Safety nozzles for autogenous welding equipment - with spring-loaded return valve and flame barrier to stop blow-backs

In normal operation, gas flows down one side of the nozzle into a central cylinder, which houses a spring-loaded valve; after going through the valve, the gas passes through a disc of porous sintered material, which also supports the spring, and then out of the nozzle. If there is a back-fire, causing a shock-wave, the flame is held back by the sintered disc which acts on the spring-loaded valve, keeping it closed, i.e. this is a back-flow barrier valve. The blow-back can then go through the sintered disc past a second spring-loaded valve into a chamber from which it can enter the top of the central cylinder; it then presses on a piston which seals the entry-port to the main valve, thus effectively preventing any after-flow.