Sizing pump to engine for highflow wood splitter

[MattBanchero]

I'm in the last stages of building my monster splitter. It has two massive cylinders. I am considering a 26hp kubota 3 cylinder diesel to power it, but I'm unclear if I can set the engine to turn at it's rated 3600rpm for the small stuff and let it bog to 2000rpm on the tough wood.

This is the second prototype, I'm estimating that the splitter should be peaking at about 1000psi for most splitting applications and I'd like to be running 35gpm.

With 1 gpm at 1500psi per hp... 1000psi x 35 gpm=35000, 35,000/1500=23.3 hp required

So with a 26hp engine I should be good for most stuff.

Here's the question. The engine is rated for 3600rpm, so that's how I'll size the pump to get 35 gpm. But the peak torque for the engine is at 2000 rpm. If I bog the engine down to 2000rpm on something really tough, that will lower the flow to (2000/3600) X 35gpm=19.5gpm

(26hp x 1500)/19.5gpm=2000psi

So with a single stage gear pump I could be good for running 2000psi?

Is that right, can these small diesel engines tolerate those kinds of fluctuations in rpm, or am I setting myself up to destroy this engine?

 

[ChoppyChoppy]

35hp Kubota, 3000rpm, it goes down to about 2600 at 3000psi. 30gpm pump.

 

[blades]

Why run a single stage Pump? With a 2 stage I would think you could run Eng in its best efficiency/power range- namely about 22-2600 rpm for a small diesel, still have the high flow rate for 95% and it would switch over to Low flow High pressure for the other 5% with out bogging the eng. The switch over pressure on the pump can be adjusted or speced from supplier.

 

[MattBanchero]

Why run a single stage Pump? With a 2 stage I would think you could run Eng in its best efficiency/power range- namely about 22-2600 rpm for a small diesel, still have the high flow rate for 95% and it would switch over to Low flow High pressure for the other 5% with out bogging the eng. The switch over pressure on the pump can be adjusted or speced from supplier.

I cant find a 2 stage pump with the right flow or pressure settings for what I need. The biggest I've found are 28 gpm with a 650psi setting for the stage change. Do you know of someone who builds these custom?

If I could find one, I'd run a 25hp gas engine and keep it cheap.

 

[MattBanchero]

35hp Kubota, 3000rpm, it goes down to about 2600 at 3000psi. 30gpm pump.

.85

2600rpm/3000rpm=.86,
3000psi x 30 gpm/1500=60 hp

.86x60hp=51.6 hp

I'm not doubting that the dials show all this on your machine, but if the numbers are correct, you're describing getting 51.6hp out of a 35 hp engine?

 

[muddstopper]

What size cyl's and rod size and what lenght stroke. What kind of force (tons)do you think you will need that you think you can get away with just 1000psi.

While using two cyl will give you more tonnage at a given pressure than a single similar cyl will, it will also cut the speed in half. 35gpm of oil sounds like a lot of flow, but if you split it between two cyl, you end up with about 17.5gpm per cyl. While a single stage gear pump will give you the flow and pressure rates you are looking for, the minute the pressure reaches above your 1000psi you think you will need, its going to stall the engine. The engine will start bogging and slowing down and eventually stall, maybe before the split is made. I feel that letting the engine bog, and maybe stall, to reduce flow is going to be pretty hard on the engine. If using a 2 stage pump, biggest I have found has been a 28gpm, you can set the unloader on the pump up to 1000psi so that you have the full 28gpm flow at 1000psi and at that point the unloader inside the pump will switch to low flow high pressure and allow you to build what ever pressure is needed to make the split. Of course that 28gpm high flow is still split to 14gpm per cyl so you will see a real reduction in cyl speed as soon as the pump does kick down to high pressure low flow. This reduction would only be momentary because as soon as pressure requirements go below the 1000psi unloader setting the pump would revert back to low pressure high flow.

There is another option, but without knowing cyl size and tonnage you are seeking it would be hard to give any recommendation. Just also remember that large cyl's dump a lot of oil back to tank on the return stroke and is your control valve rated for those extra flows. In a nut shell, you could use a high/low double pump setup. With this type of setup you would also need some extra plumbing and a unloader valve to dump oil back to tank. With a double pump set up, it will work very similar to a two stage pump, but you do get the benefit of maximizing pump to engine hp combinations to get the required flow for speed and maximum pressure for force. You can pull the 35gpm at 1000psi or 17.5gpm at 2000psi with your little engine and you can increase speed by using the second pump section to provide more flow at a lower pressure by letting it dump extra fluid back to tank thru the unloader valve at a preset pressure, (1000psi) so that under your high pressure, you are still getting the force you are seeking. This would give you more low pressure speed and more high pressure speed than using the 28gpm 2stage pump. Of course its going to cost you a little more to set up as well, but I think it would be a better option than stalling and bogging your engine on every split. If you endup having to replace the engine often, the hi/low double pump setup would probably save you money in the long run.

