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Question on PTO splitter build

Post in 'The Gear' started by mudr, Sep 4, 2013.

  1. mudr

    mudr Member

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    Hi guys. I am tossing around the idea of building a spitter. Some background: I don't really need a splitter, and can't justify going out to buy a new one now. However, I have an old John Deere B two cylinder tractor that hasn't seen much use in, well, a long time. I'd like to give the old girl a job to do and wouldn't mind spending some time in the shop with the old man (he gets cut to 40 hrs/wk in the winter and hates it) building a splitter. So, I'll admit the main reasons for building the splitter are to have a new toy to work the tractor and to play in the shop. Here is what I am dealing with:

    -1393 Deere model B. PTO is rated at 25 hp, it does not have hydraulics or three point hitch: http://www.tractordata.com/farm-tractors/006/9/8/6988-john-deere-b.html

    -I'd like to get a pump such as the following (ebay link just below). The standard sizes seem to be 11, 16, and 21 GPM. I am thinking of the 21 gpm because difference between it and a 16 is rather small (within $40), and with a larger pump I can run the engine at a lower RPM to get the flow. While these old Deere two-bangers are rather easy on fuel, it'd be nice to run at a lower RPM. What do you think on the 16 gpm vs 21 gpm? Also, there is Prince Pumps (such as the one linked below), they seem to be the priciest pumps. There is also a "Chief" brand which seems to be a tad cheaper. Though, I admit the one on ebay below is a really good price for a new Prince.
    http://www.ebay.com/itm/New-Prince-...Pump-HC-PTO-1A-21GPM-540rpm-NEW-/360702095463

    -I hope to find an old splitter on craigslist, typical tow-behind model. I've seen some older ones that have the cylinder, I beam, and axle/frame, but no motor/pump in the $150 range. This would be the ideal setup, if not, I would build from scraps I can scrounge up.

    -If I build, I'd go for a 4 (5?) inch cylinder with a 2 inch bore. Thoughts? I'd probably go in the 24 inch range, as a 20 would cut it close on some of my splits.

    -A buddy of mine welded up his own reservoir tank and would be willing to weld one for me. I've seen the rule of thumb being "match the gallons of your reservoir to the gpm of your pump", thoughts on this?

    There is a lot here, hopefully some of you can chime in. I think I can do this in the $800 range. Yes, that's getting close to buying a new one, but the added bonus being that I can use that $400 pump for other things on that tractor as well, increasing it's utility. Andddd, I can play with my tractor. So, it's also about fun!
    Last edited: Sep 4, 2013
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  2. ewdudley

    ewdudley Minister of Fire

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    1939 JD B puts out about 20 belt horsepower, on a good testing day, PTO would be a little less. Fuel efficiency for the gas models was good, but not out of the ordinary. Same vintage Farmall C is 6% better, for instance. JD 720 diesel on the other hand was very efficient back in the day.

    21 gpm at 2000 psi is 24.5 horsepower, so your B doesn't have the oomph you need to get full wallop out of the pump. Nonetheless I'd still say get the bigger pump for faster ram speed and let the tractor lug down to achieve maximum pressure. With that big old flywheel and 175 cubic inches, it'll lug.

    For cylinder size need to compute how much force 1500-2000 psi will generate according to surface area of the piston and choose the smallest piston that will generate the required force.

    Don't know about tank size. I would think if you can keep the fluid cooled then no bigger than necessary for the hydraulic cycle.
  3. mudr

    mudr Member

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    Thank you for your response.

    Has anyone here run a pto pump like this, especially on a splitter? What do you think of it's usefulness?
  4. ewdudley

    ewdudley Minister of Fire

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    We ran 540 RPM pumps for Farmhand F11 loaders and bale accumulators, I think they were Prince pumps, about 20 GPM. Ran them for many hours over many years and I have no recollection of them being short-lived or prone to failure. I would think they would be more reliable than a 3600 RPM pump.

    If 15 GPM (less than full speed throttle) will move the cylinder fast enough and 1500-2000 psi will supply the required force, than it should work well. Be sure to use 1" or larger hose on the return side.

