Gear pump vs. 2 stage splitter pump?

[msjanket]

Is it preferable to have the adequately sized gear pump or the 2 stage pump on a splitter? Some people feel the gear pumps offer certain advantages. OR, does the engine have to be really huge to power through knotty wood? thanks

Mike

 

[kevin j]

Engine hp required to turn a pump is proportional to flow x pressure.

Two stage pumps are simply two gear sections in the same body. At low pressure both sections add together for say 11 or 16 gpm.
Around 500 to 800 psi, the large section unloads back to the inlet, then the engine can turn the small section to 2500 psi at 3 or 4 gpm

High flow x low pressure = max engine power used.
Low flow x high pressure = max engine power used.

Running a single stage pump means you get only the small stage, say 4 gpm, through the entire cycle. SLOW. Only use the full engine hp for brief time when it went to 2500 psi. Rest of the time, low hp and slow operation.

I would not run a single stage pump even if it was free. You waste time every cycle for the next 20 years.....

k

 

[kevin j]

forgot: powering through big knots requires force, which is pressure times cylinder size. nothing to do with engine size.

of course, bigger cylinder means slower speed, so the reason for bigger engine is to turn a larger pump and get the speed back.

k

 

[drmiller100]

buy the 2 stage.

run the engine at idle, and pretend you have a gear pump.

when you get bored, run the engine at WOT, and now you have 2 stage speed, and 2 stage power.

optionally. every time you cycle the 2 stage splitter, stop everything and count to 15 and pretend you have gear pump.

 

[wkpoor]

Not all gear pumps the same says grasshopper.
Simply put gears pumps are absolutely fantastic. Problem is you will need gobs of power to run them. My gear pump allows for a 7sec cycle time on a 26" stroke 4" cylinder. And no matter how tough the wood its always going to move at the same speed, no slowing down to 2nd stage to get through the tough ones. Drawback is the HP it takes to do that is enormous.

 

[mga]

The two stage pumps are gear pumps too, just two in one body. I've been running a 28gpm two stage Barnes pump for almost twenty years.

that's what i thought.

to answer the OP, two-stage pumps are like having two pumps assisting with the work load. these are ideal for splitters and why they're used most often.

also, it's common for them to be gear pumps...i don't think any other type would work for that condition.

 

[triptester]

Two-stage pumps were designed specifically for log splitters as they are the most cost efficient. When a single stage gear pump is used the engine required to power it can cost as much as a complete splitter with a 2-stage pump.

I have only seen one splitter manufacturer that uses a single stage gear pump with a small engine. PowerSplit/TimberDevil use what they call a Drive multiplier producer between the engine and single stage pump. With this setup they claim 28 tons force and 7 second cycle times with 9 hp. engine.

 

[Gologit]

Engine hp required to turn a pump is proportional to flow x pressure.

Two stage pumps are simply two gear sections in the same body. At low pressure both sections add together for say 11 or 16 gpm.
Around 500 to 800 psi, the large section unloads back to the inlet, then the engine can turn the small section to 2500 psi at 3 or 4 gpm

High flow x low pressure = max engine power used.
Low flow x high pressure = max engine power used.

Running a single stage pump means you get only the small stage, say 4 gpm, through the entire cycle. SLOW. Only use the full engine hp for brief time when it went to 2500 psi. Rest of the time, low hp and slow operation.

I would not run a single stage pump even if it was free. You waste time every cycle for the next 20 years.....

k

Well said.

 

[wkpoor]

Running a single stage pump means you get only the small stage, say 4 gpm, through the entire cycle. SLOW. Only use the full engine hp for brief time when it went to 2500 psi. Rest of the time, low hp and slow operation.

I would not run a single stage pump even if it was free. You waste time every cycle for the next 20 years.....

I think you got it backwards. Any single stage pump is whatever the volume is which could be very high. Actually a single stage splitter will be the fastest. My single stage has a 7sec cycle time with a 26" stroke. And it is always that speed since this is no 2nd stage to slow you down. The only reason for 2 stage is purely lack of HP.

 

[kevin j]

but that is the point: the single stage can only be as large as the engine hp will drive to whatever high pressure is selected. A 6 hp will only turn about 3 to 4 gpm at 2500 psi, so the single stage can only be the 4 gpm size.

There is not the option of picking a single stage at say 10 gpm without the engine hp to turn it.

It is not as though it 'slows down' to the small side, but that it 'speeds up' when it can drive both stages high flow at say only 600 psi.

yes, if you have the hp to turn the single stage at say 10 gpm it will go faster. But it will go faster yet with a larger two stage of say 7-10 gpm at high presure, and still using 20+ gpm at low pressure.

