have continuous ratings (it's mostly a heat problem). I noted that flow is usually rated at no-load PTO rpm. Volumetric efficiency is another rating, which is the difference between high and low-pressure flows. Ratings from 70% - 90% are typical. There also are mechanical and overall efficiency ratings. I don't know what a 2-stage pump is. What ever it is, I don't believe they're common in ag applications.

The system pressure is set by a relief valve and has nothing directly to do with the pump. A system relief valve is a return line to the reservoir that is blocked by a spring-loaded ball valve. The valve opens when pressure overcomes the spring, and the line diverts flow from the high-pressure line through the relief valve line. Relief valve pressures usually are adjustable by placing shims behind the spring. System relief valves don't create high pressures, they bleed-off excessively high pressures. Most SCV's and 3ph's also have relief valves, but these generally protect against shock loads when control valves are in operation.

An important idea in hydraulics is that pumps create flow, not pressure. Loads create pressures. Another idea is that force and speed are inversely related. A small engine with a small pump can lift huge loads by using large cylinders, and the max pump pressure remains the same (pressures can't exceed the relief valve setting). However, the operation is slow because a larger volume oil must be pumped, and there are volumetric and other efficiency losses. Again, pressure isn't determined by the pump, pressures result from the combination of load and cylinder size. A pump can't develop higher pressure when a load starts moving or the relief valve opens.

A small engine can operate large pumps with moderate loads. If a load is excessive, the engine doesn't stall because the relief valve opens. As above, with larger cylinders, a load would no longer be excessive. It is true that an engine could stall with an excessively high relief pressure setting, but that's really the purpose of a system relief valve. It limits requirements to what are manageable by an engine. Hydraulic lines, components etc. generally are capable of withstanding the max pressures of any ag pump.

There's nothing much magic about hydraulics. It's just a way of getting work out of an engine, and its also provides a convenient way to spread high work loads over longer times. Most tractor hydraulic systems are relatively small for their engines, because it's not desirable for the hydraulics to grab too much available HP. The advantage of a PTO pump is that pretty much the entire engine output can be put into the hydraulics.
....

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Duane
Join Date: Feb 2002
Posts: 53 Western PA
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2002-02-14          35602

Excellent description of hydraulics tomg... it's true that there is nothing much magic about hydraulics, but it can be confusing when you dive headfirst into it without knowing anything to begin with. I think I am going to go with a 20gpm pto pump and a 5" cylinder and hope my 16 pto hp is enough. If any one thinks this is wrong, please let me know. Thanks. ....

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Duane
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Posts: 53 Western PA
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2002-02-14          35605

Well fellas, I think I figured it out. It's a good thing I haven't bought that 20gpm pump yet. I found a formula in a Northern catalog...

"hp required = flow rate(gpm) x system pressure(psi) / 1714 x %pump effeciency"

My previous post when I said I'd get a 21 gpm pump would only yield 1175 psi before I stalled the engine. I am pretty sure log splitters run higher pressure than that. And to actually achieve 2500 psi would require 34 hp. According to the formula, the most gpm I could run would be 10 gpm. That's with a straight one stage pump. The northern catalog says that two stage pumps require about 1/4 the hp of regular pumps. SO unless I find a 2 stage pto pump, which I do not think exists, I am going to scrap the whole idea. Heck, I can buy a complete 20 ton splitter that runs 10 gpm for 800 bucks. The only way it would be worth it to build one is if I could build like a 30 or 35 ton splitter.... those run about 2k That would be more cost effective. ....

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Duane
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Posts: 53 Western PA
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2002-02-14          35606

For those of you who don't know how a 2 stage pump works, or never heard of one, I am posting the paragraph from the Northern Catalog describing one.

In one housing there are two pump sections, one small and the other section three times larger. The flows of both pump sections combine to produce high flow at low pressure. When the load increases above the unloader valve setting, oil is diverted from the large pump section so that only a small section is generating flow. In this situation the flow is approx 1/4 of full capacity with pressures up to maximum. Operation will continue until load decreases below the unloader valve setting, and then the pump shifts back smoothly into high capacity/low pressure mode."

Sort of like having a high and low range. ....

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TomG
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2002-02-15          35616

I figured it would be something like that. The design may have some advantage for a single specialized operation like splitting, but such things usually have downsides for general applications.

