I recently added a new rainwater tank on my property, and Ms Podicle and I are having serious disagreements about the fluid dynamics through said tanks. It hasn’t been an issue up to now due to the notable absence of anything resembling rain in South-East Queensland for much of the year until this week. I’ve had surprising difficulty finding a satisfactory answer on the net.
This is the setup: We have three tanks, A, B and C that are of equal size but at different heights, with A above B above C. We have a top tank A that collects water from the roof which then flows through a bottom outlet into the top of a significantly lower tank B until a float valve shuts off the inlet when tank B is full. The top of B is well below the bottom of A.
A, B and C are the same volume and size (22,000 litres, if anyone is interested) and all have overflows on their tops.
Tank B has an outlet halfway up (bottom half required for fire water) that is at the same height as the top of the lower tank C. This outlet flows into an inlet a couple of feet above the bottom of tank C (about a fifth of the tank height). There is no float valve on this inlet.
The question is, if you keep filling tank A, what happens? Does water pour out the top of tank C, or does it fill B and C, cause the float valve to shut off and thus cause a flow out the top of tank A?
Calculators allowed, marks given for working.
I will note that the new tank (B) and all connections were installed by tank professionals who presumably knew what they were doing.