A check valve is a spring-loaded valve that allows flow in one direction but prevents flow in the reverse direction. It is used to reduce the possibility of forming an explosive mixture of oxygen and fuel gas in the hose in case one or the other gas backs up in the system. They are normally mounted at the torch inlet connections, but models exist for installation at regulator outlets as well. Check valves must be tested frequently to make sure they are not leaking in the reverse direction due to dirt accumulation on the valve seat. It must be understood, however, that a check valve will not stop a flashback in the system if a mixture of oxygen and fuel gas is somehow present and ignites. The flashback flame will pass right through a check valve.
A flashback arrestor is a safety device that incorporates a porous metal filter (or other means) to stop the flashback flame and prevent it from traveling farther upstream in the system. Most flashback arrestors also have a built-in reverse flow check valve to help prevent a gas mixture from forming in the first place. Various models of flashback arrestor are available that perform other functions as well. Some incorporate a pressure relief valve to protect equipment from the pressure wave from a flashback, and others include a thermal cut-off to stop the flow of gas if the flashback arrestor overheats due to a fire. Models are available for mounting at torch inlets or regulator outlets.
If the check valves are properly tested regularly they are probably about as safe as flashback arrestors.
answered 1 year, 8 months ago
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