In effect, the design addresses the problem that you can't have both high flow and high pressure run from a small engine, but both are needed for a splitter--even if high pressures are needed for only brief periods. Flow at a given pressure is a measure of work, and only an engine can do so much work in a given time. An alternative is to use a high flow pump with bigger cylinders, because then loads would move with less pump pressure. Anyway, it's no trick to design pumps that have good flow, produce high pressure and have decent volumetric efficiency in a single stage. Good pumps are expensive though, and so are large cylinders. If I were guessing, I might suspect that the 2-stage idea is just an less expensive way to get work with specialized requirements done.

....

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TomG
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2002-02-15          35617

Duane: I had to take a net break and provide some convalescing services to my dog who is recovering from surgery. I have to wait on him for a change so he won't sit in the snow and get his bandages wet. I just wanted to say that it sounds like you're doing a good job of coming to grips with this hydraulics stuff. It's especially good to be able to put some number to this relationship between volume/pressure (work) and your particular tractor. Having been forced to think this thing through, I've learned a bit as well. ....

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Duane
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Posts: 53 Western PA
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2002-02-15          35620

Thankyou for the compliment tomg. I wanted to tell you that before I give up making a splitter I have one more brain storm to try. More than anything I want to build one just for the fun of it, so I am giong to keep thinking on this. SO here's my idea.

Buy a 2 stage pump that runs 22 gpm and a used 1:4 ratio gear box off an old 3 pt hitch mower deck. The gear box would allow me to obtain the 3600 rpm required for maximum flow on the pump while running the pto at 1000rpm. A straight pump that size (running 85% efeciency) would require 38 hp, but a 2 stage should require only about 10hp. I think the pto hp ratinge on my tractor are given of the 540 rpm setting, but I imagine the hp doesnt' drop below 10 when using the 1000 rpm setting. Using the tractor on 1000 rpm pto setting, I should be able to run the pump at maximum flow when the engine runs about 2400rpm... not quite tached out. Add a 5" ram and I should have one hell of a log splitter. Not that anyone NEEDS a slitter that big, but it would be fun to build.

I see that northern has a 30 ton splitter with a 5" ram and 22gpm pump... it has a 13 hp honda. Is there any way to know how much pto hp my tractor has on the 1000 rpm setting? I am not sure how hp and torque change on pto's as you switch gears like that. It would be nice to know for sure if I do indeed have enough hp to run that particular setup. ....

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Peters
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2002-02-15          35624

Ok
This is my theory and it is mine.(Monty Pithonism)
Could you not buy two PTO pumps with the different pump rates and then value them together to you what is available on the commerical 10 hp unit?
Alternatively could you use a tractor hook to the hydralic pump for the high pressure low volume and the PTO pump to give you the low pressure high volume.
This would be complicated plumping but as you what a high performance rig.
Running the high volume pump with the gear box is not going to gain you HP with the shaft speed increase. You still need the 38HP to get full pressure and volume from the high volume pump.
Splitting the load betwween 2 pumps may get you the desired effect. ....

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Duane
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2002-02-15          35625

I think you may have misunderstood me peters, about the hp thing anyways. The 2 stage 22gpm pump does not always flow at 22gpm. As soon as the pressure goes above a certain psi, (lets say 750 psi as an example) the pump then switches off the large section of the pump reducing the gallon per minute flow, and hence creating the ability of the system to more easily produce the necessary psi (lets say 2500 psi as an example). From what I have read, when the pump swithes to low flow, it runs 1/4 the gpm rated of the pump. Plug that into the equation for the 22gpm pump...


up to the point when the system builds 750 psi, the max hp required should be:

hp required = (22gpm x 750psi)/(1714 x .85)
hp required = 11.3 hp


Now, after the point when the system is past 750 psi, and the large section of the pump has stopped pumping the max flow should be:

22gpm x 1/4 = 5.5 gpm


And the max hp needed to pressurize the system to the relief valve setting of 2500 psi is:

required hp = (5.5gpm x 2500psi)/(1714 x .85)
required hp = 9.4 hp

Now, the 750psi number I used for the cutoff is just my guess, and the .85 is the effeciency of the pump I am looking at... but you get the jist of it. I reckon your idea of running 2 pto pumps or one pto pump and the tractor hydraulics would work though... same basic principle, just a bit more work. My only question about the hp on my tractor pto was whether or not it changes when you swithch from 540 to 1000 rpm. The engine rpm remains the same, just the pto rpm changes. I think... remember I am thinking now, that the hp would stay the same, but torque would be reduced. That is just a thought, and it's probably wrong. Anyways, if anyone has any input on my idea let me know. The more info I have the better. thanks everybody. ....