 

[blades]

Just for grins, what size ports on the cylinders? If you are trying to maximize speed then you need ports large enough to handle that flow-1/2" ain't going to do it.
Speed is dependent on how fast you can fill & empty the two sides of the cylinders. 35 gpm pump can only punch so much through a hose , hard line & ports and valves. They need to be rated for the pump flow as well.

 

[muddstopper]

Just for grins, what size ports on the cylinders? If you are trying to maximize speed then you need ports large enough to handle that flow-1/2" ain't going to do it.
Speed is dependent on how fast you can fill & empty the two sides of the cylinders. 35 gpm pump can only punch so much through a hose , hard line & ports and valves. They need to be rated for the pump flow as well.

Since he is trying to fill two cyl at the same time he would only be putting half his flows to each cyl. So 35gpm split between two 1/2in ports. Where the problem will most likely start when he is combining those two flows back into one flow for return back thru his control valve before going back to tank. Not knowing the size of his cyl bore and rod, the actual flow back to tank would be impossible to estimate. The problem of to much return oil can be solved using a dump valve on return stroke, it just adds cost to the build.

 

[ChoppyChoppy]

.85

2600rpm/3000rpm=.86,
3000psi x 30 gpm/1500=60 hp

.86x60hp=51.6 hp

I'm not doubting that the dials show all this on your machine, but if the numbers are correct, you're describing getting 51.6hp out of a 35 hp engine?

Your math isn't correct, I can only guess.
I don't know how to spec it out, but I do know how to call people that do.

Pumps were spec'd out by Permco for that engine size. (1 pump for splitter)

 

[muddstopper]

Valley isnt your pump a multi sectional gear pump?. I am not going to speculate on how its setup as it would only be guesses. There is a lot more going on with your processor than just a regular splitter, and a lot of ways to do what your processor does. I have actually ran BlockBuster machines, but at that time I was looking at buying rather than building so I didnt pay any attention to how the hyd worked.

 

[ChoppyChoppy]

30gpm pump for the splitter, and 2 around 10gpm for everything else.

The "by the book" Calcs don't work for splitters, you can get away with more pump on less engine.

 

[Del_]

I cant find a 2 stage pump with the right flow or pressure settings for what I need. The biggest I've found are 28 gpm with a 650psi setting for the stage change. Do you know of someone who builds these custom?

If I could find one, I'd run a 25hp gas engine and keep it cheap.

You ought to go 2 stage pump. It will pay for itself quickly staring right off with a 28 gpm two stage only needing about 16hp. I've got a 28gpm two stage driven by an 18hp Briggs IC that has been in use now for 26 years. Same motor, same pump. 35 gallon hyd tank.

 

[muddstopper]

30gpm pump for the splitter, and 2 around 10gpm for everything else.

The "by the book" Calcs don't work for splitters, you can get away with more pump on less engine.

Well, I half way agree with you, but only up to a point. One thing left out of the OP calculations is actual pump efficiencies. Consider gear pumps lose flow as the rpm are reduced and then remove about a additional 15% flow because of the efficiencies losses internally with the gear pumps, actual flows might not be anywhere near the advertised rate. Few people own or have access to a flow meter to check actual pump flows, so all you have to go on are the advertised rates. Not saying your flow rates are not as advertised, but they may only be theoretical numbers and not actual numbers. Without hooking up a flow meter, you would have no way of knowing. I am reasonally sure that manufacturers do pump test their products for design purposes.

 

[MattBanchero]

Well, I half way agree with you, but only up to a point. One thing left out of the OP calculations is actual pump efficiencies. Consider gear pumps lose flow as the rpm are reduced and then remove about a additional 15% flow because of the efficiencies losses internally with the gear pumps, actual flows might not be anywhere near the advertised rate. Few people own or have access to a flow meter to check actual pump flows, so all you have to go on are the advertised rates. Not saying your flow rates are not as advertised, but they may only be theoretical numbers and not actual numbers. Without hooking up a flow meter, you would have no way of knowing. I am reasonally sure that manufacturers do pump test their products for design purposes.

The main test for hydraulic flow is how fast does the cylinder extend and retract. Then you can run the numbers back to get your flow rating.

 

[muddstopper]

The main test for hydraulic flow is how fast does the cylinder extend and retract. Then you can run the numbers back to get your flow rating.

Yes and no. for one thing, one stroke in and out isnt going to be very accurate determining flow rates. 100 repetitive strokes will get you in the ball park. No load strokes also wont take into account internal leakage of the pump when pressure builds. A pump might have %5 internal leakage at 100-200psi no load flow and that leakage jump to 15%-20% leakage at 3000psi. Best you can come up just using stroke speed is going to be an "about" number of gpm. For a wood splitter those "about" numbers are plenty close enough. We are not splitting hairs, we be splitting wood. A hydraulic engineer will use all those theoretical numbers, flow curves and such to design a system and then build a prototype to test those theories and then adjust the numbers to what works in the field. Just because a book says something will work, if you find what works in the field doesnt match what the books say should work, then you go with what works in the field.

