How big of a pump can I run off a Kubota L3800.

[4570Man]

I'm wanting to run a 21 GPM 2500 psi pump off a L3800 PTO. I'm reading significantly varying numbers on the power required. On the low end I can do it. High end I won't be able too. Should I take it down to a 16 GPM? I really don't want to because I'm running a 5" bore cylinder and it'll be slow.

 

[motownbrowne]

I'm running a 21 GPM pump on my TC 29. You've got quite a bit more HP than me. It does fine on my TC, but I had to set the relief at about 1700 psi. You might not get the full 2500, but you should be close.

Building a splitter?

 

[oldnslo]

(GPM times PSI) divided by 1500 will get you close to HP required. If using a Hi-Lo pump you should have more than enough HP.

 

[boggen]

below link has some calculators and basic info
Surplus Center
direct link to a calculator
Surplus Center

 

[LD1]

HP = (GPM x PSI)
.............(1714 x efficiency)

Usually use 85% for efficiency. So....21gpm x 2500psi = 52500

1714 x 0.85 = 1456 (close to the 1500 that oldnslo eluded to)

52500/1456 = 36HP required at the PTO.

If you are building a splitter though, it isnt very often it peaks the pressure.

With 30HP at the PTO, you can reverse figure it. You can sustain 2081PSI at 21 gpm

Or....17.5gpm is the max you can push at 2500psi

 

[LD1]

So....another poster mentioned a splitter. Is that indeed what this is?

 

[teg]

...direct link to a calculator
Surplus Center

Did you see this in your link: "Calculated for electric motors. Double this figure for gas engines." I wonder what the figure is for diesel engines???

 

[4570Man]

So....another poster mentioned a splitter. Is that indeed what this is?

Yes, and I'm wanting to avoid using a 2 stage pump like the original plan.

 

[LD1]

You have a few options I'll run by you based on 30HP at the PTO. (assuming a 2" rod size and 24" stroke)

#1. 5" cyl w/21gpm pump. You are gonna get 2100psi max.
...............20.5T max, 10.8 second cycle time
#2. 5" cylinder w/16gpm. Gonna be able to get full 2500psi.
................24.5T w/14.2 second cycle
#3. Drop to a 4.5 cylinder and run 16gpm pump. Will get the full 2500psi
..................20T with a 11.2 second cycle

This is pretty similar to what you would get with the 5" cylinder and 21gpm setup you are contemplating. But cylinder an pump will both be cheaper and a better match for your HP.

#4. Same as #3 but with 16GPM you could actually push up to 2700PSI. Same cycle time but would give 21.5T power. Actually more than you would be able to get out of the 5" / 21gpm combo

 

[4570Man]

I've already got the cylinder. I bought it at a scrap yard for 25 cents a pound. It's a 5" bore 22" stroke. The ram is pretty big but I haven't measured it. I'd say around 2.5". The other question here is would the tractor put out more than 30 hp for a brief period? It'll be sitting stationary while splitting wood. I could run it off the front of the CTL and get 40 gpm ( not really because I wouldn't spend the money on high flow connections and hoses ) at 3500 psi but that's not the most cost effective solution because it cost me $20 an hour. The tractor only cost diesel fuel and less of it.