A flashback arrestor or flame arrestor is a device most commonly used in oxy-fuel welding and cutting

Oxy-fuel welding and cutting

Oxy-fuel welding and oxy-fuel cutting are processes that use fuel gases and oxygen to weld and cut metals, respectively. French engineers Edmond Fouché and Charles Picard became the first to develop oxygen-acetylene welding in 1903...

 to stop the flame

Flame

A flame is the visible , gaseous part of a fire. It is caused by a highly exothermic reaction taking place in a thin zone...

 from burning back up into the equipment and causing damage or explosions. The two main types are dry and wet. Each has its own advantages and disadvantages. Most oxy-fuel flashback arrestors are the dry type.

Dry type

Dry flashback arrestors typically use a combination of methods to stop flashback. This is the type that is typically found on most workshops, home or portable oxy-fuel kits as they work just as effectively with any orientation, need very little maintenance, and are often small and light enough to be installed between the torch and hoses. They include:

• Flame trap to cool the flame front. They are designed to allow free flow of gas through them but to take the heat out of the flame front to get it below the ignition
  Combustion
  Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...
  
   temperature of the burning gas mixture. The most common types are:
  • Sintered metal or ceramic
    Ceramic
    A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
    
    .
  • Layers of mesh.
  • Ceramic beads.
• Temperature
  Temperature
  Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
  
  -triggered valve
  Valve
  A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...
  
  s to stop the gas flow completely. Because it relies on extracting heat from the flashback to stop it continuing, most arrestors have a temperature-controlled valve that will cut off the gas flow when the unit reaches around 90°C, until either the unit cools (if the unit is automatic) or the reset button is pressed (if the unit is manual).
• A check valve
  Check valve
  A check valve, clack valve, non-return valve or one-way valve is a mechanical device, a valve, which normally allows fluid to flow through it in only one direction....
  
   that closes due to the back pressure
  Back pressure
  Back pressure refers to the resistance to a moving fluid by obstructions or tight bends in the confinement vessel along which it is moving, such as piping or air vents, against its direction of flow....
  
  .

Wet type

Liquid seal flame arrestors are liquid barriers following the principle of a siphon where the liquid stops the entering deflagration and/or detonation and extinguishes the flame, they work by bubbling the gas through a non-flammable and ideally non-gas-absorbing

Gaseous diffusion

Gaseous diffusion is a technology used to produce enriched uranium by forcing gaseous uranium hexafluoride through semi-permeable membranes. This produces a slight separation between the molecules containing uranium-235 and uranium-238 . By use of a large cascade of many stages, high separations...

 liquid, which is typically water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

. They stop the flame by preventing it from reaching the submerged intake.

These devices are normally very effective at stopping flashbacks from reaching the protected side of the system. They have the disadvantages of only working in one orientation and tend to be much larger than dry type arrestors. This makes them mainly only suitable for large or fixed installations and the liquid level needs to be constantly checked.

On smaller units having a pressure release valve to prevent the unit from bursting under a severe flashback, the fluid level should be monitored to keep it always above the intake and not so high that the liquid could splash or overflow into the outlet.

External links

• Flash Back And Flame Arrestor (with diagrams)
• http://www.protego.de/en/products/technical-fundamentals/flame-arresters/index.html