Heating Water in the Tender

[Anonymous]

I remeber there being a thread about this a while back, but I can't seem to find it.

 

I was recently reading George H. Baker's "Firing with Bituminous Coal (Fireman's and Brakeman's Preporatory Instruction, Part 2)", Published 1927.

I recall Mr. Baker saying that when the engine is sitting, it may be wise to "pre-heat" the water in the tender by blowing boiler steam back into it, the pre-heated water, even only if heated a few degrees, would greatly lower the amount of fuel needed to boil it later.

Sorry for a late response,

S. Connor

[Wizlish]

S. Connor

I was recently reading George H. Baker's "Firing with Bituminous Coal (Fireman's and Brakeman's Preporatory Instruction, Part 2)", Published 1927.

I recall Mr. Baker saying that when the engine is sitting, it may be wise to "pre-heat" the water in the tender by blowing boiler steam back into it, the pre-heated water, even only if heated a few degrees, would greatly lower the amount of fuel needed to boil it later.

This is true.  But there are substantial limits on the amount of 'feedwater heating' that can be done with tender water, as a long string of experiments over the years have demonstrated...

My own opinion is that bringing the tender water up to around the point where domestic hot-water heaters show best efficiency, somewhere just below 120 degrees F, would make "best" sense.  Above that you would need to insulate the cistern space, which would be difficult in a number of practical respects on "legacy" tender designs such as water bottoms.  You don't want to get the tender water hot enough to cause increased problems with injectors, let alone with water reaching saturation temperature and requiring overpressure (and the regulation of unfired pressure vessels that would go with that!)  My father said that when he was young, he had the bright idea that pressurizing hot tender water in this way would help with the low-pressure pumping of water into a feedwater heater.  That scheme founders when an injector is mandatory practice... there are other reasons, but that one is the most significant.

One pound of saturated steam will bring roughly six pounds of water to the boiling point, if I remember correctly.  That means not too much exhaust steam will quickly and neatly heat up the cistern water.  This was no mystery to designers even in the 19th Century, but it had to be periodically 'rediscovered' by some...