Superheaters?

[farmallzach]

I am going to have a boiler built for my 3/4 inch scale 4-8-4 and was wondering if a superheater would be beneficial for a locomotive of this size? The plans call for one that is just a coil of copper tubing in the smokebox, but I would like it to be more prototype and have them in the flues, or am I better of to keep it simple? Thanks, Zach

[Dan Rowe]

Zack,
You have to ask the question what do you intend to accomplish with superheaters?

It is my opinion that most of them do not really add much superheat. The small copper tube you mentioned is certainly in this group.

The real purpose of superheaters is to increase the efficiency of the loco. If this is your goal a well designed superheater can help some. Also a feed water heater can improve efficiency.

The down side is both superheaters and feed water heaters increase maintenance. In full size practice the extra cost of maintenance was offset by reduced fuel costs. I do not think the equation scales well.

Superheaters will require larger flue tubes and make cleaning the tubes with a tube brush impossible. It also makes the smoke box a lot more complicated. If you actually reach some degree of superheat you will have to check the ratings of your steam oil. A different blend is needed for the higher temperature.

My opinion is that they are not really worth the extra effort.
Cheers Dan

[Harlock]

I would also chime in with the idea that it would not be worth it for the small scales unless you really really just wanted to do it for fun. But the tube diameters vs. wall thickness will create some pretty small spaces as Dan says will be very hard to maintain.
'
The one saving grace is if you're firing on propane or butane then the cleaning wouldn't be that much of an issue.

[doug]

Zach,

I'll add comments from my experiences in 7.5" gauge, and perhaps it will be info useful to you.

I have seen where superheaters made a difference between a poorly operating loco and one that operated with some snap to it. The biggest contrast was a pair of mallet locos built by different builders. The one without superheat only pissed hot water out of the low pressure cylinders, the steam was not hot enough to keep from condensing. The other one had superheaters that went all the way through the firebox to the back head. Not only did the low pressure cylinders produce work, the loco operated with a clear stack, and no shower of condensed steam.

I intend to superheat the Climax and Willamette that I am building. Both had long exhaust and steam pipes to the cylinders, and I am expecting a wet stack in cooler weather if I run them saturated. Experience with other locos has proven to me that this is the direction I need to go. I consider any extra efficiency gained from the superheaters in these locos to be a bonus, but just having dry steam at the cylinders will be a plus.

Regards,

Doug

[gwrdriver]

I can fully confirm Doug's experiences above as they have been my experience also. I think of it as steam drying rather than superheating although it is superheating, just to a small degree. A little drying will turn a lethargic, slobbery engine into one that is more of a pleasure to drive. Does it involve extra work? Yes, but not as much extra work as having to retrofit an engine with S'heater tubes.