Rich Melvin posted:Mixed Freight posted:The print also says it had a "Foam Meter". Was this to measure the trackside railfan's excitability as the engine went past them?
LOL!
Good one!
The "Foam Meter" would help the fireman identify if the boiler water was foaming. This was a potentially dangerous condition because when it happened, the water turned all light and foamy. That's not conducive to conducting heat away from the sheets or making steam. Water with a high level of undissolved solids could cause this.
When it happened, the cure was to back off the throttle and turn on the feed water pump (and the injector, if needed) to get a lot of cold, fresh water into the boiler as fast as possible. That would temporarily drop the steam pressure and put the boiler through some thermal stresses, but it was better than losing the crown sheet and an explosion!
Yeah, I highly suspected it had something to do with some sort of boiler water foaming problem. Thanks for explaining it further, always good to learn more. 
