# Prototype Mallet Question



## SlateCreek (Jan 2, 2008)

I've worked with 1:1 steam engines, but never an articulated. BUT ... structure and function being pretty much the same, I've got a question looking at the NMRA show thread with all the photos of the new 2-6-6-2. 

On a superheated locomotive, the dry pipe takes a loop through large boiler flues before heading on down to the cylinders. In a "normal" rod locomotive, this is either internal to the saddle, or through two slanted tubes from the smokebox to the valve chest. 

On a Shay, things are a little more complicated, and you can see the dry pipe, insulated, coming from the side of the smokebox to the engine assembly. In a saturated steam Shay, there's no need, it can come straight from the steam dome down to the cylinders ... but on the superheated variety, it generally comes out the smokebox side having gone through the superheater tubes, and back to the cylinders. 

So... I'm looking at the new Bachmann model, and there are TWO symmetrical dry pipes from the smokebox back toward the saddle tank. Photos I've seen of the 1:1 Sumpter Valley 250/251 show this as well ... but that locomotive was a simple articulated, and would have two dry pipes, one to each cylinder assembly. (and two blast pipes as well, but I'm getting ahead of the game) 

Since the Biles Coleman is a compound articulated, with the exhaust from the rear cylinders feeding the intake of the front cylinders .... 

What's the second dry pipe back from the smokebox for? Or do I just not get how these things are plumbed? I don't want to cast any unnecessary aspersions on the designers. 

Matthew (OV)


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## digger (Jan 2, 2008)

Matthew, 

I would suspect that the two pipes you are referring to would carry superheated steam back to the rear set of cylinders, after which it would be exhausted to the front set in normal Mallet fashion. This setup would be easier to maintain than routing them back through the boiler and having them exit directly into the rear saddle. Just my best guess.... 

Ed


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