Harris 543MX Acetylene FAQs
Acetylene cutting, welding and gouging parts for a medium-duty gas torch, with practical advice on choosing and using them.
What does a cutting attachment do compared with the handle it fits?
The handle, or shank, carries the gas from the hoses and holds the valves. A cutting attachment fits onto it and adds the extra oxygen route that cutting needs. A cutting nozzle uses oxygen in two ways: some is mixed with the fuel gas to feed the preheat flames, and a separate lever-controlled supply gives the cutting jet.
The preheat flame brings the steel up to temperature, and the cutting oxygen then burns through it. Check that the attachment, mixer and nozzle you choose are specified for your handle and for acetylene.
What working pressure should I use for acetylene?
Acetylene is used at low pressure on the torch side, much lower than the cylinder pressure. HSE guidance says the acetylene pressure should not exceed a low limit for most welding and cutting unless the equipment has been specifically designed for more, so do not raise it to compensate for a worn or blocked nozzle.
Set the pressures for your nozzle size from the manufacturer's data. Use only regulators, hoses and blowpipes designed and marked for acetylene and oxygen, and read the data plate and manual for anything specific to your equipment.
Why does the nozzle size affect how much acetylene I can draw from one cylinder?
Acetylene is dissolved in acetone inside the cylinder. If gas is drawn off too quickly, acetone can be carried into the gas, which may make the equipment malfunction, and acetylene can also condense and drip from the torch, which is a fire risk. The rate of withdrawal should therefore be restricted to the values given in the BCGA guidance.
Large nozzles and heating heads use a lot of gas, so check the maker's flow figures against your cylinder size. Your gas supplier can advise whether you need more than one cylinder connected, which has its own rules.
Which flame should I set with a welding nozzle?
Gas welding of steel is normally done with a neutral flame, which has equal quantities of oxygen and acetylene. Adding more oxygen gives an oxidising flame and adding more acetylene gives a carburising flame, and these are used only for particular jobs.
Welding nozzles are made in a range of sizes selected by the thickness of metal and the welding speed required, so choose the size from the maker's chart. A swan-neck copper nozzle is fitted to the blowpipe, and the right size is the one that melts the joint without overheating the work.