Objective: redesign existing pilot adjusting needle to regulate pressure. The timer cap that controls the needle:
http://www.williamspumps.com/corp/details/0,,CLI1_DIV26_ETI3168,00.html

I would like to know the following if you have had the experiences in this kind of pump design:

1. How many type of needle (pin) designs to control the pressure with a timer cap?  (As much I know, there would be "slope" needle (no seals o-ring required, but you have to tight very hard to seal), and "dent" needle (seal teflon o-ring is required, but teflon will cracks over repetitive dent contact)

2. If it is the slope type, how do I calculate the needle (pin) slope, thread versus, pressure regulators, and timer cap (turning knob) relationship? Does anyone has some formula or calculating methods to share?

3. Which design is the most efficient as far as pin design?

First, the page you're referencing doesn't have the 'timer cap' needle valve I think you're referring to.  It only shows a micrometer stroke length adjuster for the pump plunger.  I think you're referring to the MKVII type oscillating controller, which is one of a few different controllers Williams makes for these pneumatic metering pumps, and uses a needle valve to throttle the air/gas flow to the pneumatic cylinder, increasing or decreasing the stroking rate.  Are you referring to regulating the air/gas supply pressure (which would result in a very coarse adjustment in the maximum pump discharge pressure) or regulating the pump discharge pressure? 

Well, I can't be of any help designing a needle valve pressure regulator, you're looking for a valve designer, not a pump designer.  One thing I can tell you though, that needle that you're referring to has nothing to do with regulating the air supply pressure.  It adjusts flowrate, nothing more.

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