Sounds like that is not an issue for your machine as faster than 7 seconds is probably not desireable. I'd guess you have maybe 20+ hp engine on 20+ gpm??


Theoretical hp is (gpm x psi) / 1714

Factoring in some efficiencies, and the formula is also easier to remember, as
(gpm x psi) / 1500 = engine hp

kcj

 

[wkpoor]

Maybe I don't understand a 2 stage pump but I thought the 1stage was all it had and the 2nd stage was about a tenth of the first not a combined flow rate but a partial of. I at least understand a 2 stage pump is what allows small power to do big work at the price of speed.
I have tested the 2vs1 side beside and that 2nd stage just just kills productivity. Every time it shuttles down the cylinder is creeping along. Unless you have a whole pile of easy wood after a while of splitting that 2nd stage creep starts to add up to alot of wasted time. I personally would rather burn a little more fuel and giterdun than spend time watching a cylinder retract.
On the other hand the slowest splitter in the world is alot faster than an ax.

 

[wkpoor]

I fully understand the value of the 2 stage pump. But it is what allows a small engine to split big or tough wood at the price of speed which has been my point all along here. Yes they were a great advancement in hydraulics for splitters. I'm only trying to point out I have tested the exact same cylinder and beam setup with to different modes of power. Or to say it in another way if you had to identical splitters one single stage and one 2 stage being the only difference ( provided the single stage had some more power) the single stage would out produce the 2 stage.
A friend of mine said yrs ago they had a splitter powered by a c60 International Cub engine. He said that was a fantastic unit. Quite and powerful and sipped fuel. Single stage of course but the 4 cyl engine could do the job, thats why it worked.

 

[SWI Don]

wkpoor,

My splitter with a 28gpm two stage barnes and a 5" cylinder rarely shuttles down to low speed. It has to be a pretty knarly piece to get it to grind down and even then it will speed up once through the hard spot. My cycle times are ~ 5 sec ea way and most pieces are full speed all of the way. I did turn up the transition pressure up a bit. Not much as Cylinder Service said you will shear the input shaft if you go crazy. I run it with an 18 hp engine.

Now if i had a 40-50 hp engine I could single stage it and never kick down but my engine runs about $7-800 and the diesel at Surplus Center is just under $4000 plus radiator. Two stage 28 gpm pump is $479 and the 2.33 cu in single stage is about $315.

Now shopping around would give better deals probably on all things, I only gave $350 for my engine, but you get the general idea. A lot of guys on this board ar looking at TSC splitters, Huskey, Harbor Freight etc that aren't speed demons but they are inexpensive. As long as they don't get the opportunity to run a splitter with a fast cycle time they will not miss it. Unfortunatly they are on this board and have been exposed to several splitters with fast cycle times and some very clever designs.

Don

 

[wkpoor]

Thanks for posting Don. You must be the guy who has been for mentioned a builder of nice fast splitters.
From my own experience I can see the 5" cylinder making the deference over the 4" in amount of shuttle time. And the 28gpm would give good cycle times too. I have posted a couple of times in saying I prefer smaller cylinders and more pressure over big cylinders. 4 1/2-5" seems to be a happy medium. What size hoses do you use on the pressure and return?
I've mentioned that the diesel is thrifty compared to gas even as much as to say my tractor uses no more than the 5.5 Briggs. An 18Vangard (which I've had on mowers...darn good engine) would probably use more.
As for putting time on a big expensive engine.... I use my tractor quite abit throughout the year even splitting wood and I only put a little over 100hrs this past yr on the engine. At that rate it will still last me 40+ yrs.

 

[gary A.]

I agree with wkpoor

I have a homemade splitter that is about 12 years old and has split LOTS of wood. Lots of people borrow it and it by now has almost all the bugs worked out of it. It is a single stage pump with a 1954 wisconsin 13 horse motor on it and I will put it up against any splitter you can buy at the local farm store. It has been copied and made by 4 other people that I know of for sure. I don't know the exact pump gallonage but I seem to recall that it is about 16gpm. I have no pressure bypass and have heavy industrial hoses rated at 6000#. Way back when I built it and had a pressure gauge on it, it would easily reach 4500#. You can use all the formulas and theory you want but if I were to build another splitter I would for sure use a single stage pump. It slows down for nothing and the unloaded cycle time is the same as the loaded cycle time and for me it is about 5 seconds each direction. Only one time did I have a piece stuck on the wedge and I needed 2 come-a-longs and a sledge hammer to get the piece off. There is nothing wrong with a single stage pump. Another buddy downsized the same setup and uses a 7 or 8 gpm pump and drives it with an 8 horse briggs and it seems to work pretty well for him. I haven't used it but did help set it up.. It routinely reaches 4000# pressure for him. You cannot use farm equipment hoses rated at 2500# or else you would have hose burst problems and of course that would be way dangerous.. Get somebody that understands Hydraulic sytems to help you set it up and get the correct pump for your engine.. It is not rocket science. I know some people are going to disagree, but I would not have a 2 stage pump, even if I had to get a 4 cylinder car engine to run it because of the speed of a single stage... Just my opinion and my $ .03 worth..... gary

