Steam & Excursion > Steam Engine Domes

Most steam engines that I have seen have two domes on top of the boiler.
I believe the first one was for sand, but what was the second one for?
Thanks

Hal

Some locomotives had more than one sand dome, especially switchers or on logging railroads that ran their locomotives as much in reverse as forward. Passenger and mainline freight locomotives spent the majority of their time running forward so they didn't really need a great rear sanding capability.

The steam dome collects "dry" steam. Within the dome is the throttle valve which regulates the steam admission from the boiler to the dry pipe and, ultimately the cylinders. An auxiliary dry pipe would tap steam for use by accessories such as a hydrostatic lubricator. The steam dome is also a convenient place to locate pop safety valves and a whistle.

As boiler diameters increased in size, the builders had to use shorter domes due to bridge and tunnel clearances. Short steam domes left less room for the increasingly larger throttle valves. That and higher boiler pressures led to the development of the multiple valve throttle, also known as a front end throttle. Big engines like the 700, 765, 844 and 4449 have tall boilers and front end throttles so their steam domes don't look as camel humped as smaller engines.

Wikipedia has a simplified illustration of a superheated steam locomotive with a dome throttle here:
http://en.wikipedia.org/wiki/Firebox_(steam_engine)

Hope that helps. I'm sure others will add.

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SP&S 700 is a great looking Northern...nice photo....steam loco's look best in long light, with cool temps and high humidity.



Edited 1 time(s). Last edit at 12/02/12 20:00 by OKTrainboys.

Maybe "picky" but any boiler (locomotive) has but one DOME, the steam dome where steam collects for distribution to various components, most notably, the throttle. All other "lumps" are boxes such as the sand box.

qman

qman Wrote:
-------------------------------------------------------
> Maybe "picky" but any boiler ...

All other "lumps" are boxes such as
> the sand box.
>
> qman


Or, turrets.

-LD

qman Wrote:
-------------------------------------------------------
> Maybe "picky" but any boiler (locomotive) has but
> one DOME, the steam dome where steam collects for
> distribution to various components, most notably,
> the throttle. All other "lumps" are boxes such as
> the sand box.
>
> qman

If it doesn't have steam in it, it's a box, not a dome.