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Manufacturer and instruction sheet
I figure someone has seen this on a system before, it dates from 2006 in my case. "Simplex" is the brand.
I'm looking for the manufacturer or a user sheet for this gauge, which is also some sort of valve.
It's the valve function that is obscure, and I'd like to read or hear what type and how it is intended operate on a primary loop for a modcon boiler.