DC excited glass CO2 laser tubes (as well as some high power RF exited metal tubes) are water cooled. The typical coolant is distilled water. This is important because the conductivity of distilled water is much lower and it does not readily promote algae growth. With the K40 laser engraver the cooling system usually consists of a small submersible pump placed in a reservoir with around 5 gallons of water. I typically add 7-12 drops of aquarium algaecide and 7-10 drops of dishwashing liquid to 4.5 gallons. The algaecide for obvious reasons and the dish soap to act as a surfactant which helps flow rate and prevents microbubbles from forming due to surface tension on the walls of the tube. It is also a detergent. I have been running the same water for over a year with no issues.
The ambient room temperature, total water volume, and laser usage all affect the performance of the cooling system. The ideal temperature range is between 10 and 24 degrees C. Higher temperatures will decrease the life and performance of the tube and can cause critical failures. If the tube freezes it is gone. If you have the unit in freezing temperatures you can add a special antifreeze to it. Do NOT use automotive antifreeze/coolant (ethylene glycol) as it is a corrosive agent and oxidizer and it also raises the level of conductivity of the coolant enough to allow arcing of the tube. The correct type of antifreeze is RV Antifreeze (propylene glycol). It is non-toxic and does not affect conductivity enough to cause arcing in most cases. You can find more on Coolants & Additives HERE.
As far as tubing for the laser only use food grade silicone tubing (8mmx12mm is a standard size). Other tubing materials can be electrically conductive and can leech impurities into the water.
It is important to accurately monitor the temperature of the tube. It is also strongly recommended to add a pressure/flow switch to the system if it does not already have one. This will prevent the laser from firing if these is a coolant system failure. There are various types and configurations of these systems and will be discussed in more detail in future articles.
If you experience higher than desired temperatures you can add more coolant volume, reduce ambient temperature, adjust power and duty cycle of the laser engraver, add ice to the coolant, etc… There are also industrial chillers available which will regulate the temperature. Some of the commonly mentioned “chillers” are the Chinese CW-3000 and CW-5000 series. Beware when looking at this option because the 3000 series is not a chiller. It is a passive cooler. It uses and air cooled radiator and a fan. The 5000 series usually has active cooling. This means there is a condenser, evaporator, compressor, etc… in it that can cool well below ambient temps.
When looking at CW series chillers make sure they are real S&A brand units and not a clone. There are also chiller made for aquariums that are active and are a good choice. It is important to to your research before spending all that money on a chiller and make sure it is right for your specific situation. See the documentation on identifying S&A chillers HERE.
The video below outlines my cooling system on Cyclops: