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Detail of the ID plate on the valve on the top cover of the steam generator. It reads

Southwestern Valve Corp

Santa Ana. California

Mod.: PV21A Ser. No.: 197

Part No.: 203783

24 Volts DC <blank> Amps

Additionally, there's a stamp which reads "Cure Date Jan '56".

Time picture taken	Sat Jan 19 16:57:58 2013
Location picture taken	Home of Mark Wells Northern Alabama