Plumbing question....is a siphon created when input doesn't equal output?

[Veccster]

On an equipment pad that is higher than the pool body....

If water volume on the supply side exceeds water volume on the return side, will the supply side drain backwards to the pool (more water weight)? I have 2 x 2" pipes on supply side and 1 x 2" pipe on return side.

I'm guessing it wouldn't if the returns are submerged (closed loop would only suck more water into the pipe). But what about water features that return above water (deck jets, water slide)?

I know a check valve would eliminate this so I guess it's more in theory.

 

[gwegan]

A properly sealed suction side won't drain back in. Return sides often drain back depending on how constructed.

 

[Veccster]

How can the return side drain back in without pulling from the suction side? How would air get into the system?

 

[gwegan]

Vacuum release valves in a solar system, open waterfalls or the like. Water generally won't run through the stopped pump or the filter.