@ pto pump on the same shaft like a double pump?

[Millet]

Hi,

I want to build a firewood processor, And I wonder if I can put two PTO pump on the same shaft to have like a tandem pump.
I need to have two pump to run the hydraulic chainsaw, the splitter Ram, the log infeed, split wood conveyer...

Also I think I will not use a 2 stage pump for the log splitter. I don't think that the commercial model use one.
What do you think?


This my first post. I was born in France so English is not my first language...


Thank you

Millet

 

[RNeumann]

I’m confused why you would add the complexity. One pump sized to the HP output of the PTO (or your needs) means one reservoir and should be cheaper and easier to make and maintain.

If I’m missing something can you further explain your thoughts behind two pumps.

 

[Millet]

Because I have many actuators: cylinders and motors. And don't want to split my flow many time, because I think , correct me if I'm wrong, that
each time you divide your flow you loose power and create heat resulting of the friction . I see many firewood processor using 2 to 3section pump, I think that's why.
Each actuator need different psi and gpm so I thought it would be easier and cheaper (less valves...) in the long run to have at least 2 pump.
No?

 

[MossRoad]

Yes, you can stack pumps. My machine is a hydraulically articulated loader. It has three pumps (and one reservoir). One pump (the variable volume drive pump) is in the front of a 25hp Kohler gas engine, and the other two (PTO and aux hydraulics) are stacked on the back of the engine.

Newer models have all three pumps stacked on one side of the engine.

Not sure why you wouldn't want a two-stage pump for the splitting ram. It would really decrease the cycle times, yet still provide high power for tough wood.

 

[Sawyer Rob]

Not sure why you wouldn't want a two-stage pump for the splitting ram. It would really decrease the cycle times, yet still provide high power for tough wood.

How does it "decrease cycle time"?

SR

 

[4570Man]

How does it "decrease cycle time"?

SR

I think you already know the answer. A 2 stage pump does nothing all in itself. You can get a lot more GPM out of the same motor with a 2 stage vs a single stage pump. If you have enough hp to get the flow and pressure you want with a single stage then there’s no point. It’s going to take about 35 hp to push 20 gpm at 2800 psi. If you drop it to 20 gpm at 700 psi which is about where the 2 stage switches over you only need about 10 hp. If you drop the flow to 5 gpm at 2800 psi it’s still under a 10 hp load.

 

[MossRoad]

How does it "decrease cycle time"?

SR

You figure it out.

 

[Sawyer Rob]

You figure it out.

It was YOUR statement, I thought maybe you could enlighten us how that works?

SR

 

[Millet]

In fact I wonder if the shaft of the pto pump will be strong enough to drive 2 pump. Do you think that 2 X 15gpm 2000 psi max pump will impose
the same resistance at the pto shaft that 1 X30 gpm 2000 psi pump ?

In other word if you have many pumps on the same shaft do you need to add the
max pressure of each pump for shaft strength calculation ?

Exemples : pump 1 at 1400 psi. pump 2 at 2000 psi = shaft "torque" = 3400psi or 2000 psi ?



I didn't intend to use a 2 stage pump because I will use the tractor pto to drive the pumps and a 2 stage pump need higher rpm to work correctly.
And the flange need adaptors. I thought the simplier will be 2 pto pumps on the same shaft.

Also looking at commercial firewood processor, I think they usually didn't use this kind of pump.

I have a 80 hp tractor so I think I have enough to use a single stage pump with speed and strength.

 

[oldnslo]

Millet,
A few things for you to keep in mind.
1) Yes input torque is additive when you have multiple pumps be driven by a common input shaft. You must add up all of the drive torque to ensure the shaft is strong enough.
2) What RPM does your PTO operate at? 540, 1000 or some other speed? I believe some foreign models have ranges like 750 or 960. Most pumps operate better at around 1,800 to 2,500 RPM or possibly even faster so you may require some form of speed increaser. Some pumps will not operate properly below 600 RPM. Verify the operating range of your pumps.
3) Yes you are correct that flow dividers create heat and multiple flow dividers in the same system may also cause instability problems.
4) If considering chain or belt drive make sure that your front pump bearing will with stand the side loading from the belt or chain. Some pumps have special bearing options for this side load.
5) Like others have stated it is usually better to run multiple pumps for system like this VS one larger one.

Good luck