    On the loaders the reservoir tank was only about five gallons. The main cylinders were long and fairly small diameter so I would imagine they would radiate heat well, hence no need for the recommended "1 X GPM" tank size you keep hearing.
  5. MasterMech

    MasterMech Guest

    Running the B is going to be fun but it's going to drink a lot of fuel compared to a self-powered splitter. PTO powered splitters tend to be pretty slow compared to stand-alones. The pump will not put out it's full GPM unless you wind the tractor engine up to full PTO RPM.
  6. mudr

    mudr Member

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    Thank you, and I understand and accept the added fuel cost. Here's the thing: I expect to use 16ish face cord (ok, ok, 5.1 "Real Cords") per year. If I can split a face cord per hour (wild ass guess), and use ~1.5 gallons/hr (rated at 2.0 at full RPM), I'm going to use 24 gallons per year. Yes, much more than a self powered one, but that's not bad considering the wood stove is preventing me from running 3-4 tanks of fuel oil. It will be the only real work the tractor gets, and I don't want to just leave her sit in the shop. Finally, I'd get to have the pump for other uses with the tractor.

    By some the calcs I've done, I can run a 5X24 cylinder with a 2 inch rod with a cycle time of 14 seconds. That was calculated assuming I run the 21 gpm pump at a lower throttle to save gas, so I used 16 gpm in the calc (3/4 throttle) (http://internationalhydraulicsus.com/logsplitter-speed-calculator/). I'd rather run the 21 at a moderate RPM and "only" produce 16 rpm to save a bit on fuel. At that 3/4 engine throttle, let's say I have 1500 psi, that will yield 15 tons of force. That will split the majority of my stuff, and I can run full throttle and still get 21ish tons. http://www.knighthawksupply.com/calccylforce1.htm
  7. ewdudley

    ewdudley Minister of Fire

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    According to the Nebraska testing a low compression B will use a little less that 2 gal per hour at 20 hp, 1 gal per hour at 4.38 hp, @ 1150 RPM engine speed. Presumably you'd be averaging less than 4.38 hp and running at less than 1150 RPM, so I'd say 1 gal per hour would be a worst case.

    You should get about as much PSI at the lower RPM, just lower gpm.
  8. MasterMech

    MasterMech Guest

    One thing's for sure, if you build it, I want video of a B splitting wood. ;)
  9. Jags

    Jags Moderate Moderator Staff Member

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    To clarify - engine rpm has nothing to do with PSI. Volume (GPM)? Yes. PSI? No. Pressure is regulated by the pressure relief (often built into the control valve of a splitter). PSI (or tonnage of the splitter) is calculated using the pressure relief setting and the square inch displacement of the end of your cylinder rod.
  10. mudr

    mudr Member

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    So, in laymans terms: revving the engine will speed up the cycle time by flowing more fluid (increase GPM), but do nothing to tonnage, which is dependent upon PSI which does not change based on RPM. Correct?
  11. Jags

    Jags Moderate Moderator Staff Member

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    Exactamundo.
  12. mudr

    mudr Member

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    Excellente.
  13. ewdudley

    ewdudley Minister of Fire

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    IF the torque of the tractor PTO is sufficient to raise pump output PSI to the relief valve pressure. We seem to be lacking this specification. A 20 hp power source will develop about 195 ft-lb of torque on a 540 RPM shaft, and somewhat more as the engine lugs down below peak horsepower. Will the pump in question provide the desired PSI with 195 ft-lb of torque?

    [edit:]

    Found some numbers from Prince pump data sheets:

    2000 output psi requires input torque of 312.2 ft-lb @ 540 rpm. In like proportion 1000 psi output requires 156.5 ft-lb input torque @ 540 rpm.

    JD low compression "B" is about 18 PTO hp, or 175 ft-lb torque at 540 rpm. Estimate max torque as 125% of max horsepower torque at 60% max horsepower engine speed gives 218.75 ft-lb torque @ 324 pto rpm.

    If 156 ft-lb gets us 1000 psi and 312 ft-lb gets us 2000 psi, then 219 ft-lb works out to about 1400 psi.

    Estimated gpm equals 324 divided by 540 times 21; 12.6 gpm at max steady state pressure. If you're normally running 3/4 engine speed then gpm would be about 16 gpm most all of the time.

    So max pressure would be 1400 steady state, but you could wind it out and charge into it, and the flywheel would give you a nice 2000 psi spike when needed.

    Prince says you can run the pump at 110% of rated speed and working pressure can run 2250 psi if you wanna, so obviously you need to punch out the block a little, install a pair of Cat diesel pistons to take the compression ratio from stock 4.1 up to something closer to 10.0, port, polish, balance.... and before you know it you'll have the 40 hp you need!
    Last edited: Sep 6, 2013
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  14. Stihlmike

    Stihlmike Member

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    I design big rigs for a living. Set up 80000# winch trucks. We reduce oil tank size by installing oil coolers. I can talk to our hydraulics guru if you'd like. Might be able to get you some deals on the parts.
  15. mudr

    mudr Member

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    ewdudley: Wow, you took the ball and ran with it there on those calcs. I my take away: at 3/4 throttle I'd have 1400 psi with 16 gpm, but can obviously lean in to it with the throttle (or soup up the ole engine). With those stats, I'm definitely going to need a 5 inch cylinder rather than the 4. I'd have the gpm, but need to maximize the use of the lower psi.

