I've made a diagram of my pool's equipment, which is vital to understanding my question:
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Take a look at the two green arrows. I have two lines coming in from the pool (bringing water into the pump), and there is a valve at the top which allows me to close either one, or use both.
I'm not sure exactly where the left one sucks water from the pool. Presumably the skimmer.
But I just discovered that if I open the right side one, one of the jets/nozzles in my pool's wall sucks water too. It looks like a usual small nozzle. But here's the safety issue: I put my hand in front of it, and I experienced a LOT of instant suction -- so much that it actually hurt my hand, as my hand was drawn towards its suction.
This concerns me greatly, since I've got kids swimming in the pool. If a kid puts their hand on that, it could be strong enough to injure them.
Is it safe for me to set the valve so that that line is fully closed? Should I leave it slightly open so that there's a bit of water flow? Is there any downside to that?
I don't fully understand the physics and construction of it all, so please advise me like a complete newbie.
Secondary question: at the bottom of the deep end of the pool is that circular thing (don't know what the name is). Is it possible/likely that the right line is also sucking from there? Or the left one? How would I know? (I'm sure you understand my concern of diving down to the deep end and getting too close to a strong vacuum.)