A potato launcher is a DIY air cannon that fires a potato (or similar projectile) using either compressed air or combustion. Both designs use PVC pipe, a few hardware store fittings, and basic tools. The compressed air version offers more consistent power and is easier to control, while the combustion version is simpler and cheaper to build. Here’s how each one works and what you need to put one together.
Combustion vs. Pneumatic: Pick Your Design
The two main types of potato launchers work on fundamentally different principles, and your choice affects every other decision in the build.
A combustion launcher has a large sealed chamber where you spray in a flammable fuel, then ignite it with a spark. The rapidly expanding gases push the potato out the barrel. These are the classic “spud guns” you see in backyards. They’re less expensive, require fewer specialized parts, and can be assembled in an afternoon. The tradeoff is inconsistent power: every shot depends on how much fuel you spray in and how well it mixes with air before ignition.
A pneumatic launcher uses a pressurized air chamber and a fast-release valve. You pump the chamber to a set pressure with a standard air compressor, then trigger the valve to release all that air at once behind the potato. Pneumatic builds are more complex and cost more, but they deliver repeatable performance and let you dial in exactly how much force each shot carries by adjusting the pressure.
Materials You’ll Need
Both designs share a common materials list for the body, with differences in the firing mechanism.
The Body (Both Types)
- Barrel: 2-inch Schedule 40 PVC pipe, roughly 3 to 4 feet long. This is the tube the potato travels through.
- Chamber: 4-inch Schedule 40 PVC pipe, roughly 12 to 18 inches long. This holds the compressed air or combustion gases.
- Reducer coupling: A 4-inch to 2-inch PVC reducer connects the chamber to the barrel.
- End cap: A 4-inch PVC end cap seals the back of the chamber.
- PVC primer and solvent cement: These chemically weld the joints together. Do not substitute regular glue.
- Teflon tape: For sealing any threaded connections.
Combustion Firing Mechanism
- Grill igniter: A piezoelectric push-button igniter (the kind from a gas grill) mounted through the chamber wall.
- Threaded cleanout adapter: A 4-inch threaded adapter and plug on the back of the chamber, so you can open it to spray in fuel and ventilate between shots.
- Fuel: Aerosol hairspray is the most common choice for casual builds. Butane produces average muzzle velocities around 35 m/s (roughly 78 mph). Methanol performs better at about 48 m/s. Propane is actually the weakest performer at around 28 m/s. Hairspray varies widely depending on the brand and propellant blend, which is part of why combustion launchers are inconsistent.
Pneumatic Firing Mechanism
- Sprinkler valve: A 1-inch Orbit irrigation sprinkler valve, which will be modified to open quickly.
- Compressor fitting: A 1/2-inch male-to-male compressor fitting.
- Blow gun: A standard air compressor blow gun with a 1/2-inch opening. This becomes your trigger.
- Schrader valve: A tire-fill valve mounted in the chamber so you can pump it up with a compressor.
- Epoxy: For sealing internal ports on the sprinkler valve during modification.
A Critical Note on PVC Selection
This is the single most important safety decision in the entire build. Use only Schedule 40 or Schedule 80 PVC pressure pipe. Never use DWV (Drain, Waste, Vent) pipe, which looks almost identical but has thinner walls and is not pressure-tested by the manufacturer. DWV pipe is designed for gravity-fed drainage systems and can shatter violently under pressure.
Schedule 40 PVC in 2-inch diameter is rated to 280 psi. In 4-inch diameter, it’s rated to 220 psi. Schedule 80 is thicker and rated higher (400 psi for 2-inch, 320 psi for 4-inch). For most potato launchers operating under 80 psi, Schedule 40 is sufficient, but you should never pressurize anywhere near the pipe’s maximum rating. Keep your operating pressure well below half the rated limit.
Also avoid any PVC that’s been sitting in the sun for extended periods. UV exposure weakens PVC over time, making it brittle and prone to cracking under stress.
Building a Combustion Launcher
Start by dry-fitting all your PVC pieces to make sure everything lines up. Cut your barrel and chamber pipes to length with a hacksaw or PVC cutter, and deburr the edges with sandpaper.
