sprink break proj, need some help

[grock]

much to the horror of my airsoft buddies, i am building a 3" bore cannon over sprink break. im thinking of using 2 4", 5' chambers, feeding a 5-6' 3" barrel. i had a couple questions. first off, should i use one valve fed by 2 chambers, or two valves T'd into the chamber? second, what sixe of T do i need for a piston valve that feeds a 3" barrel? third, thats the best material for making a piston of that size? fourth, whats good bumper material? and fifth how far is does the barrel need to go into the T?

any and all help is appreicated.

also, i am NOT planning to shoot my airsoft buddies with this cannon, becasue that would hurt like a b***h. but THEY dont know that

[inonickname]

Well I did see somewhere somebody using an 'X' fitting rather than a 'T' and creating a barrelsealer with it- A.K.A using two chambers. If you wanted two chambers you could go down that route.

[c11man]

first of all what do you plan to shoot with it?

this will determine need for one or two valves. most cannons are only single valved and are still very powerfull only cannon that are extreme preformace usualy use two vavle this size

as for the tee you need a 4 inch tee

[grock]

cool. im actually going to shoot water bottles, but im going to make some interchangable barrels eventually. is wood good enough to make a piston out of? im more limited by time/money then technology, have acess to a pretty high speed metalshop.g

[jook13]

3 inch schedule 40 couplers fit NICELY in four inch sch 40 pipe. That is what I did for my 3 inch bore cannon. For a Bumper I used a half of a nerf football and a thick rubber ring I found that fit good. Get creative with the bumper.

I dont know about how far into the tee is best, but mine worked pretty good at about 1/3 the way into the tee. A few people said it should have been closer to the middle.

To tell the truth I think that one chamber would be all the power you need and it would be much cheaper and simpler to build.

[grock]

yah, i guess so. but two canmbers would be much more beastly, and be sort of like a built in stand. then again, my homedepot gift cards can only take me so far; i dont have much real money

[jook13]

I havent seen a whole lot of home depots that sell pressure rated PVC above 2 inch. You are damn lucky if yours does!

yah, i guess so. but two canmbers would be much more beastly, and be sort of like a built in stand. then again, my homedepot gift cards can only take me so far; i dont have much real money

Its your cannon. do what you want. The built in stand is a nice feature.

[grock]

well, thats a nastily useful piece of information. are you saying that mine most likely sells that foam-filled stuff?

[jook13]

Read the side of the pipe. If it says anything like "nsf-pw" or anything about rated to a certain abount of pressure you are in the clear. I would steer clear of stuff that say "nsf-dwv" or not rated for pressure.

Read this:
http://www.spudfiles.com/spud_wiki/inde ... _Rated_PVC

[grock]

ahh ok. most plumbing stores should have pressure rated stuff right? the only reason id perfer homedepot is becasue i dont have alot of real money

[inonickname]

Erm... Doesn't "nsf" denote a pressure rating, and 'pw' denotes potable water - aka water you can drink?

Ignore if it says DWV or PW, you're in the clear if it has "XXX (pressure) psi @ XX (temperature)" stamped on it.

Edit: it should also have the thickness (schedule- Sch. 40,80,120 and so on)- asides from the pressure rating you probably want 40 or 80 for higher pressure.

Edit2: I was wrong and correct..

Drain Waste Vent (DWV) - A designation by the NSF (National Sanitation Foundation) that means the item is approved for drain, waste, or venting applications. By nature, DWV does not require a pressure rating, but some DWV pipes are rated for pressure.

[c11man]

ionickname only a rare few fittings have a rating on them in psi so looking for a fitting with a psi figure on them would be useless.

quote from the wiki
Fittings:

To find out if a fitting is pressure rated, it should have 'NSF-PW' written in raised text, it may also have Sch 40 (or 80,120 etc) on it. Most American fittings don't have a pressure rating on them, but if they have NSF-PW ("PW" stands for Potable Water, which, by nature is under pressure), you're okay, it will be pressure rated.

sorry dont know how to quote yet

you are right about wanting to look for a xxxpsi on pipe but not fittings. on fittings you want nsf-pw.

[inonickname]

Oh sorry, I was talking about pipe rather than fittings. But yes, seen as your mains water varies from 50-150 psi it will be rated for that easily..but keep in mind that's water that gives better fail characteristics than air, so don't overpressurize.

Over here we have pn (pressure number) or class. The lowest rated fitting available locally is rated at 18 bar, which is very nice.

[Lentamentalisk]

Even if you were to find pressure rated fittings and pipe that size, you would be looking at hundreds of dollars. For example, a 3" PVC tee, rated at 150psi (McMaster part number 46885K158) costs $56

edit: and it comes with a warning:

WARNING
Never use plastic pipe fittings with compressed air or gas.

but still, we do that all the time, as you can see...

[c11man]

holy crap your prices are WAY too high. I have never know mcmaster to a good a good source for pvc fittings. the best place i have found for pvc fittings that are pressurerated is www.flexpvc.com. here you can find a 3inch sch 40 pressurerated tee for $6.22. All of the fitting on that site are pressure rated unless noted plus they have way more fittings than they have up on the site. to see if they have a fitting that you need just give them a call.

EDIT: to find this tee easily just put 401-030 in there search box. Also you could buy a box of 10 tees from flexpvc.com for less than the one you found on mcmaser

EDIT: Plus you have a threaded tee witch away cost more and you dont need a fitting rated for maximum pressure

If you look again it does say "ASTM Specification
ASTM D1784, ASTM D2466"

Which, like mark says, means the fitting is rated as high as the pipe is.

It says its not rated to maximum pressure. It doesnt say it is not to be used with pressure.

If mark is right, im im almost certain he is, then the fitting is safe.

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