Index

This page is under construction, but should provide an alphabetical list of common spudding terms, as well as a note/definition about the term.

If you feel like it, start adding things.

A

ABS (Acrylonitrile Butadiene Styrene) - A plastic used in plumbing applications. More resistant to shock, low temperature, and chemicals, but difficult to find rated for pressure. Pressure rated ABS is legal for compressed gas applications.

B

Ballistics - The science of the motion of projectiles. Sometime divided into two sub-classes; "Internal Ballistics" is the motion of the projectile while it is still in the barrel, "External Ballistics" is the motion of the projectile after it has left the barrel.

Barrel - Present on all cannons. A barrel is a tube designed to allow the projectile to reach maximum velocity before the pressurized gas propelling it escapes to the atmosphere. Barrels also improve accuracy, and can be rifled to improve accuracy further.

BBMG - See BB machine gun.

BB Machine Gun - Pneumatic gun designed to fire airsoft pellets or metal BBs at high rates of fire.

Bottled Gas - See Gas bottle

Butane - A common fuel for combustion spud guns. Butane, a gas at room termperature and pressure, is readily available in disposable lighters.

C

Chamber - An element shared by all pressure based cannons, where either the pre-compressed air or flammable gas mixture is stored before firing.

Chronometer - 1. A device for measuring time. 2. A device for measuring the muzzle velocity of a gun. See also Chrony, muzzle velocity.

Chrony - A commercial device for measuring the muzzle velocity of a gun. Used for "real" guns, paintball guns, bows, and spud guns.

Combustion Cannon - A cannon that generates pressure by burning flammable gases.

Compressor - Motorized air pump.

Copper - Metal. Construction material.

D

DDT - Deflagration to Detonation Transistion. This very dangerous effect occurs when the flame front in a combustible gas mix exceeds the speed of sound in the gas - creating a super sonic shockwave and a very large pressure spike which may damage or destroy the chamber. It is very rare, and is only likely to occur in high mix Hybrid cannons, or in combustion cannons with very long chambers.

Diaphragm valve - Related to Piston valve. Generally rarer, but often considered to open faster but have lower flow. Typically used in coaxial designs, and commercially manufactured as inline sprinkler valves.

Drain Waste Vent (DWV) - A designation by the NSF (National Sanitation Foundation) that means the item is approved for drain, waste, or venting applications. By nature, DWV does not require a pressure rating, but some DWV pipes are rated for pressure.

E

Epoxy - A combination of chemicals that form a bond much stronger than any glue. Often used for sealing leaks or during sprinkler valve modification. Some people have created very large parts of cannons from epoxy, as well as pistons.

F

Flame Front - The edge of a flame whose speed, in part, affects the power of the cannon it is powering. If the flame front exceeds the speed of sound, DDT occurs.

G

Gas Bottle - A metal cylinder filled with pressurized gases.

H

Hybrid Cannon - A cannon that uses a pre-compressed flammable gas mixture. The increased fuel + oxygen charge in the chamber substantially increases the pressure, temperature and energy in the chamber. Ignition is somewhat difficult, as spark length is roughly inversely proportional to pressure. Very powerful, but requires experience to successfully and safely implement.

I

Ignition source - Used to start the combustion reaction in a combustion cannon or Hybrid Cannon. Sources range from lantern sparkers, to piezoelectric grill ignitors, to ignition coils and camera flash circuits.

L

Lathe -

M

Mach - The speed of sound for a given set of environmental conditions. The speed of sound changes with temperature and the nature of the fluid involved. For dry air at 15C, one Mach is equivalent to 340.3 m/s (1225 km/h, 761.2 mph, 1116 fps). At normal temperatures the small temperature dependence is usually ignored. At the elevated temperatures that exist in the chamber of a combustion gun, the speed of sound is significantly increased. At the adiabatic flame temperature of propane in air the speed of sound is increased by about 3-fold to ~990 m/s (3560 km/h, 2210 mph, 3250 fps).

MAPP - A bottled gas used in combustion or hybrid applications. MAPP has been experimentally determined to produce muzzle velocities 11% greater than those of propane.

Muzzle Knife - (Aka spud cutter.) The sharpening of the muzzle of a barrel so that it will automatically cut a spud to the proper size for the barrel. Internal beveling of the muzzle can produce a better seal. See also spud cutter.

N

Nitrogen - An inert gas with a lower molar mass than the average of air. This allows slightly higher particle speeds, and therefore, higher muzzle velocities.

NSF - National Sanitation Foundation. "NSF" is often printed on pipe, along with letters that designate what applications the pipe is NSF-approved for.

O

O-Ring - Often made of Neoprene or similar, these rings can seal thousands of pounds of pressure, but must be mounted very precisely for most applications, which often requires use of a lathe.

P

Piezoelectricity - A property of certain materials where the material can be mechanically stressed, and produce high voltage electric current. When electricity is applied to the crystal, it vibrates. This property is implemented in grill ignitors, which are commonly used as ignition sources in spud guns.

Pilot Valve - A valve whose purpose is to exhaust pilot air, thus triggering a larger main valve, or, in cases, another pilot valve.

Piston valve - A high power home-made valve which is generally considered to be second only to Burst disk valves in performance, but more practical to use. Releases air by rapidly exhausting the area behind the piston (pilot), thus causing the piston to be pushed backwards, and stop sealing the chamber from the barrel. See also: Diaphragm valve

Pneumatic Cannon - A cannon that uses pre-compressed air for power.

Potable Water (PW) - An NSF designation found on some plumbing pipe and fittings. Potable Water systems are pressurized, so, by nature, NSF-PW pipes are pressure rated.

Propane - A common fuel for combustion spud guns, as well as hybrid cannons.

PVC - Most common spudgun construction material. Gets brittle in cold weather, and may shatter if dropped or abused. Pressure rated PVC is easy to find in the U.S., although large diameter pipe is difficult to find. PVC is illegal for compressed gas applications.

Q

QEV - Quick Exhaust Valve. Essentially a pre-made piston or diaphragm valve. These are quite hard to find, and are moderately expensive.

S

Safety - More important than even the spudgun. If you don't have this, then you need it fast.

Schelkin Spiral - A method that causes turbulence in burning gasses. This increases the risk of DDT.

Spark Gap - A spark gap consists of two metal electrodes placed close to each other with a gap in between, where an electrical spark can jump. They are used for igniting the fuel in combustion and hybrid cannons. Electrodes that are more pointed can generate a longer spark at a given voltage than those that are more planar.

T

Tee - A name for pipe fittings that have sockets arranged so that the fitting looks like the letter "T".

V

Valve - Essential to pneumatic cannons. A valve retains pressure and then opens, or in the case of a burst disk, ruptures, to release the air. A valve will perform better if its flow rate is increased, or its opening speed is decreased.

Vortex cap - Typically a cap in shape and is made out of strong materials such as PVC or metal. Their construction is similar to the Vortex Block, in which an air inlet and a hole for a barrel are drilled perpendicular to each other. The vortex cap was designed by Davidvaini and provides a small substitute to the standard vortex or inline vortex blocks.

W

Wye - A name for pipe fittings that have sockets arranged so that the fitting looks like the letter "Y".