SpudFiles

I have so far built 2 air guns and both of them are pretty basic , the first one is just a fizzy drink bottle attached to a pvc pipe with a ball valve (could reach 130 Psi but wasn't very powerful) and the second was similar with a fizzy drink bottle as an air chamber but a water hose gun as a valve. Now I want to actually make an air gun that is really impressive and I have a few questions I would like to ask. Is it possible to get multiple shots out of an air chamber with a sprinkler valve? Whats is more important to get longer shots, Psi, Valve or C:B Ratio? And I also found a link to a website with plans for a homemade Paintball gun and I was wondering if it would be effective: here is the link http://www.gizmology.net/pbm.htm.
Thanks.

Hard 2 Hit wrote:Is it possible to get multiple shots out of an air chamber with a sprinkler valve?

Assuming your chamber is big enough, sure.

Whats is more important to get longer shots, Psi, Valve or C:B Ratio?

They're all important factors. Double the psi and you double the power, it's as simple as that. As to valve performance and chamber size, the best advice I can give to (other than a lot of trial and error) is to download GGDT and model your launcher virtually before commiting to actually making a project, by playing around with the parameters you can maximise your performance and efficiency.

http://www.gizmology.net/pbm.htm

This is what we call the "blow-forward breech" design that has been built successfully by a few members on here, myself included

I'm deciding between the Blow-forward breech and making a piston valve, what do you reckon will have more power, and I was wondering if i could merge the 2 seeing as the breech seems to be just a loading system. Also can you make small piston valves such as a 15mm because PVC is super expensive over here (something like $50 for an 100Mm Cap).Btw Thanks jackssmirkingrevenge that info is extremely helpful.

Another Kiwi!

Welcome


I know what you mean, the prices here are bloody insane. You can make 50mm cannons reasonably cheap, they're only about $10-15 a fitting. But mine still end up costing around $300-400:

http://www.spudfiles.com/forums/v-a-l-p ... 14702.html
http://www.spudfiles.com/forums/viewtop ... tml#100616

JSR is right, model your launcher before you build it. I actually drew my entire gun on a piece of paper, a life-size drawing. Anyways, you should actually put a blow forward breech on, with a sprinkler valve.
Experiment with GGDT as well.

Hydra wrote:JSR is right, model your launcher before you build it. I actually drew my entire gun on a piece of paper, a life-size drawing. Anyways, you should actually put a blow forward breech on, with a sprinkler valve.
Experiment with GGDT as well.

I have an A3 folder and two A3 sketch books full of stuff for my recent cannon the V.A.L....but that was for a school project

Hard 2 Hit wrote:I'm deciding between the Blow-forward breech and making a piston valve, what do you reckon will have more power, and I was wondering if i could merge the 2 seeing as the breech seems to be just a loading system. Also can you make small piston valves such as a 15mm because PVC is super expensive over here (something like $50 for an 100Mm Cap).

As you said you can't really choose, the blow forward breech is a reloading, not firing mechanism. There are ways in which it could conceivably be a firing mechanism too, but it's driven many a desperate fabricator to the very brink of sanity trying to make it work

You can make piston valves as small as you like, it's just a question of seeing what materials are available to do and working around it. Do get in touch with MrCrowley, fellow kiwi, experienced builder and always ready to help

That a piston valve would be less efficient than a sprinkler valve when used with a blow-forward breech loading system. Also wouldn't it be a waste making a blow-forward if pistons can only be shot once (Correct me if I'm wrong) because you'd have to refill the air chamber anyway.

there are semi auto pistons..

Most pistons are designed to dump all the air in the chamber, but if you have a large enough chamber, a pilot valve that opens momentarily and a piston that reseats quickly it's very possible to get more than one shot out of them. If you just want a high powered single-shot launcher, it's easier to leave out a reloading breech altogether.

Can I fill a piston valve with a bike pump (Max Psi 100) or wouldn't that close the piston? Would it be hard to make a piston valve that reseated or would it be too hard to do with just basic resources and budgets.

You can reseat a piston with a bike pump, and o-rings would help doing that, but if it doesnt reseat, you could always add a spring behind it.

Assuming your piston is a tight enough fit and your pilot volume is kept to a minimum, a bike pump should be more than enough to close it. As to a reseating piston, with my projects I find that I can get multiple shots just by "tickling" the pilot valve, again what's important is small pilot volume which you might want to assist with a spring.

Is this a good piston?, a wooden cotton reel with bike inner tuber rubber for the sealing edge and a bolt down the middle with a washer etc, and I was also wondering what a good bumper would be.

As long as it's a tight fit in the pipe you intend to use it in - tight as in when you try to blow air past it you get blue in the face, but at the same time you can still push it in the pipe with one finger. As to a bumper, a few rubber disks (maybe cut out of the same inner tube) will suffice.