pump and motor size ?

[captjack]

Hello

We are starting a log splitter project and have acquired a 26x5x2 cylinder off a dozer.

I am leaning toward a 28 gpm pump to increase cycle time.

What size motor should I be looking for to run such an animal?


We might end up building something like this instead of a regular splitter with a 6 way wedge.

YouTube - the best wood splitter


its kinda of a neat idea - would like to see it on some knotty oak !

 

[captjack]

we are looking for fast cycle times with this splitter as well as power.

 

[J_J]

16 HP

 

[LD1]

There is no short answer. There are a few variables you need to consider first.

The formula is GPM x PSI divided by 1714 x efficency.

So the variables you need to consider are

1. What is the max PSI of the pump.

2. Is it a single stage 28GPM or a two stage???
If it is a 2 stage like this one Haldex Hydraulic Pump — 28 GPM, 2-Stage, Model# 1080036 | Pumps | Northern Tool + Equipment
Then the 28GPM would likely be at a reduced psi, something like 650psi. And the full 3000PSI would be at a reduced GPM, probabally around 4 or 5. (that website does not list the specs)

If a two stage, you would need to calculate both ways. But northern tool shows a 12HP motor as a minimum.

But if you want a single stage pump, It will require more HP.

28x3000=84000
1714x85% eff=1456
84000/1456= about 58 HP to run. I am sure this is not what you want. But it gives you an idea how to use the formula.

 

[captjack]

The more i look into this the more things come into play. First the valve for a 28 gpm pump are expensive ! we are going to make a log lift as well as a hydraulic wedge.

I was happy to go with a 22gpm pump but i think the 26x5x2 ram will not move as fast as I want it to.

is there a way to figure out cycle times ? if I can get away with the 22gpm pump it would save me a ton of money

thoughts ?

 

[LD1]

calculate the volume of the cylinder.

5/2=2.5
2.5squared =6.25
6.25 x pi x 26" length=510 square inches

508/1728 to concert to cu/ft =.29

.29 x 7.48 gal per cu ft = 2.2 gallons of fluid

then just a little math frome there using a 22 gpm pump, it would take 6 seconds to extend. slightly less on the return due to being less volume because of the cylinder rod. You can figure the area of the cylinder rod and subtract it from the total area and figure it exact if you want.

So you are looking ar roughly a 11 second total cycle time with the pump in "high" gear

 

[kennyd]

Jack, use some of these calculators to help in your decision: Baum Hydraulics Corp :: Spec Calculator

 

[AKKAMAAN]

And the full 3000PSI would be at a reduced GPM, probabally around 4 or 5. (that website does not list the specs)

All Haldex two stage pumps are flow rated at 3600rpm
This pdf have all the displacement data for all pump combinations...

Small gear displacement 0.465 cui/rev
Large gear displacement 1.395 cui/rev
High flow>>(0.465 + 1.395)*3600/231=28.98 gpm
low flow>> 0.465*3600/231=7.24 gpm

Low pressure adjustable between 400-900psi>>high flow power=6.77-15.23hp

Low flow/high pressure power at 3000psi=12.67hp

 

[LD1]

All Haldex two stage pumps are flow rated at 3600rpm
This pdf have all the displacement data for all pump combinations...

Small gear displacement 0.465 cui/rev
Large gear displacement 1.395 cui/rev
High flow>>(0.465 + 1.395)*3600/231=28.98 gpm
low flow>> 0.465*3600/231=7.24 gpm

Low pressure adjustable between 400-900psi>>high flow power=6.77-15.23hp

Low flow/high pressure power at 3000psi=12.67hp

You didn't figure the 85% efficenty into the equation.

Thus with that figured in, you would need 7.96-17.91 on the highflow and 14.9 on the low flow side taking 85% efficency into account.

 

[AKKAMAAN]

You didn't figure the 85% efficenty into the equation.

Thus with that figured in, you would need 7.96-17.91 on the highflow and 14.9 on the low flow side taking 85% efficency into account.

