Assessing the start type-Blow Back
A more modern approach to starting an arc is the use of "blow back" technology. This technology uses a dead short where a spring loaded electrode is firmly seated against the nozzle face and air pressure is applied to the torch. The air pressure pushes the electrode back so the air can escape from the nozzle hole. Simultaneously, electricity begins to flow creating a spark between the nozzle which is grounded back through the machine to complete the circuit, and the electrode. This ionizes the air, and a low amperage plasma arc is established. This design automatically includes a pilot arc. It cannot work unless there is a complete circuite within the torch head. This start type poses no threat to surrounding electronics, or to the machine itself. It can be a little slower start than the HF style, but most people see little or no difference. Some disadvantage exists in the fact that occasionally the arc won’t start, but usually only in very rare cases. Most major companies utilize this style start under 100 amps. The inherent design creates problems for use in plasma cutters greater than 100 amps, however. An advantage of this design is that there are no high frequency points to maintain, and the start style is very friendly and can be used in sensitive areas. Most people after using both blow back and High Frequency start styles, find little practical difference in regular cutting. However, regardless of the start style, the pilot arc is usually the thing that most people feel they cannot live without. A blowback torch consists of moving parts, but usually, life span is nearly that of a High Frequency torch. But it is usually considerably more expensive for the blowback torch than a High Frequency torch, should one need to be replaced. The Blowback style does typically have more parts, and is more sensitive to any small variation in improperly set parameters, especially air pressure.