    Stihlmike: Thank you for the offer, if I need some deep, guru level hydraulics questions answered I will send them your way.
  16. ewdudley

    ewdudley Minister of Fire

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    Just to clarify, estimated performance:

    Assuming 18 PTO horsepower, and that (WAG) max torque is 125% of max hp torque at 60% of max horsepower rpm:

    At 60% engine speed, flow would be 12.60 gpm @ 1400 psi, all day long.

    At 75% engine speed, flow would be 15.75 gpm @ 1300 psi, all day long.

    At 100% engine speed flow would be 21.00 gpm @ 1122 psi, all day long.

    I think 1400 psi would be the maximum sustainable psi without stalling.

    When you hit a tough spot you can release the valve (hopefully) before it stalls, apply full throttle, then re-open the valve and the flywheel will take pressure up to the relief valve maximum of 2000 psi momentarily before the valve is released again and the process is repeated. With a relief valve in place and the stout PTO drive train this mode of operation should not put any undue strain on anything at all.

    (The pump 'maxes-out' at 39.7 input horsepower, 594 rpm, 23.1 gpm, 2250 psi. http://www.princehyd.com/Portals/0/pumps/pumpsPto.pdf )

    I don't know what your capacity is for self-restraint, but should you yield to the temptation of performing field modifications to the governor spring I can say from my experience that low compression A's and B's can run at 115% of rated RPM for years on end without much to worry about.
    Last edited: Sep 7, 2013
  17. mudr

    mudr Member

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    THANK YOU for everything. One question regarding the above: Why the inverse relationship between GPM and PSI? If you crank the engine up, my brain says that you should see an increase in both the PSI and GPM, as the PTO is cranking faster turning the pump harder...
  18. ewdudley

    ewdudley Minister of Fire

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    As Jags points out, psi doesn't necessarily relate to RPM. If your power source can maintain sufficient torque over the full range of the pump's range of RPM then it can maintain constant pressure.

    From the pump data sheet we can calculate that it takes 312.2 ft-lb torque at 540 RPM to get 2000 psi. If you ran at 270 RPM with the same input torque of 312.2 ft-lb of torque you'd still have 2000 psi, just at half the power.

    But the B doesn't have enough wallop to generate 312.2 ft-lb of PTO torque at any RPM. However since tractor engines are designed to lug -- meaning they generate more torque at WOT as RPM decreases, to a point -- then as the engine lugs down to lower RPMs then pressure can increase even though power is falling way off.
    Last edited: Sep 7, 2013
  19. mudr

    mudr Member

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    Thank you again. One last question. Given this potential build (and your obvious knowledge regarding the numbers) should I stick with a 5 inch cylinder or can I get away with a 4 incher?
  20. ewdudley

    ewdudley Minister of Fire

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    Only ever built one splitter, it was 5 inch just because that was what was available at the time and it looked like it would do the job. We ran it off (at the time) big tractor hydraulics, 13 gpm @ 2250 psi. I would say the cylinder was bigger than it needed to be. Although it would go through absolutely anything it was slow and provided welding lessons at inconvenient times.

    If you look close at these so-called "22 ton splitting force" machines, they run two-stage pumps that claim to put out 3.62 gpm at 2000 psi into a four inch cylinder with "MAX psi" of 2500. Back when I got my arithmetic merit badge pi times two inches squared times 2500 psi was 31415.927 pounds of force, but apparently these days we can multiply actual force times 1.4 to get "splitting force". The PTO pump you're looking at says it can go up to 2250 psi, which you can achieve by using tractor flywheel cycling for problem chunks, so I'd say if a dinky pump can do the job with a four inch cylinder then you should have no problem with the pump and tractor you're looking at.

    Hopefully somebody will chime in with better and more relevant experience, but I would say go for a smaller faster cylinder that will walk rapidly through 95+% of your rounds and plan on doing some noodling on the problem chunks -- if it even comes to that.
    Last edited: Sep 7, 2013
  21. mudr

    mudr Member

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    Huge thanks my friend. If you ever head west about two hours, stop by and I owe you a few cold ones.

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