The total efficiency is 100% minus the volumetric losses and mechanical friction losses, added together. Volumetric pump efficiency is factor that depend on pressure and fluid viscosity. With very low pressure and high viscosity, efficiency gets closer to 100%


The pump rating is with out calculating efficiency...that's right, but you do not have to add more HP because pump is leaking internally (inefficient)....your 85% volumetric inefficiency factor will reduce flow out put....15% of theoretical flow will leak back to suction side.... That do not take extra HP....the only extra HP needed is for the mechanical friction losses, in bearings, pump gears etc.

You can use the efficiency factor to calculate the required pump displacement, to calculate a NET flow output...

 

[LD1]

The total efficiency is 100% minus the volumetric losses and mechanical friction losses, added together. Volumetric pump efficiency is factor that depend on pressure and fluid viscosity. With very low pressure and high viscosity, efficiency gets closer to 100%


The pump rating is with out calculating efficiency...that's right, but you do not have to add more HP because pump is leaking internally (inefficient)....your 85% volumetric inefficiency factor will reduce flow out put....15% of theoretical flow will leak back to suction side.... That do not take extra HP....the only extra HP needed is for the mechanical friction losses, in bearings, pump gears etc.

You can use the efficiency factor to calculate the required pump displacement, to calculate a NET flow output...

Makes sense. I have seen the formulas both ways. Some that acount for eff. and some that don't. I always calculate with the eff. cause that gives a little built in cushion. But I am never one to work something to its max. I'd rather go just a little bigger and let the motor live a long "easy" life.

 

[AKKAMAAN]

I'd rather go just a little bigger and let the motor live a long "easy" life.

Agree on that one....:thumbsup:

 

[Reg]

The more i look into this the more things come into play. First the valve for a 28 gpm pump are expensive ! we are going to make a log lift as well as a hydraulic wedge.

I was happy to go with a 22gpm pump but i think the 26x5x2 ram will not move as fast as I want it to.

is there a way to figure out cycle times ? if I can get away with the 22gpm pump it would save me a ton of money

thoughts ?

MANY times the "cycle time" (cylinder full stroke forwards/backwards) is just about irrelevant to "production".
Getting the wood TO the splitter and AWAY FROM the splitter are more likely to limit how much wood you can split in a day or half day.

I found a 5 inch diameter cylinder to be very desirable - cross sectional area being 25/16 times that of a 4 inch diameter, although obviously slower than a 4 inch cylinder run from any given pump.
I ran it from a 16 GPM pump on an 8HP engine.

The other thing I found was that with a 24 inch capacity when splitting 18 inch bolts I would take the cylinder back to maybe a 20 inch opening and a lot of wood "just busts open" when the wedge is barely 6 inches into it - so the USED stroke may only be about 8 inches, perhaps 10.

If I was doing it again I would use a 5 inch cylinder on a 16 GPM pump with 8 HP engine.
I really don't see any need for anything bigger or "faster".

Anything a 5 inch cylinder can't get through ? Maybe some weird burls ?
Maybe some weird elm ? Do you really want to BURN that ? (-:
For oak and maple I would figure on the 8 to 10 inch ACTUALLY USED stroke,
as I said cycle time is pretty much irrelevant.

 

[LD1]

Anything a 5 inch cylinder can't get through ? Maybe some weird burls ?
Maybe some weird elm ? Do you really want to BURN that ? (-:

Because american elm burns really well and is highly desired, at least around here.

 

[J_J]

Just a curious question about a log splitter. Has anyone considered using a large hyd accumulator, in the hyd circuit, approximately the size of the cyl. The accumulator would be charging during retract time, or rest time, and perhaps keep a full charge in the accumulator, before the next log serup. Would the accumulator increase splitting time, or, would it work at all?

There is a story behind this question, but I would like to hear some thoughts on this.

 

[LD1]

Just a curious question about a log splitter. Has anyone considered using a large hyd accumulator, in the hyd circuit, approximately the size of the cyl. The accumulator would be charging during retract time, or rest time, and perhaps keep a full charge in the accumulator, before the next log serup. Would the accumulator increase splitting time, or, would it work at all?

There is a story behind this question, but I would like to hear some thoughts on this.