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Murf
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2002-02-15          35627

The idea of two pumps in a wonderful notion. Problem is, unfortunately, hydraulic fluid, much like electricity or water, will always take the path of least resistance. So without check valves, etc., to prevent back-flow, the high volume pump would also pump fluid into the output side of the low flow pump until a pressure balance is reached, then it would reverse and the higher pressure pump would try to turn the other pump backwards. Not a good situation. If this splitter must operate at high speed, then I would suggest a high volume used pump, like those found on redi-mix concrete trucks, this will give great volume at decent pressures.

Other than that the only flaw I can find in any of this excellent brain-storming is I think loading / unloading time has been forgotten. It doesn't much matter if the splitter can cycle in less than 15 seconds if it takes 30 seconds to get the last piece out and another piece back in ready to split. Real world operating needs and conditions are usually very different from hypothetical ones.

Best of luck. ....

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Peters
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2002-02-15          35632

OK Murf I agree that I don't have all the answers, but this is basically what Duane described is on the stand alone splitters. The problems is I am not familiar enough with the hydrallic valves etc.
Basiclly it would require the high volume pump to pump to a certain pressure, for example 1000 psi and then open a valve and dump the flow to recycle, while closing the out flow to the pressure side. The high pressure/low volume pump would finished to 3000 psi. Once the leaver is reversed the two pumps would kick back together.
You might be able to do this with pressure controllable check valves. ....

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Peters
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2002-02-15          35633

Come to think about it, it might be better to modify a two stage pump to accomidate the PTO drive?
There are a number of pumps.
Incidently the Land tracks appear to have thought of the problem already and incorporated 2 stage pumps in the tractorss www.mtrac.com/LANDTRAC360.html
Pumps
www.marzocchi.com/pumps/products/catalog/hilo/default.asp
www.baileynet.com look at the Haldex Barnes pumps (250012?)
Sorry Duane I bet you thought this post had run the course.
....


Link:   two stage hydraulic pumps

 
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Duane
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2002-02-15          35638

Well now, I just got an email from a fella who has built some log splitters in his day... He has yet another view on things. He claims that 2 stage pumps are for TOYS. lol I don't know what to think anymore. :) He made a good point though, that If I ran a 1 stage 16 gpm pump, I could hold 1500 psi without bogging the engine... and that once the pressure would rise above that towards the 2500 mark, the tractor would just bog down to around 1600 rpms, where the pump flow would be reduced to about 10 gpm at 2500 psi. 10 gallons at 2600 psi requires 16 hp... the rated hp of my pto... makes sense to me other than the 16 hp rating is with the engine running at 2600 rpm, not 1600. I don't know how much difference there is in hp between those two rpms, or how much it really matters... uh oh... i feel another brain fry coming on! ....

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Peters
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2002-02-15          35641

From the little I looked at in the two stage pump spec. pages, I would say that there are two quality of pumps. Like the pumps for the pressure washers there is the low end price leader and the more expensive high quality pumps.
From what I saw you can size the pumps to your HP and volumes just like the PTO pumps.
I am sure it will clean out the piggy bank to get the highest quality pumps. ....

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Duane
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2002-02-16          35647

ok, I think I've made up my mind. I think. Maybe. What that guy told me about using a 1 stage 16 gpm pump makes more and more sense to me the more I think about it: As the psi increases, gpm flow must be reduced to a point where the tractor has enough hp to keep running the pump... That would be somewhere between 8 and 10 gpm, and as the tractor boggs down, hp goes down but torque goes up... I think it's the way to go. Saves trying to couple a gear box to the 2 stage pump, not to mention it uses fewer moving parts... no pto shaft, no gear box ... less stuff to break. Any one seen a 16 gpm pto pump anywhere? I have seen 11, 22 and 40 gpm from Northern, but so far that's it. Let me know if you come across anything. ....

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TomG
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2002-02-16          35650

Yikes--lot of traffic here and that's good!

Yep, Murf's usual practical side comes through to keep, at least me, from complete self-indulgence at armchair theorizing. Cycle times faster than logs can be placed in a splitter might be something that could be sold to the government but probably not elsewhere.

I think my elegant (although granted arm-chair) solution for this might be a variable displacement axial flow pump. These are the same type pumps found in most HST's, and they even might be available as a standard 540-rpm PTO pump. The advantage of such a pump is that the flows are continuously variable (to a max) at given pressures.

I imagine that it would be an interesting little trick to design a feedback system that worked on pressure so the pump's swash plate angle would change with pressure increases to reduce the volume. My impression is that the 2-stage or two pump idea might work pretty well for log splitting, where high pressures are required only for brief moments and the accompanying large decreases in speeds aren't important. I don't think those characteristics would be desirable for operations like running a back-hoe.

