Regarding water level in a water table...
First....ensure whether or not your plasma torch was designed for use in underwater cutting applications....as this will help to determine what level you should have your water at, second....what is your most important objective?....cutting down on fumes and smoke, or best possible cut quality?
Generally....if your torch is a non high frequency start unit...and most new (within the last 5 to 7 years) air plasma system do not use high frequency starting, rather they have moving parts in the torch body that create the short circuit spark that ionizes the air and starts the process.....then you should not use the torch submerged. Use these types of torches with the water at least at the bottom of the plate, preferably lower.
With most high frequency start torches there is preflow gas that has the ability to push the water table water out of the torch...and there are no moving parts inside the torch that can be damaged by this nasty water....so you can actaully cut submerged with high frequency start plasm torches...although check with the manufacturer!
Rules of thumb....
1. Cutting underwater virtually eliminates all smoke.
2. Cutting underwater causes striations (roughness...or very pronounced lag lines) on the cut edge. This is partially caused by the production of hydrogen during the cut.....which combusts and then pushes the plasma arc around....and partly by the effect of the water affecting the thermal effects of the arc.
3. Underwater cutting minimizes ultra violet glare...in fact there are water table dyes available that minimize the glare more effectively.
4. Underwater cutting minimizes audible noise.
5. By experimenting with water level....you can usually find a happy medium that minimizes striations and provides an acceptable level of fumes and smoke.
Jim Colt
