Is this a backflow check valve?
It looks like it.
Did you bother to get a picture of the label on top of it to check against Google?
This is the only pic I have. A lake on top?
Typo …Tag!
I figured. Is there a chance it is anything else?
Label on top…
By the way, welcome to our forum, Bryan. Enjoy! 
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Right. Could it be anything beside a check valve?
Thanks, Roy!..
It could be a pressure reducing valve. I don’t believe that I’ve seen a check valve with a body like that, but that doesn’t mean it isn’t. A photo of the tag & model number or at least the top of the valve would be useful for the future.
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Yes. It looks like this. I’ll get the tag info next time…
https://external-content.duckduckgo.com/iu/?u=http%3A%2F%2Fwww.homedepot.com%2Fcatalog%2FproductImages%2F1000%2F8a%2F8a2b6361-75c9-401d-894e-bba7afc67d54_1000.jpg&f=1&nofb=1
Maybe a pressure relief valve.
A relief valve requires a discharge port.
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The dome shaped top with the adjustment screw and the spring retention cap on the bottom are characteristic of that type of valve.
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You are right, I meant a pressure reducing valve.
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Chuck I think you nailed it, looks like a pressure reducing valve.
My guess: Pressure reducing valve.
What was the line coming from and where was it going?
Was it a cold or hot water line.
Now you want facts? I thought this was a guessing game… 
From the limited view I’d GUESS its a PRV not a check valve BUT as several have stated … NEED more info or better pic
It is a Pressure Reducing Valve or what we (including plumbers) around these parts call (simply) a Pressure Regulator. And these will also act as a check valve. So if you see one, the system should have a Thermal Expansion Tank (or other device to compensate for thermal expansion.