I want to throw out this resource here. I mentioned David Fletcher (Australian G gauge modeler) who did a series of “Master Classes”. One of them in particular is his 2-6-0 Mogul build. Chapter six of that class, found here is a great resource to locomotive plumbing and how to model it.
I am relying on his description in that class for this next part. A final piece of plumbing coming off the turret is what he refers to as the blower pipe. What the blower pipe does is act like a super charger. Some back ground; we talked about the fire being pulled through the boiler by draft created when the fire is made in the fire box and smoke exhausted out the stack. A way of super charging this draft is to exhaust the steam from the steam chests/cylinders into the smoke box. This is one of the “other” things I said the smoke box does. Steam enters the bottom of the smoke box through the saddle. I will talk about this more when I talk about the cylinders. But for now that steam enters the bottom and rushes out the top of the chimney. It is white the “smoke” from a locomotive often times is more white/grey than black. Remember our friend the venturi? Well that steam rushing by the fire tubes creates a venturi and increases the draft by sucking the fire through the tubes, in effect we can think of this as a turbo charger. But how do we create this venturi effect when the throttle is off and no steam is going to the cylinders? We still want to rev up the engine but we don’t want to go anywhere. We want to do this so we can build up steam prior to taking off? Enter the “blower valve and piping”.
A valve is fixed either to the turret or the side of the boiler with a pipe that runs to the smoke box. and into the bottom of the chimney. At idle the valve is opened and steam is allowed to rush down this pipe and out the chimney. As it rushes out the chimney we again get a venturi that pulls the hot gas through the fire tubes and out the chimney. It increases the draft of the locomotive and in turn raises the temp in the boiler which in turn increases the pressure. So at idle the locomotive can be “given a little gas” and be “reved up” prior to actually opening the throttle and driving the locomotive. Prior to the blower valve a locomotive had to get under way to start the turbo charger effect. This valve and piping most typically was on the fireman’s side and ran under the walks and it is a reason its hard to find a picture of. That and not all locomotives employed a blower system.
That should do it for the basic stuff coming off the back head.
