A 22gpm 2-stage pump like this one
https://www.surpluscenter.com/item.asp?item=9-7970&catname=hydraulic flows 7 gpm on the hi-pressure side @ 3000psi.
The formula is (PSI x GPM)/(1714 x % eff)= required HP
So, (3000psi x 7gpm)/(1714 x 85% eff) = 14.4HP required. So YES, the 18hp you have will work.
But, it is going to be REALLY slow. you are looking at 42 seconds to extend in high speed and 36 to retract in high speed. So a 78 scond cycle time:confused2:
On a positive note, with @ 700psi, you can develop almost 18 tons of force without even hitting low speed. But if god-forbid it does shift into high pressure low speed, you are looking at a blistering 30 inches per minute extend speed:laughing: Can you say "how about a cup of coffee while you wait"
And if you ever do need the full power of that beast, it will be in the order of 75-76 TONS of force. And Unless its a super heavy duty 12" beam, I dont think it is up to the task. You are going to need to build the thing like a tank.
All that said, I have two questions for you:
IS the 72" of length actuall required? or is it just what you have?
You should really consider selling that cylinder if the length isnt needed. And getting something more reasonable. I know it sounds cool to build that monstorous of a splitter. But it is going to be inefficent and not real practical IMO.