Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
There is a self-starting auto-siphon method of setting up the plumbing so that it is supposed to re-start itself if the power goes out. It is not very reliable.
Here are the thoughts:
1) When everything is working right the outflow = inflow. The pipes that carry the water out (gravity/siphon) must equal the flow from the pump. If the outflow pipes are capable of carrying more, that is good. I have my larger tanks plumbed with 1" PVC (schedule 40) out and 3/4" pumped returns.
When a problem happens...
2) Electricity out or pump stops for some other reason.
Have a flapper style one way in the line so the water from the tank cannot back up through the pump. Keeping the pipes from the pump way high up in the tank is good, too, for example the water returns to the tank via a spray bar that is right up at the top. Then, a little water drains down, and the possible overflow from this route is cut off. Those flappers can get blocked with debris, so clean it often. Put a union in the pipe so you can take it apart.
Now the electricity comes back on. How does the water get flowing again? From sump it is pumped into the tank, but to get out of the tank the siphon MUST auto-start. (Guaranteed: You won't be home when this happens!)
3) Debris clogs the siphon, so that reduced flow leaves the tank. The pump is still pumping full flow. Tank can overflow, sump run dry, pump burn out.
You MUST design to avoid this. Grid over the intake, multiple intakes, You clean it every few days...
4) Sump runs dry. (opps you forgot to top it off, or the siphon stops removing water from the tank). Get a float switch that turns the pump off. (now see item 2- pump has stopped)
Google any and all terms you can think of that could mean self starting siphon.
Basically the water enters the pipe in the tank, then follows a convoluted path to the sump. If the flow stops, there is water trapped in the pipe and this re-starts the siphon when the pump starts filling the tank again.