What is this valve (Red arrow) on my return line?

[Desmond.TFP]

The Red arrow valve looks different from my other diverters & check valves. Is it some kind of master throttle for the main return? When might it be useful to touch this valve?

My equipment is several feet above my pool, which (I assume) is why I have those check valves.

 

[ajw22]

The pipe with the check valve and diverter is likely your spa makeup line that feeds the spa water when in POOL mode. The valve lets you adjust the amount of water flowing through the spa and spillover into the pool.

The plumber used a 2-way diverter from Pentair for that valve while your others are Jandy. They are functionally identical.

The check valves are there to prevent the spa draining into the pool through those pipes when the pump is off.

 

[Desmond.TFP]

Thank you, @ajw22

I just replaced the check valve flapper above the Pentair diverter. Equipment was off, but while removing the old one the O-ring got sucked up into the plumbing (spa-pool flow, perhaps?). No idea where it went, but all seems to run fine. Have I likely caused a problem?

 

[1poolman1]

Thank you, @ajw22

I just replaced the check valve flapper above the Pentair diverter. Equipment was off, but while removing the old one the O-ring got sucked up into the plumbing (spa-pool flow, perhaps?). No idea where it went, but all seems to run fine. Have I likely caused a problem?

It will, most likely, end up in the pool, spa, or one of the return ports if there is a diverter "eyeball" installed. Biggest issue is it could clog a spa jet. You would have to remove the orifice to get it out. It could get sucked into the booster pump if it went that way. Just watch for it or different noises from the booster pump.