Duane: Since you originally described yourself as knowing nothing about hydraulics, I wonder if you've come to grips with some of the tractor basics like the differences between open and closed systems or normal and power-beyond valves. There is a bunch of stuff in the archives.
....

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Duane
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2002-02-17          35669

No Tom I am not familiar with the different kind of systems or valves. I know how to set up the system on a log splitter and that's about it. I searched a bit for some info here at ctb but couldn't seem to find what I was looking for... must not have been looking in the right place. I have become intersested in hydraulics in general now, and will eventually figure it out... hopefully. Found some handy calculators at

http://www.baumhydraulics.com/calculators.htm

Oh, and I found out that Prince makes a 17.1 gpm (max pressure 2250) pto pump. It's not in the Northern catalog, but I emailed them to see if they can get it. If not, I'll have to call every place around and see what I can find. 17 is 1 gpm bigger than what I wanted, but could just go with a bigger cylinder so as to reduce the total amount of system pressure needed to do get the job done. Here are some calculations on piston size, flow, force, and speed (used 2250psi and 17 gpm and 30" long cylinder) that I got using those before mentioned calculators.

4" ram = 28,274lbs of force with extend time of 5.8 sec, cycle time 10.1

4.5" ram=35,785 lbs of force with extend time of 7.3 sec, cycle time 13.2

5" ram = 44,179 lbs of force with a push time of 9.1 sec. cycle time 16.6

If anyone has any input on ram size and extend times, and what they should be, let me know.

I am having a heck of a good time discusssing my plan of attack with all of you. Your input has been very valuable. This thread definitely went alot further than I anticpiated.
....

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TomG
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2002-02-18          35688

Duane, that's some pretty good work. I don't imagine there are that many people around tractor boards that could come up with those calculations--including myself.

In looking for a splitter valve, you're most likely dealing with open centred hydraulic systems on the tractor and likely a PTO pump as well. Open centred systems pump oil continuously while closed centred ones do not. Open centred systems only develop high pressure only when a control valve is operated. Otherwise, the pump circulated oil a low pressure through the lines and back to the reservoir.

Many valve assemblies sold can be used for open or closed centre systems, but a plug must be removed for open centre use. Valves also come in conventional and power-beyond types. A power beyond type would be required for many, but not all, hook ups to tractor hydraulics, but probably not for a PTO hookup. Anyway, some of these basic issues may affect the choice of a splitter valve.
....

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Murf
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2002-02-18          35693

OK, I'm going to screw up everyones logic again. Here (Thanks, Tom) is some more of that "Been there, done that." logic (T-shirts are available in the lobby & the beers on me, BTW). Cycle times on the cylinders are next to useless since you won't actually perform full-cycle motions. Once the block of wood has split open you will reverse the cylinders direction and not carry on through to full extension, so the cylinder will be stopped at about 10" from the end. Further, unless you are working alone, which is not recommended, you will not completely retract the cylinder either, there is no need to have a 24" opening if you're only splitting a 16" block. The most productive (INMHO) is to do the splitting with two people, one feeding in full blocks, the other operating and tossing the split pieces in a pile. So, following this train of thought, the cylinder will only need to travel from about the 5" open point, leaving a 19" opening for a ~16" block, to the ~8" open point (8" of penetration will normally split even fresh cut wood) equating to a 'real world' stroke of ~11" or less than half of the cylinders maximum travel. Therefore if you went with a 5" cylinder (22 tons force might do it, LOL) you would have complete cycle times of less than 8 seconds.... good luck keeping that pace up for long. In practice, if you had a cycle time of anything under about 30 seconds you could produce a staggering pile of wood in an hour or two. Best of luck. ....

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Duane
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2002-02-18          35699

All very good points murf. Indeed, there is a point where all the numbers and calculations in the world don't mean poo under real life circumstances. I have actually been wondering if I should reconsider getting a ram with 30" travel, and settling for a 24". I say to myself: "self, you might want that extra bit of distance to split those 24" logs." But then Myself responds "come one self, how many 24" logs are even in your wood pile right now?" And the aswer of course is 0. I cut everything about 18" to 20", so a 24" ram would certainly do the trick. Just do the math.

24" ram - 20" log = 4" of extra air to split. How's that for some mathematical calculations Tomg? lol ....

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Murf
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2002-02-18          35705

I think I can top that equation Duane. Try this one... 1 large pile of logs + 1 large chain saw + 1 front-end loader with fork set + 1 large shop + 1 woodsplitter + 6 employees wanting to get paid for a 'rain-day' = one mammoth pile of firewood... and best of all my back isn't sore afterwards, LOL. BTW, 'cause I know you're gonna' ask, the splitter is a 3pth model with a 24" x 4" ram driven by the factory remote on a Kubota L4200 (about 6 gpm @ 2000 psi). Best of luck. ....

