Originally Posted by Fresh2o
I would say yes. The back pressure will damage the valves and/or diaphragm. These can be replaced of course.
What you should do is get a Tee to join both outputs to a single line and then connect that to a 3 way or gang valve. That way you can open one value to supply air to the tank and another to to handle the excess air.
That is a pretty good idea about the valve. The only reason I don't want to leave it open was that it was more noisy. I put a T in it and connected it, and it blew more bubbles than I would prefer.
I'll try that valve, and hopefully it won't make too much noise.