Fluid Dynamics Help

[LadyTang2]

1. Is it true that ideally the pipe from the overflow to sump is larger than the pipe from the sump back to tank? Why?

2. Couldn't you just turn down the return pump and use the same diameter piping?

3. Do you want the flow into and out of the sump to be the same? If it's not the same wouldn't the sump eventually overflow or empty if those rates stayed the same? Or is a new equilibrium water level established when those change? How does that work?

 

[BeejReef]

Most of the pumps we tend to put in our sumps are designed for a 1" or less output.

Yeah, typically the drains will be a larger diameter... usually just a margin for error. If you're interested, you can google siphon rates for varied diameters of pipes and tubing. Once you account for reduced flow from the pump due to head pressure (having to pump straight uphill), usually a full siphon of the same diameter would be sufficient to drain it. A larger diameter drain all but ensures that (and helps prevent easy clogs by snails or algae).

It's capacity really. Only as much water can "overflow" and be drained as the return pump can push up and into the tank. That's how the system equalizes, not so much through the diameter of the pipes. The danger is that your pump is too strong for the siphoning capacity of your drain(s). Very rare. Made all the more rarer by the general use of wider diameter drains than returns ;Joyful

You could undersize your drains and throtte back your return pump, but if that valve ever got bumped, you would overflow your display tank. Likewise with a dc controllable pump. Board could burn out or you could screw up programming it.

Almost everyone will, instead, put a gate valve on their primary overflow drain and tune it to accept 98% of the pump's output and allow the remaining 2% to go down the emergency drain(s). This avoids the noisy gurgling, sloshing, toilet-flushing sound of an open siphon.