It is visible in this DPL Bob Richardson picture.
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digital.denverlibrary.org]
At a guess I'd say what ever the poor RGS had on hand to effect a repair, not having noticed anything like it before. Note that it is bolted in place not riveted as usually was done.
41 is shown out of service 10 years prior to Bob's '51 photo, tenderless "awaiting repairs to its tender's "leaky cistern" R.G.S Story V-XII pg 82
EDIT:
Waterleg Valve inspection port?
#278 has it too.
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digital.denverlibrary.org]
Chris
in New Zealand
Edited 2 time(s). Last edit at 06/25/2014 05:15AM by Chris Walker.