Little help with identification and purpose

[Bill Anglin]

I found this in the home I inspected today. It looks like an expansion tank beside the main shut off valve but I'm unsure. I cant think of why you would need one there. Any help is appreciated. 1941 Craftsman

[John Arnold]

Water hammer reducer is my guess.

[Nick Ostrowski]

Water hammer reducer is my guess.

I'd say the same. Also looks like galvanized supply piping downstream of the meter.

[Bill Anglin]

That makes sense. Thanks guys

[Tony Watson]

Looks like an old filter, (ice maker filter) that has been plugged.