Apply PVC primer to both the outside of the pipe and the inside of each fitting, then apply solvent cement to both surfaces and push them together with a quarter-turn twist. This creates a chemical bond that’s stronger than the pipe itself. Cement the barrel into the smaller end of the reducer coupling. Cement the chamber pipe into the larger end. On the back of the chamber, cement the threaded cleanout adapter, and screw in the threaded plug (use Teflon tape on the threads).
For the igniter, drill a hole through the chamber wall sized for your grill igniter’s electrode. Push the igniter through and seal around it with silicone or epoxy. The spark gap should be visible inside the chamber.
Let all cemented joints cure fully before use. For 4-inch pipe at pressures above 180 psi, the recommended cure time is 12 hours. Combustion launchers generate lower pressures (butane peaks around 23 psi internally), so a minimum cure of 2 hours at room temperature is reasonable for the 4-inch joints, though overnight is safer.
Building a Pneumatic Launcher
The body assembly is the same as the combustion version: barrel cemented into a reducer cemented into the chamber. The back of the chamber gets a cemented end cap instead of a threaded cleanout, plus a drilled and sealed Schrader valve so you can fill it with a compressor.
The key difference is the sprinkler valve modification that sits between the chamber and barrel. This valve needs to open as fast as possible to dump all the stored air at once. To modify a 1-inch Orbit sprinkler valve, unscrew and discard the electrical solenoid from the top. Remove the eight Phillips screws holding the top cap to the valve body and carefully lift it off, noting the position of the diaphragm and its spring.
Inside, you’ll find small bleed holes that normally allow water pressure to slowly equalize across the diaphragm. These holes need to be sealed with epoxy so that air can only escape when you trigger the blow gun. Apply epoxy to each hole and let it cure for a full 24 hours. Then reassemble the valve with the diaphragm and spring in their original positions, making sure no debris has gotten inside.
Thread the 1/2-inch male-to-male compressor fitting into the port where the solenoid used to sit, using Teflon tape. Screw the blow gun onto the other end of that fitting, again with Teflon tape. Don’t overtighten the fitting into the valve body, as forcing it can crack the housing or prevent the diaphragm from seating properly.
When you pull the blow gun trigger, it vents the air above the diaphragm. The higher pressure below instantly pushes the diaphragm open, releasing the full contents of the chamber in a fraction of a second.
Preparing the Barrel and Loading
A potato launcher only works well if the potato forms an airtight seal inside the barrel. The easiest way to achieve this is to sharpen the outside edge of the barrel’s muzzle end into a beveled chamfer, essentially turning the barrel into a cookie cutter. Use a file, knife, or sandpaper to create a sharp edge angled outward around the circumference.
To load, set a potato on a flat surface and push the muzzle straight down into it. The sharpened edge cores out a perfect cylinder of potato that fits snugly inside the barrel. Use a dowel or broomstick to push it down to the base of the barrel, right above the chamber opening. If the potato slides through too easily, it’s too small and won’t hold pressure. You want a firm, tight fit.
Firm, fresh potatoes work best. Older potatoes that have gone soft won’t hold their shape or seal properly. Apples work well too, and some builders prefer them for the cleaner cut and tighter fit.
Firing and Safety Basics
For a combustion launcher, unscrew the rear plug, give a one-to-two-second spray of hairspray into the chamber, and immediately screw the plug back on. Point the barrel in a safe direction and press the igniter. If it doesn’t fire on the first click, wait a moment and try again. After two or three failed attempts, unscrew the back and ventilate the chamber before re-spraying, as too much fuel actually makes ignition harder by creating an over-rich mixture.
For a pneumatic launcher, fill the chamber to your target pressure using a compressor (40 to 60 psi is a common starting range), point the barrel safely, and squeeze the blow gun trigger. The shot is nearly instant.
A few things that should go without saying but are worth stating plainly: never point a potato launcher at a person, animal, vehicle, or structure. These devices can send a projectile hundreds of feet. Never look down the barrel of a loaded or pressurized launcher. Always fire in an open area with a clear line of sight and a safe backstop. Never exceed the pressure ratings of your materials, and inspect your PVC for cracks or damage before every use. PVC does not fail gracefully: when it ruptures under pressure, it fragments into sharp shards.
Many jurisdictions regulate or outright ban potato launchers, classifying them alongside firearms or destructive devices. Check your local and state laws before building one.