Margaret (SP fan) Wrote:
-------------------------------------------------------
> Tom --
> But I thought the FW heater heated the water
> enough that it would not thermally shock the
> boiler, but the injector puts cold water directly
> into the boiler from the tender with no heating,
> and that a steam locomotive crew should never use
>
> the FW heater when the loco was standing still, as
>
> (for some reason I cannot now remember) a FW
> heater
> cannot work well when the locomotive is standing
> still,
> and the injector is used when standing still.
> That is what I learned from being part of
> "Project
> 2472" and listening to the old heads.
>
> That green fireman probably had the injector on
> for much too long.
>
> Corrections from knowledgeable folks cheerfully
> welcomed!
>
> Margaret

Margaret, when you use an injector, live steam from the boiler is used to force fw through the
check by virtue of it's energy. Although that water does contain some heat due to the addition
of the steam, it is still at less temp than the water in the boiler.

However, a FW heater depends on exhaust steam to add heat. If the locomotive is sitting on the
spot with no discernible exhaust, then there is no heat at all being added and it is truly cold
water that is entering the boiler. Live steam from the boiler powers the steam piston which
runs both the cold and hot water pumps, but the direct heating comes from exhaust steam. A FW
heater captures some of the waste heat that would otherwise be lost at the stack.

It is possible to sag the pressure in the boiler with overuse of the injector while standing,
but in this case, the kid left the pump running while sitting on the spot.