Oxy-fuel torches along with fuel pipelines are used in various metalworking facilities for cutting or welding strong metals. The fuel gas is directed at the metal at a particular pressure. Any change in the pressure may cause the flame to flow towards the tip of the torch or backwards, which may lead to severe damage if not curbed properly. This is where the role of a flashback arrester becomes important. It serves as a safety device in facilities where various types of oxy-fuel torches and fuel pipelines are used for welding and cutting purposes. Before discussing the importance of this device, it is important to know the different types of flame discrepancies that may occur in a facility. This post discusses these discrepancies, and the importance of flashback arresters in detail.
What Are Flashbacks, Backfires, Backflows, and Sustained Backfires?
Acetylene cylinders or oxy-fuel torches used in welding and metal cutting workshops may experience flashbacks, backflows, sustained backfires, or backfires. These terms may sound similar; however, there are slight differences between them. It is important to identify them if they occur in any workshop. The below-given differentiation will help you understand them better.
- Flashback: It is a progression of flame upstream in fuel pipelines or torches. A flashback mainly occurs due to the reverse flow of gases upstream into the equipment or hoses. There are several causes of reverse flow such as ambient cylinder pressures, improper start up or shut down procedures, or using a check valve that is not working properly. It attains a dangerous dimension when the flame progresses to the hose, where it may rupture the hose or separate it from the pipeline. In extreme cases, this flashback may also lead to explosions.
- Backflows: At times, the gases operated at high pressure may flow back into the hose through the torch at a low pressure. This leads to dangerous mixing of gases in the hose, which may lead to damages such as severe explosion or fire.
- Backfire: This occurs when the flame enters into the torch or a nozzle with a violent sound, which may re-ignite or extinguish in the nozzle. Backfire is only a momentary phenomenon, and it may not sustain for a long time. In most cases, the flame is reignited when a manual lighter is used or when there is an ignition source nearby. Backfire is not considered a prime safety concern, and many leading acetylene torch manufacturers are known to induce backfires to check the integrity of acetylene torches and their tips.
- Sustained Backfire: As the name suggests, a sustained backfire is a term used for the flame that enters into the nozzle or torch and continues burning there for a long time with a whistling sound or a sharp, smoky, or pointed flame. When this happens, a user should close all torch valves in the vicinity immediately, otherwise, the flame may cause severe damage to the torch, and even erupt fire. In most cases, sustained backfire can be easily contained within the torch. However, in torches with thin wall conditions, the flame may breach outside, melt the material, and even erupt fire.
How Does a Flashback Arrester Work?
As the name suggests, flashback arresters are designed to prevent the flame from flowing back to the hose and the regulator through the torch. All advanced flashback arresters are equipped with check valves or coiled tubes that help prevent the reverse flow of gases. Today, flashback arresters feature at least three safety components— the flame arrester, the non-return valve, and the thermal cut-off valve. These devices are distinguished into two types— wet flashback arresters and dry flashback arresters.
- Dry flashback arresters use a combination of several elements to quench the flashback or reverse gas flow.
- Wet flashback arresters utilize non-gas absorbing liquids such as water to quench the flame from detonation or deflagration.
These flashback arresters are used in the facilities where oxy fuel gas cutting, welding, heating, as well as other allied processes are conducted. Flashback arresters are used on torch inlets, hoses, and regulators of fuel gas piping systems to avoid flashback. The flame arrester ensures a free flow of gas through the pipeline at a regular temperature. Under abnormal conditions, it may prohibit the flame from traveling between the hose and the regulator. Reverse gas flow is stopped by the spring-loaded non-return valve, which prevents the mixing of gas in the low-pressure chamber.
Nowadays, these flashback arresters are equipped with hollow cylindrical filters to stop a flashback, and also protects against dirt. The flames are made to pass through the filter, where they lose their energy. In this way, the flashback is extinguished in a fraction of a second. These flashback arresters can be mounted in any orientation and are available in various materials of construction. If you are buying them for your welding or cutting facility, it is important that you source them from a reliable manufacturer like Rexarc. The company provides flashback arresters in various configurations and customized designs to suit your requirements.