I have more than just a passing interest in your twin cyl design because I am building a processor using twin splitting cyl. Post a little more information about size of cyl's and expected splitting speed and force you are looking for. Putting real numbers in the equations makes understanding the direction you are going a lot easier to understand.

 

[MattBanchero]

Two, 4.5" bore cylinders, 3.5" rod, 18" stroke. It's similar in function to a Rex 800 with reciprocating stroke.

 

[ChoppyChoppy]

On a gear pump, 15-20% loss from what I e seen.

Cycle time with the factory pump which was 24gpm? (I forget and I'm too lazy to scrape ice off the car to go the shop) was 7 seconds. That's extend and retract. Now with the 30gpm pump it's 5 seconds.
I think it's a 4" cylinder with 3" rod, again though, off memory.

Even 5 seconds is rather slow, but without putting a larger engine, hoses, valves, etc it's the quickest it will be.

The book numbers figure horsepower to run something at the set psi. A splitter won't run at that psi constantly. Splitting wood I might see 1000 psi average, which on a 30gpm pump requires about 15hp. I've only had the splitter not split something maybe a dozen times out of around 1200 cords.
Figure too it's 18 ton, pushing through a 6 way wedge.

 

[muddstopper]

Two, 4.5" bore cylinders, 3.5" rod, 18" stroke. It's similar in function to a Rex 800 with reciprocating stroke.

What size are the ports on your cyl, you will be dumping a lot of oil back thru the control valve on the return stroke. What flow is your control valve rated for. I havent done the math but guessing around 60gpm for return flow, might be more considering the size of the rod. Might want to do the math and think about incorporating a dump valve for the returning oil.

I am curious as to why you want to built such a capable splitter and then limit it with a low hp engine and limited pump pressure. As well as the added cost of a big enough control valve to handle the chosen oil flow just to build a 36ton splitter. what type of wedge design are you planning.

My cyl are also 4.5in bore, but I have a 2.5in rod and 30in stroke. I will also being using a double pump setup but 42 and 33 gpm combined total of 75gpm flow. My ports are 1in. My control valve is rated for 70gpm which is marginable for my splitter, and I will most likely be installing a dump valve for excess flow. I plan on running 3000psi for 53 tons splitting force, but will be using a 12way multi-split box wedge.. My pumps are capable of 3600psi and if need I can turn the pressure up until the wood splits or something breaks. Hp isnt going to be a issue with my build as I am planning for 190hp power supply.

 

[MattBanchero]

What size are the ports on your cyl, you will be dumping a lot of oil back thru the control valve on the return stroke. What flow is your control valve rated for. I havent done the math but guessing around 60gpm for return flow, might be more considering the size of the rod. Might want to do the math and think about incorporating a dump valve for the returning oil.

I am curious as to why you want to built such a capable splitter and then limit it with a low hp engine and limited pump pressure. As well as the added cost of a big enough control valve to handle the chosen oil flow just to build a 36ton splitter. what type of wedge design are you planning.

My cyl are also 4.5in bore, but I have a 2.5in rod and 30in stroke. I will also being using a double pump setup but 42 and 33 gpm combined total of 75gpm flow. My ports are 1in. My control valve is rated for 70gpm which is marginable for my splitter, and I will most likely be installing a dump valve for excess flow. I plan on running 3000psi for 53 tons splitting force, but will be using a 12way multi-split box wedge.. My pumps are capable of 3600psi and if need I can turn the pressure up until the wood splits or something breaks. Hp isnt going to be a issue with my build as I am planning for 190hp power supply.

My splitter is a variation on a box wedge...this is the third variation on the splitter assembly. I think I've finally solved the problem of wood packing in the wedge. The first few times I ran the wedge the wood pushed through beautifully with low pressure. Then scraps and gummy bark would fill up the gaps. At a certain point it doesn't matter how much power you have if the peice you're pushing through doesn't have the structural integrity to deal with the force. The wood crumples and expands in the wedge.

I think there is an elegance to running this monster splitter with very low pressure and power...that's where the engineering comes in. My first versions were skid steer attachments running as low as 1200psi, but once they jammed up they were stopped up with 4000psi. 64 ton didn't do it.

I have been looking and I think a double pump makes more sense. I'm going to run the splitter with auxiliary hydraulics first and then dial in the dedicated system for the splitter.

Having worked on my project for a long time your numbers sound crazy. 75 gpm is going to give you something like 10"/sec of extension speed and get the f*** out of the way for the retraction.

What size peices are you trying to get?

 

[ChoppyChoppy]

10" second isnt too horrible. That's about what mine is.