Are you talking about pipe diameter? As far as I am aware, 2" pipe has the same inside and outside diameter in America and Aus/NZ. Are you refering to my how-to btw?
What are spud bux anyway? Rating?
Search. Please. 10000 topics on this.
edit:
Tcoz370 wrote:but how does air get behind the piston to force it shut against the barrel?
It seems that you have done minimal research on piston valves. We're not going to spend 4 pages telling you exactly how they work, so brush up on the operation and construction of a piston valve, then come back and ask us some more important questions that can't be answered by simple researching.
Tcoz370 wrote: then i guessing u have a blowgun valve on the piolet side
This is a very common misconception that I try very hard to get rid off. A blowgun will not be a sufficient pilot valve for any piston 1.5" and above. Even a 1" piston i'd recommend a ball valve. Sure you can pilot 1.5" and above sized piston valves with a blowgun but you'll get pretty bad performance.
Even if performance is average, a similar sized ball valve or better yet, a sprinkler valve, will boost performance considerably. With an o-ring sealed piston using a 1/2" ball valve, i'd say that it would improve performance around 20% over using a blowgun depending on a few factors.
jackssmirkingrevenge will have no problem telling you that a piston can be piloted with a schrader valve (maybe not a piston this big), but it is important to stress that a bigger pilot valve is always better than a smaller one. Though it is still very important you make your piston have a very good fit inside the piston housing, it doesn't have to be o-ringed.