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log splitter hydro question

Post in 'The Gear' started by evamaxx, Jun 26, 2013.

  1. evamaxx

    evamaxx New Member

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    i see most splitters use 2 stage pumps with small engines 5-say 12 hp but there some draw backs at what hp eng can u use a single stage pump and how do u size a single stage to the motor? any help in this area from the hydro pros thanks mark

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  2. Woody Stover

    Woody Stover Minister of Fire

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    You might want to consult the motor heads over in the Gear Forum....
  3. blwncrewchief

    blwncrewchief Burning Hunk

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    It works like this. Most all log splitters use a 2 stage pump to get the best of both worlds and that is speed and splitting force versus the hp. When matching a hyd pump to an engine you have to match the flow and the pressure. Think of it as having a transmission in your car. If you only had first gear (smaller pump) you could climb a steep hill but if you have to drive a mile to get there it would take forever since you could only go 20 mph. If you only had fourth gear (large pump) you could go 80 mph and get there fast but when you hit the hill it would stall because your car didn't have enough power to climb the hill in fourth gear. The calculation for the amount of power required for a hydraulic pump is: HP=(PSI x GPM) / 1714. So as you can see by the calculation any time you increase the pressure OR the flow it will require more power.

    So let's look at a couple numbers for example. Say we have a 6hp max engine. Since as far as the pump selection is concerned hp is always the deciding limit. Lets find the maximum flow at high pressure we can get out of the 6hp at 3000psi since that is generally the maximum pressure on most splitter hydraulic components. If we go 3gpm and 3000psi it would take 5.25hp so that would be ok. Any higher numbers would stall the engine. Now if we use the common 4" bore cylinder we can calculate out the two end numbers we need. With a 4" cylinder, 3gpm, and 3000psi we would get about 38,000 pounds of force or 19 tons, and we would get an average travel speed of 55" per minute. The 19 tons is ok but the 55" per minute would give a cycle time of 50 seconds for a 24" stroke! That would suck. If we try to speed it up we calculate that 11gmp at 800psi would take about the same 5.2hp. At 11gpm we would get a travel speed of about 200" per minute so our cycle time would now be about 13 seconds. That's much better, but wait. Now we only have 800psi so now our maximum force would only be about 10,000 pounds or 5 tons. If we want the 11gpm and 3000psi it would take 20+hp. The obvious problems with just using the 20hp engine is a 6hp engine cost about $200 and a 20hp engine cost $1000. The 20hp engine is also going to use allot more fuel. And the only gain for all that expense is the increased speed for the short amount of time we would be actually using over 5 tons of force.

    So there is where a 2 stage pump comes into play. If the first stage was 11gpm and switched over at 800psi to the second stage at 3gpm we could get the fast speed until 5 tons and then it would switch to the second stage and we could get up to 19 tons at the slower speed. A 2 stage pump is as close as you can get to getting the best of both worlds and they are cheap enough it is pretty much senseless not to use one on a splitter.
    n6crv likes this.
  4. evamaxx

    evamaxx New Member

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  5. evamaxx

    evamaxx New Member

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    thanks for the replyi think i understand it ive built a couple splitters in past years and now i think the pump went bad in the splitter i use alot i split well over 150 cords of all oak per year this pump is aprox 4 yrs old i think conseve 500 cord of oak i seen outher ones that have single stage pump when it kicks in to lowgear it really slow the stoch preset was 2250psi i ajust to 2900 psi its a barnes 28 gpm with a 2cyl 27hp kohler pushing a 6x"30" cyl with a air to air fan force cooler since it only has about 16 gal sump new pump around 300$ wanted to hear outher opions all healp would be good i was thinking about single stage 11 or 13 gpm pump thanks mark
  6. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    Taking it to the Gear room where lots of folks can help with this stuff.
  7. MasterMech

    MasterMech Guest

    Single stage pumps do not have a "low gear". With that kind of engine power on tap, you're better off with the big 28 gpm pump.

    We want pictures of this beast!
  8. blades

    blades Minister of Fire

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    From the sounds of it your 2 stage 28 ain't kicking down. Although the way you present information makes you sound like a troll. Your tank is too small, common fault. I will bet your fittings are restricting flow causing a heat build up. Valves wear out faster than pumps. An internal leak between spools and bypass of valve will act like pump is bad. Same for an Internal leak on cylinder seals. I do not see any reason to set the bypass so high, doesn't decrease cycle time, does reduce safety margin.
    What size are your cylinder and valve ports? What size are your high pressure lines?
  9. evamaxx

    evamaxx New Member

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  10. evamaxx

    evamaxx New Member

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    hi psi line to pump is 3/4 id all fittings are 3/4 the by pass or hi psi side is high so it cuts through knots ill tri to post picts idid of the wood pile thanks problem is motor runs pump spins i guess no psi wedge dont move i think the only restriction is pump out is 28gpm and the 3/4 valve is only 25gpm i cant find a detent valve rated more than that any ideas thanks mark im not a troll
  11. evamaxx

    evamaxx New Member

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    heres some pic of splitter in horz pos.

