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Double PC WBL

Posted: Sun Apr 26, 2009 4:53 am
by Roboto
Would this concept work, and if this has been brought up I've searched everywhere on every forum to no results.

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5-6' barrel 3" (may be changed when Ben finishes his BAGS research :D ) reduced to a 1.25-1.5" PVC or metal ball valve (cost prohibitive for 2- easily 20$ for metal around here), over under design so 2" elbows and 2" PVC pipe for elbow communication, first chamber will be smaller than first and be 2" pipe- probably 1-2'. This leads to a second ball valve at 1.25-1.5" adapted to 3" PVC 4-5' for the main chamber.

Goal: Pressurize both chambers at once with BV1 (FC bv) closed and BV2 (PC bv) open. Close BV2 and top off the main tank (this is give or take to my knowledge...I'm assuming pressure will tend to equalize leaving less in the larger space) Load and open/close BV1, fire.

The tricky part that I am uncertain about: Open BV2 with BV1 closed...equalize pressure from the main tank for another shot? If possible, this is the main goal for multiple shots, although I doubt after shot two enough pressure will remain to move anything. An alternate would be for me to leave BV1 open and use BV2 as another FC. Of course, this method would lend the pipe to being more equal in length and probably 2"-3" throughout.

I have heard it is a good idea to have the pressure chamber(s) at a larger diameter than the firing chamber. If this is indeed the case, I will make the barrel 2" and the PCs 3"; 3"-4" is not in my budget.

Re: Double PC WBL

Posted: Sun Apr 26, 2009 11:07 am
by cantab
I think you'd suffer severe power loss. If the two PC's are equal size, then if they hold the same pressure the second shot has half the pressure behind it of the first. To make them equal the second PC would have to hold twice the pressure.

Generally a better option is to use a high-pressure-air tank, and a regulator. That can hold enough air for many shots. The drawback is it's not cheap.

Re: Double PC WBL

Posted: Sun Apr 26, 2009 3:43 pm
by Roboto
I have a portable air compressor if that means anything..

When you say regulator my brain takes a dump.

Re: Double PC WBL

Posted: Sun Apr 26, 2009 4:24 pm
by Specter
I think you would have trouble handling a 5-6' 3" barrel. 3" PVC isn't too light, and 5-6' long seems overkill. my 4' barrel on my WBL didn't work too well.(but i have a feeling it was due to my PC being only 1 foot) Farthest I was able to shoot a balloon was around 75 feet

Re: Double PC WBL

Posted: Mon Apr 27, 2009 12:02 am
by C-A_99
The second PC's pressure will be cut in half when you switch to it. The second shot won't shoot like the first because of this, it will behave differently due to lower pressure and higher air volume. Its better to go with conventional muiti-PC designs where each chamber is seperated from the others.

A regulator basically does what its named to do. Say you have a 1000 PSI tank attached to the regulator, which is then attached to a 1ft long 3" PVC chamber. You set the regulator to 80PSI or so, then release it to shoot. When the firing valve closes (don't use a ball valve as a firing valve, or air will be wasted), the regulator allows the air from the high pressure tank to flow into the lower pressure chamber. If you set the regulator too high, the PVC tank would be destroyed.

Re: Double PC WBL

Posted: Mon Apr 27, 2009 12:39 am
by Roboto
I think that may be outside the scope of this project. I do not have anything capable of pressuririzing or holding pressurized air up to those numbers.

You do make some good arguments, though. Thank you for preventing my wasting of time and money.

Is there anything I can do with a portable compressor long of just recharging after each shot?

Re: Double PC WBL

Posted: Mon Apr 27, 2009 9:35 pm
by cantab
"conventional muiti-PC designs where each chamber is seperated from the others"

By that, would you mean that each PC would have its own valve? That could actually work quite well, though might make for a physically bulky weapon.

Re: Double PC WBL

Posted: Mon Apr 27, 2009 10:08 pm
by Roboto
That would put it in the same class of Monster XL almost. That is double the pumping.

How high do those 250 PSI 12 volt compressors actually go? It might be easier to just fire and repump it.

I'd still use two pressure chambers in the conventional design, even though in the heat of battle it may be awkward to fuel.

Although this would be pretty amazing looking in a field setting.

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Yes, I did 3D in PVC designer. Believe.

I would probably use a series of T's or Y's if I did this, along with elbows. IF all else fails and I need to make it this way.

Re: Double PC WBL

Posted: Wed Apr 29, 2009 11:01 pm
by C-A_99
The air canisters and regulator would be the only parts that require the ability to withstand high pressures. However, you will also want to develop an air driven loading system if possible if using one of those configurations. Having to do this, as well as the costs with replacing air tanks is the main problem here; finding the parts is the easy part. (except for the parts on the air driven loading system)

Heres a previous design made 2 years ago that you will likely find to be helpful. http://www.isoaker.net/isnet/topic2564.html

Also, theres no need for thick pipe after the ball valves before the firing valve. Keep it at 3/4" or 1" from the PC valves to the firing valve. I recommend 3" for the PC's, while the barrel can be done as you see fit, 2" or 3". You can also design the barrels to be interchangable.

The breech is a pretty nice addition to speed up reloads. However, I have yet to be able to make one myself that is like the above. If you can find a way to do it, by all means, go for it. Make sure it seals well.

Firing valve. A custom built piston valve or a modified sprinkler valve are the best options.

Piston valve concept: http://sugarmtnfarm.com/snowwolf/images ... uncher.jpg

How to mod a sprinkler valve: http://www.spudfiles.com/forums/viewtopic.php?t=305

If you insist on the ball valve for ease of building, I'd recommend a PVC valve with a built torque arm, such as the one shown in this article. http://www.sscentral.org/homemade/supercannon2.html A metal valve also works, but it seems that plastic works better with plastic, and a custom torque arm (instead of the one that comes with the metal valve) can be made longer.

Look around the site and gather some ideas and concept before building. You'll be glad you did.

Re: Double PC WBL

Posted: Thu Apr 30, 2009 12:24 am
by Roboto
I have seen the post in the past. That is crazy amazing and way, WAY outside the scope of this project.

Ignore my newb interpretation, but a small pipe+sprinkler valve to the barrel would allow multiple shots per charge, correct?

That is, if that isn't outside the scope or budget of this project as well.

Re: Double PC WBL

Posted: Thu Apr 30, 2009 1:13 am
by Silence
Using a narrow valve or one that's open for too little time will lead to performance. You'll conserve air but only because it isn't being used to propel the balloon.

My suggestion is multiple pressure chambers all leading to the barrel, or in parallel. As others have noted, having them in series would reduce the pressure and range with each shot.

I encourage you to consider using higher pressures and a regulator. Generally such a system uses carbon dioxide (1000 PSI) or "high pressure air" (up to 3000 PSI), filled at a store, but it's viable with a 200 PSI home compressor, too. Regulating down to 50 PSI would quadruple the volume of air. I agree it's a bit more complicated, though; if you're not comfortable adding all those extra valves, then don't do it.

Remember, most people end up setting their sights lower and building a single-shot WBL. ;)