Pneumatic Air Cannon

Flameless not equal to funless

Wichita Falls city and county authorities have made clear that fireworks will not be tolerated this July Fourth. Even their sale, for the time being, is illegal.

Independence Day, however, calls for special celebration. Most families admit half the fun of the Fourth comes from hearing the familiar pop of fireworks or watching bottle rockets explode in midair.

Fans of the sciences, especially younger ones on the nerdy side, know there's more to bottle rockets than what's sold in stands on the county line.

The Internet is alive with safe, do-it-yourself projects that can produce rockets made from water bottles and fueled by nothing more dangerous than a bicycle pump.

Water balloon launchers, potato cannons powered by a shop compressor, soda geysers and rockets that can be fired more than 100 feet in the air with water and compressed air are projects anyone with a little enterprise and very little money can put together.

"We encourage families to try something safe because over the holiday weekend police, the sheriff's department and municipal officers will be out enforcing zero tolerance for fireworks," said Assistant Fire Chief Bill Weske, who mentioned more than 230 Texas counties are under burn bans that include fireworks.

"They should also remember that along with law enforcement, their neighbors will be watching and listening, and will be quick to call us," said Weske.

Many safe ideas can be researched at the public library, but TRN staffers combed the Internet for sites that not only offered thorough project instructions for launchers, water rockets or soda and vinegar rockets, but did so with an eye to safety.

Some of their favorites included:

■ Wired Science, a PBS program, has a great website, www.pbs.org/kect/wiredscience / that includes its "Geek Dad" feature. Dads and kids enjoy a variety of experiments but the instructions on how to build a water rocket are most complete. Participants can construct a reusable launchpad for a 4-liter (two 2-liter bottles glued together) water rocket powered by pressurized air from a regular bicycle pump. It might take a half day to put everything together, but the blastoff is worth it. The TRN team is convinced a Roman candle effect could be achieved by adding glow sticks to the bottle.

■ We fell in love with two little boys from Australia who engineered their vinegar and "bi-carb" soda rocket from water bottles and a launchpad from a food storage tub and a disposable plastic tumbler. Their blooper reel is just as funny. Check http://youtu.be/RqtEJP4-olE .

The Double-barrel Pneumatic Air Cannon | JCOPRO.NET

 Is that one side of the cannon holds the pressure (marked in red squiggly lines below) while the other side holds your projectile, water in this case (marked in blue squiggly lines).  Separating the pressure and projectile side is some sort of pneumatic valve – in this case a sprinkler valve.  I’ve put a yellow (golden?) square around these two valves.

Yes, two valves.  Generally most pneumatic air cannons would only have one as they only have one shot per air charge.  This design has two separate air and projectile chambers.  Basically it’s two guns attached together.  To aid in filling each chamber with air, a manifold was created with a PVC elbow and Tee.  Air goes into a Schraeder valve shown by the leftmost red arrow and is split into two by this assembly. The charging air flow is illustrated by the two other red arrows.

In order to avoid discharging both sides at once, the two parallel flows go through a one-way valve.  This way, during charging both pressures will be roughly equal, but after firing one chamber can be close to 0 PSI (gauge pressure for those that know about that) while the other will be charged to whatever it was pumped up to.  The other end can then be discharged at will.

Which brings up the next question, how does one actually get these valves to fire?  In normal operation, the valves used are powered by 24VDC, so if you happen to have a 24 volt battery laying around, that’s one option.  The way this one is done is that three 9 volt batteries are chained together in series giving a combined voltage of 27 volts.  A little more than recommended, but it seems to work well.  Both solenoids were hooked up to individual normally open pushbuttons on the positive side.  The other side was hooked up to negative as shown in the drawing below:

Here’s how this looked in reality:

I used some DIN rail, terminal blocks, and grounding blocks to make a bank of positive and common out of the batteries.  You can find this stuff at Automationdirect.com .  I would definitely recommend using an additional safety switch with this assembly.  Additionally, always keep the barrel pointed in a safe direction.  Even after firing, there can be some air pressure still in the chamber.  If there is a misfire, the valve can be manually triggered by twisting the solenoid.  Definitely useful in some situations.

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