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Duane
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2002-02-18          35707

You guys are gonna think I'm crazy, but I have been doing a little more thinking... scary huh? Anyways, I have been fretting about numbers lately, wondering if a 17 gpm pump would run the tractor too hard and bogg it down too much, then I started figuring some numbers using murf's last post. Murf, your 4" ram produces 25,133 lbs of force at 2000psi. I compare that number to what a 5" cylinder can produce at 1500psi, about 29,452 lbs. These numbers fill my heart with joy. Reason? I mentioned earlier in this thread that for every 1hp of drive, 1 gpm at 1500 psi can be achieved. This means that I can run a 5" ram at 1500 psi off of a 16 - 17 gpm pump without bogging the engine, and still have about 4000lbs more splitting force than your splitter. And if your splitter has enough power for you it most likely has enough for me. I guess what I am getting at is that I would probably never need to build much more than 1500 psi, but if I did, the engine bog would probably not be severe. SO... I finally got a setup I am confident will work...

17 gpm pump --- 5" ram --- 24" stroke

I'll update you all when I am finished... might be a little while. thanks again!! ....

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TomG
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2002-02-19          35719

Yes, it's good to move from theory to calculations, but eventually everybody has to just get the work done. And, here there's nothing better than real experience. In the meantime, theory and calculations are good for planning and even better for learning.

True enough, that the ram doesn't have to be moved further than it takes to split a log. Full ram cycle times would provide an excessively long time estimate for completing a job. On the other hand, 16" firewood (standard around here since most it goes in stoves) takes longer than 24" firewood. Knotty wood may require move ram movement and would slow the process. From tractor hydraulics, power steering run from a priority valve also would slow the process. But at some point, most everybody has to stop thinking and start doing. That point probably has arrived.

I do think that producing a huge pile of firewood in a working day from an 8 gmp (perhaps minus PS flow) maybe could be thought of as 'having enjoying optimal conditions.' However, once out of the world of theory, I've learned to accept that whatever works for someone is a good result. I don’t doubt that a lot of work can be done with 8 gpm @ 2000 lbs.

I don't think that there is cause to worry about the engine lugging. The system relief valve on the tractor hydraulics or a relief valve on the splitter valve or a PTO pump would prevent hydraulic demands from lugging the engine. Relief valves generally are adjustable, but as noted earlier, the setting to run a big pump from a small engine may be so low that a splitter may not have great force or would require excessively large cylinders.

....

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Peters
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2002-02-19          35726

When we started this tread, I stated that I had a PTO splitter in the barn that I had never used. I have only used one once in MA. I was only helping and I found it quite slow.
When I was cutting wood for the fire in KY I found I could cut in forest, split and stack approximately 1/2 cord or a short cord in one hour. To me a pile means nothing as wood look much more when not stacked. As I was cutting hickory and oak primarily and a long fire box (22-24") I moved from my 3.5 lb ax to a splitting mall.
I cut the wood, move the blocks near the trailer or truck, split the wood leaving the bark and debris in the woods and then load into the trailer. About 1/2 of the wood I do not even stand up as it takes less energy to split on its side.
I have found that many people do not know how to split wood. I learned from my father who still heats with wood and splits it at 76. The last time I visited uncle Alan at home in Ontario he was splitting wood at 95. I am not a large man, splitting wood is not brute strength, it is reading the wood, speed of the head of the ax and the turn of the wrist. The ax should never stick into the piece of wood. If the wood does not split then he side of the ax hit the wood.
Splitting is an art, just as many of the other old tasks were. To do it properly takes training. To do it efficiently take practice. As a child I used to wonder as my dad would tap the wood and it would break in two. I wish I was 1/2 as good as he today. ....

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TomG
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2002-02-20          35743

Yep, a couple of years ago I pointed out an ad for a used home made standalone splitter that sounded pretty good to a woman we know. 'Nope', she says, 'not interested, I've already got three splitters.' They were and are her husband, his brother and their son. Around here more people heat with wood than not. There aren't any mechanical splitters and few buy it already split--store bought I guess you'd say. Still, if we heated with wood, I'd probably just as soon have some mechanical help--too late for me to acquire new arts easily. Don’t know maybe I’ll have to take the subject more seriously. The reliability of new oil burners, maybe in combination with dirty rural AC is starting to make wood seem attractive. ....

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