[untamed]

Originally Posted by NateL

Is the pump to maintain siphon? I thought it was just to start it?

No, but man is that ever a common misconception!

Having the pump there certainly makes starting the siphon a lot easier, but it's real value is ensuring that the siphon never breaks.

As the siphon runs, tiny air bubbles get pulled through the siphon and can accumulate at the highest point. If they are allowed to accumulate too much, they can break the siphon.

The pump creates suction on the top of the siphon, removing this bit of air whenever it might happen. For years, I actually ran the pump on the same circuit as my evaporative top off...meaning that the pump would only activate every hour or so. (sort of a random wave maker) You'll see the pump spit out little air bubbles every so often.

Personally, I wouldn't run a siphon of any kind without some sort of similar air removal system.