 

[triptester]

Gary A.,

I would like to know the make and model of one of those single stage pumps that you are running off of small engines . I have tried several different gear and vane single stage pumps up to 11 gpm add they have all stalled a 12 hp. engine before building any decent pressure. Also where do you find duoble acting cylinders rated over 3000#. I find single acting cylinders rated to 10,000# but double acting ones rated over 3000# are very rare.

 

[wkpoor]

I would like to know the make and model of one of those single stage pumps that you are running off of small engines . I have tried several different gear and vane single stage pumps up to 11 gpm add they have all stalled a 12 hp. engine before building any decent pressure. Also where do you find duoble acting cylinders rated over 3000#. I find single acting cylinders rated to 10,000# but double acting ones rated over 3000# are very rare.
triptester is online now Reply With Quote

I have run splitters like that before. Your engine becomes your relief valve as there is only so much power available for the pressure and volume it is trying to create. I personally wouldn't recommend running without a relief valve. That is the limitation and protection for your system.

 

[kevin j]

These discussions are comparing apples and oranges though!
The key issue that is varying is engine hp.

The size of the section of pump that goes to high pressure is defined by the engine hp. One stage or two stage it does NOT matter! The small section is defined by the engine hp.

A two stage pump simply adds another section in the same body. When less than maximum psi is needed, the larger gearset adds into the flow. You get way more flow to use the entire engine hp.
BTW, I published in an earlier thread topic here I think, but a two stage pump runs the small one always to the outlet. The larger section either adds to the flow from the small one (say 3 + 8 = 11 gpm out) or it unloads back to the inlet at almost no pressure. Then the outlet is just the small one (3 gpm for instance). The pump does not vary its displacement in any way, just loads and unloads the larger section.

Sure, a single stage pump is constant speed, but the two stage is not 'slowing down' from that speed. The single stage pump STAYS on SLOW speed always, as the max size that the engine can pull. The two stage runs at the same speed in low, or speeds up when pressures are low.

My 18 hp Briggs flat twin runs a 28 gpm to 800 psi, then shifts to low for 7 gpm up to 2500 psi.
Or I could put on a single stage pump and run 7 gpm all day, and use under 10 hp most of the time. SLOW! Or I could put on a 28 gpm single stage pump and a 45 hp engine to turn it….
Do the math and make your own decisions.

Of all the splitters I have used, my main complaint is speed, it is very rarely low force.
The only place I would ever consider using a single stage pump is if there was a free, big engine already there running say a processor or elevator, or farm tractor PTO pump package. Then you have more than enough power, so no reason to use a two stage.

But for building a machine, why would anyone put on a 30 or 40 hp engine to run 11 gpm or so, fixed at this maximum, when an 18 hp can do 28 gpm most of the day, just slowing down to 7 gpm at the tough spots?

 

[gary A.]

triptester, I do not know the make of the cylinder, but it came off of some industrial piece of equipment. I got it from the same place I got my pump. There is a local guy who buys and rebuilds a lot of industrial equipment such as forkifts, big cranes and other stuff I don't even know what it is. The pump came off of a 10,000 pound forklift. My wife has a digital camera but I don't know much about it or I would try to get some pictures of the setup. wkpoor, you are correct that the engine is the relief valve. I didn't say it wouldn't stall the engine. But when I had a gauge on it, it would't stall until pressure was at or above 4500 pounds. The smaller pump that my buddy used got it at a local hydraulic place in Omaha. I don't remember the size exactly but seem to think it was around 6 or 7 gpm. He has a relief valve built into his directional valve and has it cranked up to around 3800-4000. I'm not saying it is the best setup or the best system, I'm just a cheap old bastard who would not buy one for over $1000 dollars back 1994 when I built this one. I already had the engine and an 8 inch beam so I stopped at the place that rebuilds industrial equipment and got the pump and cylinder for $ 200. I had wanted a smaller buzz saw for a while and put the splitter on one end and the buzz saw on the other. Total be said I probably have about $500 in it but uncounted hours of time and setup to build. It has split a ton of wood through the years and still works pretty darn good.... If you want I'll see if I can figure out the digital camera and how to load pictures on here but I am not making any promises as most of this computer stuff kicks my a&&... gary

 

[triptester]

Gary A.,

Pics or any pump info would be great . I would like to have the option to use other pumps if I could get high enough gpm and pressures with a small engine.