Interesting thing happened today.
I had to run a quick engrave on something for my wife, so I booted my Glowforge into the factory firmware so I could use the GFUI.
While running the engrave, I noticed large pockets of air inside the tube. Normally, any bubbles are rare and they are whisked away quickly. Something was clearly amiss.
I opened the unit to find that the water pump was not running. I consoled in and found the pump was set to on. I wiggled the connector on the board, and the pump came back to life and all the air was purged from the tube.
Once upon a time, I recall the firmware testing for coolant flow. It did this by having two temp sensors in the fluid path with a heater between them. By energizing the heater, the firmware could detect that the coolant was cooler upstream from the heater, and warmer downstream.
I’m not sure if this still happens. I’m going to deliberately disconnect the pump one of these days to test…
One thing is for certain, they are definitely not checking for coolant flow while the unit is running a job. This would explain why people have had the dreaded catastrophic tube explosions.
The same would have likely happened to me had I let it run any longer.