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Water Torches / distilled / deionized water


Regarding the water for water torches, distilled is OK. If the
"distilled" water you happen to be getting is actually de-ionized,
then that’s considerably better. distilled is the less pure of the
two types. The reason is that distilling water only eliminates those
mineral type impurities that don’t evaporate. Anything volatile will
still end up in the distilled water. things such as organic solvents,
alcohols, a host of oils, and other such stuff. Many of these
contaminants wreak havoc on some industrial processes, such as
electroplating baths, so for these uses, de-ionized water is a must.
But a water torch isn’t so picky. It just needs not to get scale and
crusty stuff from dissolved minerals depositing in the torch chamber.
By the way, de-ionized water is available in a range of purity
levels. Very pure deionized water turns out to be an excellent
electrical insulator, while increasing levels of almost any impurity
(ions) lets it conduct more and more current. So DI is often
specified just in terms of it’s electrical resistance levels. The
higher the electrical resistance of the stuff, the purer it is.

Sometimes, the uses to which this is put are surprising. The laser
welder we have where I work uses a high voltage flash lamp (like a
super photo flash) to “pump” the laser rod. Both it, and the laser
rod itself, are absorbing quite a bit of heat, and require effective
cooling in order not to quickly self destruct. The method used is
that the entire chamber in which the laser rod and the flash lamp are
contained is filled with flowing water. Since that flash lamp is
operating at a voltage of as much as 500 volts, and the terminals of
the lamp are part of the bulb and also need cooling, those terminals
too, are simply immersed in the water flow. In order to keep the
whole thing from just shorting out, Deoinized water is used as the
coolant. It’s high resistance value lets that flash lamp be powered
properly, even under that water bath…

but it should also be mentioned that sometimes, purer is not actually
better. Highly pure deionized water is still an agressive solvent.
More so than plain water. DI is actually somewhat corrosive, and in
designing equipment to use or produce it, some care is required as to
the materials used, since DI will quickly become contaminated by
corroding the materials it’s used with if those materials are prone to
that attack. Once it’s absorbed enough impurities to become somewhat
more slightly electrically conductive (like most water already is),
then it’s corrosive nature becomes lessened, but by then, the purity
for which it was chosen is gone…


Peter Rowe