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Re: End-of-tank-dump comment

I use low-cost regulators and metering valves. I usually set the low
pressure side to about 20 psi, and then adjust the metering valve to get the
bubble rate that I want. As the CO2 cylinder runs dry, the low side pressure
will rise to about 30 psi. The bubble rate will increase somewhat
proportionally, but there can never be a dump because the metering valve is
still the gateway that controls the volume of gas that can get to the
aquarium. There is no safety blow-off or any other event. The cylinder justs
runs dry, and then I get it refilled.

Without a backflow valve, there is a very real possibility of water coming
back into the CO2 cylinder once it is empty. Most bubble counters have a
backflow valve built into them, so you might have one and not know it. I've
added a second one so I can open the bubble counter and not get wet when
capillary action sucks water out of the aquarium. The cheap plastic airline
valves with the rubber flap thingy inside work fine, just be sure to point
them the right way.