Interesting question.

I think due to the complexity of the system, it would not be very cost effective. There are other alternatives that are more affordable to increase splitter speed.

But if money were no object I am sure it could be done.

A couple of obstacles to overcome though are

1. You would have to have some type of valve feeding the accumulator that would "kick out" once the accumlator has reached max PSI. Kinda like the valve that feeds the cylinder kicks out once the cylinder is retracted. That way, when the splitter is at rest, you aren't building 3000psi, opening the checkvalve, and just venting back to tank and heating the fluid up.

2. Trying to tee the accumulator in with the cylinder (through the valve) to feed the cylinder at the same time the pump is also trying to feed the cylinder would require a lot of complex plumbing, check valves, etc.

3. Another issue would be filling the accumulator. This could only be done at rest. If you try to fill it on the return stroke, it will cause the pump to kick into low stage to get the 3000psi, which would make the return stroke very slow. Not to mention, any flow taken away from the cycle to fill the accumulator will slow the cycle down.

So basically, In order for the accumulator to do any good at all, it will need to be filled with half or more of the cylinder volume @ 3000psi.

A 5" cylinder holds 2.2 gallons. So suppose you have an accumulator that will hold 1.1 gallon of fluid @ 3000psi. A typical 16gpm pump is 3.5 GPM on the second stage. This would take about 19 seconds just to charge the accumulator. If speed is your concern when splitting, you aren't going to wait 19 seconds when the ram is "home" just to charge the accumulator.

And one final thought of mine (I am sire I am missing some more negatives)
As the accumulator discharges its gallon or so of fluid, the pressure will start to drop off.

SO............What is the story behind this????????????????

 

[LD1]

Apparently this guy had built a homemade unit, and when he went to split the first log, the cyl extended so fast, and with great force, and shattered the log and almost killed him from the wood grenade pieces. He was hurt, but survived.

Although a hyd pump can pump maybe 10 GPM, it takes a full minute to do that. When an accumulator dumps it's load, it does that rather quickly. , taking into consideration hose size, etc. If an accumulator would burst with you beside it, you might be in trouble.

I guess it sort reminds me of those tire air tanks that let out a large volume of air to inflate a difficult tire.

If a large enough accumulator is used, I can see that happening bu only for the first peice of wood. After that, the accumulator would be about worthless if not given enough time to charge.

Our splitter is a 4.5" cylinder and an 11gpm pump. When splitting, there is very very little time when the splitter is actually at rest. So an accumulator would do no good at all. Bottom line is, the pump can only pump so much, if you take away from that to charge an accumulator, that will slow down the cycles. And if you have enough time at "rest" to charge an accumulator big enough to do any good, you probabally arent worried about speed anyway.

 

[DaveOmak]

JJ Morning, Question about accumulators.

Now I been reading about hydraulics. (still consider myself an idiot when it comes to hyd) Help me out with this. What I read said, "When the cylinder slows, for any reason, the pump is still pumping at design flow. Hoses swell and the pump starts cavitating and pitting occurs,(vane pumps I think) and damage results". The article states, accumulators will increase efficiency and reduce wear during heavy loading.
What am I missing between this thread and the stuff I am reading.
Thanks, Dave

PS: An accumulator will not slow down the operation at all. The pump is still pumping
at rated GPM.

 

[J_J]

IMO, an accumulator is used as a power supply however small. While a cyl take time to push using available fluid, the pump can only push so much. The accumulator can let lose a large volume of fluid rather quickly. In a lot of cases, it is used as an assist. If you want hyd to work fast, I can see where an accumulator can accomplish that. An accumulator can store energy and use it after the hyd system has shut down. A brake system might use an accumulator in an emergency to apply the brakes. I had even thought about using an accumulator for an emergency stop on my PT. I believe the new models did that. Some hyd motors have spring applied brakes, and with hyd system off, they use a pump and accumulator to release the breaks.

In the military, we has an engine starter that you had to pump up, and when the pressure was right, you open this valve, and the hyd motor started the engine.

There are good uses for a accumulator, but you have to be careful about your design, and ramifications of bad design.