Boomstick_opener

The super-loud Boom Stick is a PVC air cannon that delivers maximum bang for the buck. It assaults the startle reflex of any nearby victim, adding an instant rush of physical terror to haunted houses, art pieces, pranks, and performances.

I work in haunted houses during the Halloween season, as an actor, guide, technician, makeup artist, and effects creator. Some of my effects instill fear through foreshadowing or complex storylines, but the most effective way to scare people is often just a simple, brute-force startle.

The air cannon is a great and safe device for such scares. In its simplest form, it consists of an air reservoir, a quick-exhaust valve (QEV), and sometimes a resonating chamber. Haunted house suppliers and special-effects houses sell commercial models with large-gauge QEVs, but these cost hundreds of dollars. Home projects that rely on a standard air compressor typically use smaller, cheaper water valves from washing machines or sprinklers, but for me, these designs have yielded only a disappointing “poof-hiss.”

Inspired by the PVC-based designs of spud gun enthusiasts (but leaving out the potato), I’ve found a better approach: a two-stage, chamber-sealing, quick-exhaust, piston-valve air cannon that you can build out of common plumbing components for about $100. I call it the Boom Stick.

Building Boom

The Boom Stick creates a pressurized volume of air and releases it very quickly, generating a loud shockwave.

How It Works

Boomstick2

The piston rests in the piston carrier, and the entire system is at ambient air pressure. Small holes in the piston allow limited airflow through from behind; a rubber washer inside the piston acts as a check valve, passing air in only one direction and increasing efficiency.

Boomstick2b

When air flows in behind the piston faster than it leaks out of the holes, pressure builds up in the manifold.

Boomstick3

Pressure behind the piston pushes it into the boom valve tube, sealing the pathway between the air supply and reservoir.

Boomstick4

Pressurized air slowly fills the reservoir through the holes in the piston. The cannon is loaded once the pressures between manifold and reservoir balance.

Boomstick5

To fire the cannon, a small exhaust valve opens and releases air pressure behind the piston, drawing the piston back into the manifold. As soon as the piston clears the boom valve tube, the pressurized contents of the reservoir release into the atmosphere with an impressive bang.

Caution: Dangerous Project

At normal temperatures, standard Schedule 40 PVC has a working pressure of around 150psi, but heat, sunlight, solvents, scratches, and time make the material lose strength, and even at the 40–60psi used for this project, it will eventually fail. When it does, it will break into fragments that will be thrown with great force by the compressed air. Always operate your Boom Stick inside a solidly built plywood box or wall, so that shrapnel cannot reach anyone’s tender flesh.

ABS plastic does not shrapnel like PVC, but the common type used for DWV (drain/waste/vent) applications is not pressure-rated, so it may or may not hold up. Foamcore PVC or ABS is even more lightweight and must be avoided at all costs.

Pressure-rated ABS such as Duraplus from Ipex is the perfect material for this project, but it costs 10 times as much as Schedule 40 PVC. Copper and other metal pipes are similarly expensive.