How to prevent glass laser tube internal crack?

Many people turn on the water chiller and start the laser machine without checking the laser tube every time. It is fine most of the time. However, trapped air bubble can be the killer of the laser tube. Please do not assume there is no air bubble introduced if the machine worked fine yesterday. Bacteria and fungi can generate air bubble. Old connection/leaking can let air get in too. Replace water tube when it is old. If there is trapped air, try to squeeze the water tube a few times to move the bubble. Disconnecting the water tube to drain out a little water also works. If the water line is long, even a high power pump can have low flow rate, which may be too weak to move bubbles. The glass around air bubble can get hot, but the water around it is cool. That temperature difference causes the crack. Glass also cracks when there is a rapid temperature change, so do not suddenly pour in cold water when the glass is warm, or pour in warm water when the glass is cold. Next time before using the laser, please spend one minute to hunt down the bubble. It could save you money and avoid downtime.