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  12. evamaxx

    evamaxx New Member

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    sorry i guess im behind learning curve posting picts
  13. blades

    blades Minister of Fire

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    get a gauge and set it up so that it can be inserted in the lines, pump to valve, valve to cylinder ram out. this will allow you to see where pressure is or isn't.
    Ram not moving- pump or might not be the pump it self but the drive coupling. feed line to pump collapsing or if there is a screen in tank output it could be blocked
    Valve stuck in bypass mode, they do break down you can take the bypass section apart steel ball and a spring in there spring could be broke. you can also take the spool section apart things wear and get gummed up in there.
    Cylinder - if the internal seals on it are shot you can check by deadheading the ram, and removing the cylinder return line from the valve place in clean bucket let drain out. then run eng. with valve in extend position if fluid exits in to bucket seals shot ( safer to do with gauge) make sure that hose can't go whipping around by it self though.
    These are the basic system checks. Hope it helps.

    Shearing through wood on a v/h unit is not the best idea, in good hardwood you run a severe risk of bending the foot plate and/or springing or bending the beam. ( have T shirt) ( had one customer come in with his unit, the foot plate was 80% ripped off the beam)
    triptester likes this.
  14. bioman

    bioman Burning Hunk

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    I see in your first picture, looks like the pump is not tight to the mounting bracket. Might be something going on with the coupling.
  15. evamaxx

    evamaxx New Member

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    it does look like its loose but its a shoulder in casting the pump spins ok i need to test the psi ill get a guage and manifould monday the last 6 mo ive working on a new splitter 36hp diesel and singlestage11gpm pump im mounting in bob attach plate on my 743 i will splitt upside down with out picking up wood untill its split using the aux circuit from the seat in cab heres some picts if i can post them

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    bioman likes this.
  16. blades

    blades Minister of Fire

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    That is something I need to make as well ( bobcat splitter) too many other projects ahead of that one though. Hope you gouged out the beam top and beveled the weld area on that wedge for your first weld pass.( oh and Maxed out the welder as well if you didn't preheat)
  17. evamaxx

    evamaxx New Member

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    thanks for the welding tips i bevel the wedge and welded it with a lincoln 300 amp mid wirth 80k .045 wire 2 pass the back brace not there yet i hope it dont bend mark
  18. Jags

    Jags Moderate Moderator Staff Member

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    Nice work on the new splitter. With that tall of a wedge it will be putting a pile of force on the welds. Make double darn sure that you have that thing really, really attached well. It appears to be a 5" ram, but is kinda tough to really tell from the pic. A 5" ram on an 11gpm pump is not going to break speed records.
    smokinj likes this.
  19. smokinj

    smokinj Minister of Fire

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    Somebody needs to watch the paint dry. Here let me pull the handle better be an auto return mode to.;)
  20. evamaxx

    evamaxx New Member

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    thanks jegs i got the wear plate on top of beam tonight i plan on bolting on 1/4 x3 alum bronze on bottom of push plate to take ocare of the wear factor im not sure of the speed sombody said something to the affect it will be slow ive not done the math on this one hopefully i wont have to go to a 4" cly if any body knows what speed it would be that would help my bobcat book says its a 11 gpm pump but not sure of the rpm i dont run real fast little more than 1/2 throtle most times thanks mark
  21. basod

    basod Minister of Fire

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    Most of your aux ports are probably not going to get 11gpm
    ID of a 5" cyclinder is probably ~4.5"
    3.14(Pi)xR^2 x Length x .004329(in^3/gal)
    for a 24" cylinder you're looking at ~ 1.7gallons on the out stroke, and less on the return due to the shaft volume
    if you have 11gpm pump that's 0.183gal/sec you're looking at a 9-10sec outstroke and ~6-7return - and this is totally dependent on your engine/rated pump speed
  22. evamaxx

    evamaxx New Member

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    thanks that sounds kinda slow i will have to test to find out thanks mark
  23. Jags

    Jags Moderate Moderator Staff Member

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    I run a 16 gpm on my 5" cylinder and would not want to go any slower. If I ever wear it out, it will be swapping to a bigger motor and a 28 GPM pump.

    Trust me when I say - 11 gpm on a 5" cylinder is gonna be slow.
    smokinj likes this.
  24. evamaxx

    evamaxx New Member

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  25. Jags

    Jags Moderate Moderator Staff Member

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    If I get your question - a 28GPM two stage pump will require 14+ hp.

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