Entrained Air in Return Line When Fountain Is On

[dadijun]

Hello... I have a 14,000 gallon fiberglass in-ground pool... The suction side of the pump has a 3-way valve that directs water from the bottom of the pool, the skimmer, or both... The discharge of the pump has a three way valve that can direct water to the returns, to the fountain water feature, or both... When the discharge 3-way valve is directing water to the returns only, there is no issue... When the discharge valve is directing water to the returns and the fountain, I am getting entrained air in the returns...

I have replaced the o-ring in the pump suction-side union, replaced the gasket in the pump screen access panel, and have rebuilt the multiport valve...

I'd appreciate any ideas on next steps...

Thank you...

[Denniswiseman]

I would suspect the 3 way valve before the pump as the only way of getting air into the returns is by a suction side air leak

[dadijun]

Thank you...