Can anyone shed light on the different numbers and positions of particularly the top washout plugs or holes on A3 boilers which are so visible but nobody has explained them that I know of? I can see at least 3 variations:
1. 3 equally spaced washout plugs along the top of each firebox on early types
2. 4 equally spaced plugs later
3. 5 unequally spaced plugs on most or all late versions.
Do these correspond to boiler types 94, 94HP and 94A respectively?
On a few engines there's an additional lower plug on the front edges of the firebox: which boiler type was this?
A3 boiler washout plugs
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