Old Anti-back-flow valve?

[Gibsonguy]

Hi All,

I just wondered if anyone can confirm or deny my theory. I've never seen any like this, but can this be an old anti-black-flow preventer? The valve turns completely left and right, but it is sealed at the floor. Because the home is 1950 construction and it's in the slab, I am just making an educated guess.. Anyone?

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[Mike Lamb]

Looks like a typical back-flow valve like you surmised.