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Practical answers on choosing nozzles, lighting up, looking after and safely using nozzle mix cutting torches.
On a nozzle mix torch the fuel gas and the preheat oxygen travel to the head in separate passages and only meet and mix in the nozzle itself. The cutting oxygen has its own passage and comes out of the centre bore. Because the preheat gases are not mixed further back in the torch, the mixing happens right at the flame.This is different from an injector torch, which mixes the preheat gases inside the body, tubes or head and uses the oxygen to draw in the fuel gas. A nozzle mix torch generally relies on the fuel gas being supplied at a proper working pressure rather than being drawn in, so set the regulators to the nozzle maker's guidance.
ANM is the usual designation for nozzles made for acetylene and PNM for nozzles made for propane or other LPG. Both types are made to fit the same style of nozzle mix torch, but you should fit the type that matches your fuel gas, not just whichever one fits the head.The two fuels burn differently and need different internal passages, which is why nozzle designs differ between them. Each torch should be fitted with the nozzle appropriate to the fuel gas in use. Check the markings on the nozzle and the instructions that came with the torch and nozzles before you fit one.
Nozzle size is chosen mainly by the thickness of the steel you will be cutting. The diameter of the cutting oxygen hole is selected according to the material thickness, so thicker plate needs a bigger bore. Nozzle makers publish charts that pair each nozzle size with a range of thicknesses and the oxygen and fuel gas pressures to use.Size numbering is not the same from one maker to another, so use the chart for the nozzles you have rather than a general one. If you are between sizes, the nozzle chart and the torch manual are the place to settle it, and our team can help you choose.
Often yes, provided you fit nozzles made for the fuel gas you are using, and use regulators, hoses and flashback protection that suit that gas. Check that the torch manual lists the fuel gas you plan to use.The two fuels cut differently. Acetylene gives the highest flame temperature of the common fuel gases, so preheating and piercing are usually faster. Propane has a lower flame temperature, which makes piercing slower, but it tolerates a greater distance between the nozzle and the work. Propane also needs more oxygen for combustion than acetylene, and as it is heavier than air, a leak will sink and collect at low levels.
HSE guidance says the blowpipe should be fitted with spring-loaded non-return valves, and that flashback arresters should be fitted to both the oxygen and fuel gas hoses near the regulators. For long lengths of hose, fit arresters at the torch as well as at the regulator.Non-return valves reduce the risk of a flashback but will not stop one once it has started, and an arrester is not a substitute for safe working practice. Check them regularly against the maker's instructions, and after any flashback have the torch, hoses, regulators and arresters carefully checked and replace parts where needed.
A backfire is when the flame burns back into the torch, often with a sharp bang. HSE says it may happen when the torch is held too close to the workpiece or if the nozzle is partly blocked, and it can indicate a fault in the equipment.If one occurs, shut off the torch valves, oxygen first and then the fuel gas, then shut off the cylinder valves. Cool the torch with water if necessary and check the equipment for damage or faults, particularly the nozzle.If the flame burns back into the hose (a flashback), close both cylinder valves only if it is safe to do so. If the fire cannot be put out at once, evacuate and call the fire service. If an acetylene cylinder becomes hot or starts to vibrate, evacuate immediately and call the fire service.