Also what about De-ionised water as opposed to distilled water? de-ionised water is alot easier to find in the UK
@John_Sturgess DI water will be essentially the same as distilled in this case.
All, Lets not miss the critical point here.
Whatever fluid you use for cooling, including whatever additive you use, the aggregate should have conductivity close to distilled water. So the only way to know is to measure what you actually have.
There are lots of conductivity meters choices for sale and I suggest a meter should be in everyone’s laser toolbox and part of monthly maintenance. Conductivity is one of the common measurements for water quality so the meters are pretty inexpensive.
Getting this wrong is just to expensive and you won’t know its wrong until you blow a supply and a tube. Damage manifests itself over a long period of time. So initially if you have the wrong coolant you may not see anything wrong.
There is strong enough evidence that cooling fluids with to high a conductivity blows LPS and damages tubes.
This is what I use but it is pricey:
Here is a cheaper one but I have no experience with it:
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I am adding to my list of research, finding the right range for coolant conductivity.
We know 2.6 uS is a good and 600 uS is bad.
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It would be great if we got a gaggle of measurements from this community of what is in everyones bucket.
To get conductivity as close as possible to distilled water - I use distilled water 
@greg_greene that’s what I should have said. LOL…
At first it was kind of surprising to me that the conductivity of the cooling water has this kind of effect considering the high resistivity of glass. After thinking about it some, I think it speaks to the quality of the glass use in the tubes. At the temperatures we are using, conductivity in glass is mainly due to interstitial migration of Na+ ions. Also it may also be due to a high dielectric polarization of the glass which would be enhanced by cooling water containing lots of ions.
Lol this was making me nervous. https://youtu.be/_t0-KBDyZvQ
@Nedman I don’t know. Do you think this is dielectric breakdown or the lichenburg effect followed by thermal breakdown as the glass was heated?
It looks to me like it was not going through the glass but around it on the surface.
Then again glass’s dielectric strength is 470KV/meter.
Yeah I agree that what is shown in the video is not really dielectric breakdown but increased surface mobility of ions as it’s heated up.
@Nedman I still wonder how there is current flow (an arc) from the plasma to the water. My tank is floating from gnd. Wonder what the path for current is?
Could the current path be from anode to cathode of the laser tube, but through the water instead of the co2?
@TwelveFoot mmm that’s an interesting idea.
I noticed that the current did no fluctuate during the screeching as I expected since I imagined a leak (parallel) might reduce the current to the tube.
In your scenario (serial) a leak would not change the current through the cathode.
So in that case the water is conducting so well that it’s acting as a short circuit?
Only used my laser once for a few minutes, so take this as a grain of salt. With just tap water, it seemed to only/mostly screech when below 8ma.
I hadn’t payed much attention but I’d thought the screeching was coming from the tube.
Don and guys, as is often the case with forum posts, my point did not come across. Forget RV antifreeze conducts too much, my point was as an additive its not going to prevent growth long term. So I ruled it out. From posts(from ignorant people?, not that I know) it sounded like they were getting rampant anode/cathode corrosion.I dont even know if the water contacts them…and could not find a definitive answer. So I opted for an available solution.
Sure as little green apple today, doing some 85% power tests I got what must be the screeching today. So I will be picking up more distilled water in a few minutes and flushing my system. The treated water will be saved until I can test it and or determine the cause of screeching.I’ll report back later on results.
http://answer.So
If we are talking about electrolytic / solution conduction then that would have to involved some kind of chemical redox reaction. Like electrolysis of NaCl (2 NaCl + 2 H2O → 2 NaOH + H2 + Cl2). Has anyone noticed bubbles forming at the anode? It would also be interesting to get pH values of water samples as well.
While I’m a primarily a chemist by trade/education, electrochemistry is not my forte. I will have to dig out my electrochemistry book later to make sure I’m thinking about this right.
Unless the water does not contact metal in the tube, corrosion will occur unless the Chinese are doing something special. Distilled water will still corrode many metals including steel.Apparently ultra pure water is worse and actually bad for human consumption as an aside. Lots of urban myths stuff involved so check lots of sources to research.
@donkjr as the HV expert here, what is actually screeching in the electronics? Just out of curiosity.
@Steven_Whitecoff the problem with Ultrapure water in contact with metal is that it leads to increased metal ion leaching since that is a nonequilibrium condition.
In the general design of these gas tubes, the electrodes should not be in direct contact with the cooling water unless it is poorly made.
Thats great news, visually I could NOT tell. Distilled water and algae control…OK thats the program.
I mentioned the UPW as apparently any advantages come with dangers, not to mention with the materials involved, it would never stay UPW. I wonder if all this is a bit of a goose chase cause by long term exposure to cheap chinese plastic, pump metal and glass. This whole measure it thing seems to be the best way to track down what is going on.
@Steven_Whitecoff It probably is a bit of a goose chase since it seems all you need to do is use clean reasonably pure water. However @donkjr has a penchant for wanting to know why things happen, and I do as well, so I’m just throwing my thoughts into the discussion.