In the process of gas welding or gas cutting, sometimes the reverse combustion of gas flame into the nozzle occurs, which is called tempering. When tempering, once the flame of reverse combustion enters the acetylene generator or acetylene bottle, a combustion explosion accident will occur. The function of the backfire preventer is to prevent the flame from flowing into the acetylene generator or acetylene cylinder or from burning in the acetylene pipeline when the welding torch or cutting torch backfires, thus ensuring the safety of the acetylene generator or acetylene cylinder. Therefore, acetylene generator or acetylene cylinder must be equipped with flashback preventer.

When the welding nozzle of welding torch or cutting torch is blocked, the overheating of welding nozzle or cutting nozzle will increase the gas pressure and increase the flow resistance of mixed gas, the working pressure of acetylene gas is too low or the rubber tube is blocked, the welding torch and cutting torch are in disrepair, etc., which will reduce the outflow speed of mixed gas, the flame burning speed is greater than the outflow speed of mixed gas, and the backflow of oxygen can lead to tempering.

According to its working principle, tempering preventer can be divided into two types: water seal type and dry type. According to acetylene pressure, it can be divided into low pressure type (less than 0.01MPa) and medium pressure type (0.01~0.05MPa). At present, there are two kinds of dry tempering preventers commonly used in China, namely, medium pressure explosion-proof membrane type and medium pressure metallurgical type. The backfire preventer must be used in strict accordance with the following requirements:

1) The flow rate and pressure of the flashback preventer installed on the acetylene generator must be compatible with the gas output and acetylene pressure of the acetylene generator.

2) Use medium-pressure metallurgical sheet dry tempering preventer or medium-pressure porous ceramic tempering preventer, which requires acetylene to contain less impurities and moisture, and acetylene station should install dryer and purifier. In use, when it is found that the acetylene flow decreases and the resistance increases, the powder metallurgy sheet or porous ceramics should be cleaned.