Crank shaft design

You are building a 4000 psi triplex pump from scratch? Uh you do know there are companies that make these?

I don't mean to be rude, but if you are asking this question here, you have no business trying to design such a part, and if you carry on it very likely will get someone hurt or killed.

If you wish to learn about pumps, then the following would be a good place to start.

http://www.amazon.com/High-Pressure-Pumps-Michael-Gracey/dp/075067900X/ref=sr_1_1/105-6421074-1426024?ie=UTF8&s=books&qid=1190569164&sr=8-1

http://www.amazon.com/Pump-Handbook-Igor-J-Karassik/dp/0071460446/ref=pd_bbs_1/105-6421074-1426024?ie=UTF8&s=books&qid=1190569247&sr=8-1

Please go and look at the following web site and see if the need is so strong that you might remove your genes from the world pool!

http://darwinawards.com/

If not, go and buy from professionals.....

Remember that 4000PSI is a deadly amount of air pressure, that can be likened to several sticks of dynamite at very close quarters.....

OPI, National Oilwell-Varco and others make these all day long and you can buy them off the shelf. Are you looking to rip off their design and make a clone of it?