SpudFiles

Ok, a two foot long 2" tank with an endcap and 2"->1.5" reducer bushing then a rainbird 1.5" sprinkler valve (can someone help me find where to get it?) and then 3 feet of 1.5" pipe. This should all be pressure rated so I can launch at 100 psi right? One last thing I need to know is, where should I put the schader valve and the psi gauge, also what is the difference between SCH40 and SCH80 and would it matter if I only want to shoot up to 100 PSI?

Thanks in advance and here is a picture.

Sch 80 and Sch 40 use diferent adapters but both should be able to handle 100 PSI, just don't go above it. Sch 80 is a little thicker but still dont go above 100 PSI. Make your barrel shorter, to about 20" for a good 2:1 ratio. Also, move the sprinkler valve as close to the chamber as possible.

The rating on 2" sch 40 is something like 320 PSI; there is no need to worry about pressurizing it to 100. However, sprinkler valves are typicaly only rated to about 125 PSI - so 100 is a safe limit.
AND DON'T MAKE YOUR BARREL SHORTER! You'll only lose power.
Oh, and sch 80 fittings do fit on sch 40 pipe.

ok thanks leadbath, very helpful

I regularly use 130psi with two in sch 40 , the fill valve is in the endcap but that's just a matter of preference.
If I had 2ft of 2" pipe ,I would use 4 or more ft. of 1.5" for a barrel.
If you are new at pneumatics I would stay with the 100psi recommendation
until you are sure it is built well and holds together well.

boilingleadbath wrote:AND DON'T MAKE YOUR BARREL SHORTER! You'll only lose power.

I'm still a n00b at this, so forgive me for questioning....

If the barrel is too long and not shortened, as recommended by boilingleadbath, isn't it possible for the potato to still be in the barrel after the combustion is complete, creating a vacuum behind it as the gasses cool (volume decreases as temperature decreases, Charles' Law), thus adversely affecting the muzzle velocity?

Yeah, but the potato will be out of the barrel way before that happens. You may want to check out Burnt Latke's C:B ratio tests.
http://burntlatke.com/15cb-testday.html
and
http://burntlatke.com/15cb-data.html

eh... I was of the understanding that this was a pneumatic, not a combustion.

Thank you. I feel really stupid. Again.

Glad I added a disclaimer....

BLB, wouldn't the same thing apply to a pneumatic? I mean you could get a lot more barrel out of a pneumatic, but it still has the same prinicple in mind.

i guess it is just a matter of getting the barrell just the right length, where the pressure in the chamber is just enough to keep pushing but wont slow the spud down.

I was thinking again last night (dangerous....), and it occurred to me that the same principle would apply, but less so than a combustion gun. After the combustion is complete, friction in the barrel would start to slow it down.

Sch40 and 80 are jsut different thicknessess of pipe.
Sch40 holds up better to external forces than sch80.
But 80 can take more internal pressure.
Both work fine in most spudguns.
Your design looks fine, but make sure its upgradeable to sprinkler valve.

I wouldn't Use 6 inches of pipe between the Valve and the chamber, Just use a Threaded 1.5" male to None threaded 2 inch female.

I didn't know they made 1.5" sprinkler valves?!?!?

They make sprinkler valves in all kinds of sizes.
If I had the tools I could make a 4 in one and it would kill a piston valve.