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Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: jrrdw » Thu Mar 12, 2009 1:53 pm

jeepkahn wrote:
jrrdw wrote:Yea, just look at what they have all ready downloaded onto your computer.... :twisted:


???? Was that directed to me???


Yes, I was joking..... :twisted:
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Unread postAuthor: MrCrowley » Thu Mar 12, 2009 7:40 pm

jeepkahn wrote:1.5" pvc is rated to 330psi, and the chamber will prolly only be 6" long and after deducting 1" from either end where the fittings effectively double the thickness, there will only be 4" of exposed 1.5" sch40, so from a materiel strength/failure aspect, 250psi should be fine... when the boys are using them I'll have a pop-off installed to prevent overpressurization...

would I take a 4ft long piece of 1.5" sch40 to 250 psi??? prolly not, but on a small chamber, it should be fine...

Remember it's not only the pipe that can fail, but the joints. Personally i've had two failures with PVC pipe, both have been because of the joints. I wouldn't trust PVC solvent welded joints to 250PSI.
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Unread postAuthor: ALIHISGREAT » Fri Mar 13, 2009 2:50 am

I second MrCrowley's comment, the PVC cement i have is only rated to 16bar - 232psi.
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Unread postAuthor: dudeman508 » Fri Mar 13, 2009 12:38 pm

You could drill holes and screw your joints together
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Unread postAuthor: MrCrowley » Fri Mar 13, 2009 2:56 pm

dudeman508 wrote:You could drill holes and screw your joints together

Could cause fractures, probably lower the rating a fair amount too.
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Unread postAuthor: jeepkahn » Fri Mar 13, 2009 7:47 pm

I'm not sure where you are finding "your" ratings for cement/primer, but according to the stuff I'm using it is supposed to be rated to 100% of the pipe/fitting rating... And unless I'm missing something, pressure rated fittings are designed with solvent welding in mind, If a properly welded joint can't handle the rated pressure then by default they would have to decrease the rating of the pipe to not exceed the joining method... ratings have to be based upon the weakest link, and I would imagine that the rating on the pipe is more a reflection of what proper joints would handle more so than the pipe itself...

Sorry it took so long to respond, but I wanted to do my homework first...
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Unread postAuthor: King_TaTer » Fri Mar 13, 2009 9:58 pm

Hmm, well that explanation makes sense in a theoretical way jeepkahn, but I'll let you know It's very bold of you to take PVC to such pressure(except for someone just recently taking up the hobby). There are so many variables involved such as: An unseen error while solvent welding, a faulty/defective valve, improper appliance of Teflon tape to threaded joints, warped or weathered pipe witch voids the rating... the list goes on.

Also if you don't already know that rating is for water pressure, and according to my knowledge air pressure behaves differently than water pressure. Water has surface tension and air doesn't while under pressure. Water also has a much bigger molecule than air. I'm sure someone could better explain this than me and correct this if my statement is wrong.

Then again I have no clue about your background, and your respect for safety. I don't mean to be the Negative Nancy :? but I'd also dislike feeding the media with another spud gun related injury.

My point is that the risk is too great. If you must build one then I would consider using a length of metal pipe as the chamber, and substitute anything else you can with metal. Even after this there's still risk, but there's always some risk :wink:

Sorry to rant but I wouldn't want you or your kids to be injured when it could have been prevented. Thanks for reading, good luck, TaTer
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Unread postAuthor: jeepkahn » Sat Mar 14, 2009 8:30 am

I appreciate everyones concern and it's not being taken lightly...

Since most people on here don't know my background I'll touch on it slightly before I continue with the pvc discussion...

I'm a 39yo Service manager of a powersports dealership, I have built and raced motorcycles and atv's for most of my adult life, I'm a certified structural welder(not pipe rated yet), I have way more intelligence than actual classroom knowledge, but I do my homework when it comes to subjects I'm not fully learned in, and I have the utmost respect for things that can main/kill me or others...

Now, the kids aren't even allowed to play with their airsoftguns wihout my supervision, and as stated before when they are using these pb guns I will have popoffs installed and filling of the chambers will be done by me to no more than 100psi... the only time these guns will see more than 200 psi is when I'm "playing" with them and the filling will be done with a bicycle track pump (so there won't be any "shock" pressurization), also the chambers will only be 12"ci (but I still wouldn't want a failure), And the chambers will also be sheathed in kevlar/nomex fire hose...

And as a point of referance, my 2"x 36" chamber coax has well over 200 shots fired with 180+psi...

Heck, no bigger than the chambers are gonna be, I may just use galvanized for the chambers...
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Unread postAuthor: inonickname » Sat Mar 14, 2009 9:13 am

Jobs aren't always the greatest things to boast about (we have people here who work with the military and weapons (dhall....) but I'm sure most people will be able to appreciate that.

Of course there would be exceptions, but you won't get "shock" pressurization through a small QD or schrader as it is.

Another factor you should take into consideration is wear and tear..giving plastic things to children never ever improves their lifespan, so the galv. fittings aren't that bad of an idea (they'll give the kids more exercise as well).

Just be careful because even if the cement holds abuse and the elements will not help PVC-take good care of them.

What Tater means is that PVC is meant for water- water will not compress (or very little) meaning it holds near no energy and there will be little damage on failure. This also applies to things like pressure washers- it doesn't compress the water to a pressure, but it can move water against that force.

Or simply, water will do less damage on failure.


It's up to you to exercise what precautions you see fit, but if you use PVC take extra care to make sure they aren't dropped, thrown etc..and that there put out of the weather after finished.. and so on.

Good luck
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Unread postAuthor: jeepkahn » Tue Mar 17, 2009 2:48 pm

Slight design change for the boys' guns, for simplicity sake, there going to be 3/4" qev valved, using the chamber as the stock, and they won't see more than 100psi (fyi, the boys are 10 and 12)...

However, since I've got 36 feet of pb barrel left, I'm going to build the hipres one for me using copper for the chamber and valve, I decided to go this route when I whipped together my first copper gun this morning...

It's a 1" chamber x .5" barrell coax, chamber is 24" long barrel is currently 5ft long, but I'm going to shorten it and get my brother the woodwqorker to bore out a wooden staff, then I'll epoxy the gun into wooden "cane", and then I'll use bondo/epoxy or some such materiel to shape a handle... Voila, walking cane hipres coaxiel...
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