by Emmett Smith
Believe it or not, this 1947-8 Norfolk & Western 4-8-0 Mastodon switcher (!) even after experimental re-shopping didn’t have superheating.
When I first noticed this Norfolk & Western Railway experimental unit the night before last, I thought I’d stumbled onto another operation similar to that of Delaware & Hudson Railroad’s President L F “High Pressure” Loree. I’d written up at the beginning of September, this year, his experiments of the late 1920s and the early ‘thirties:
However, the N&W class M locomotives were primarily switch-engines; it included a fleet of 4-8-0 Mastodon “Twelve-Wheelers” and ranged from Class M to M2c. *
A lengthy 2002 discussion of the N&W 4-8-0s ensues, at:
The following figures ** may be of interest, especially as detailing over time an individual railroad’s bureaucratic and technical development of a class or engine-category.
— [new number series — does not apply]
94, 95 [ — old series]
(Changed to O-19 class by 1902)
375-499 [ — new series]
(Stephenson or Baker valve gear)
(Walschaerts valve gear)
(Saturated as built – Modified with superheater – Walschaerts gear)
(“Automatic” 4-8-0 Switcher) 1100,1112
(As rebuilt with Bailey water and combustion controls *** – Saturated – Induced draft turbo fan **** – Tender capacity – 29 tons, 11,000 gals)
(Superheated – Baker gear)
Here we are concerned with M2 #s 1100 and 1112. According to this roster they were rebuilt with Bailey Meter water and combustion controls which supposedly automatically controlled the boiler water-level per draft-rate, and so they were called “Automatic Switchers.”
Oddly enough, especially as this work was done according to Drury in 1947-8 ***** and long after superheating had been brought in, more than a generation before, saturated steam only was used and there was apparently no superheating! Therefore, the elongated smokebox which to my eye is particularly elegant, was enlarged to house a draft-powered turbo fan.
There are three types of mechanical draft ******:
Induced draft — This is obtained one of three ways, the first being the “stack effect” of a heated chimney, in which the flue gas is less dense than the ambient air surrounding the boiler. The denser column of ambient air forces combustion air into and through the boiler.
The second method is through use of a steam jet. The steam jet oriented in the direction of flue gas flow induces flue gasses into the stack and allows for a greater flue gas velocity increasing the overall draft in the furnace. This method was common on steam driven locomotives which could not have tall chimneys.
The third method is by simply using an induced draft fan (ID fan) which removes flue gases from the furnace and forces the exhaust gas up the stack. Almost all induced draft furnaces operate with a slightly negative pressure.
Forced draft — Draft is obtained by forcing air into the furnace by means of a fan (FD fan) and ductwork. Air is often passed through an air heater; which, as the name suggests, heats the air going into the furnace in order to increase the overall efficiency of the boiler. Dampers are used to control the quantity of air admitted to the furnace. Forced draft furnaces usually have a positive pressure.
Balanced draft — Balanced draft is obtained through use of both induced and forced draft. This is more common with larger boilers where the flue gases have to travel a long distance through many boiler passes. The induced draft fan works in conjunction with the forced draft fan allowing the furnace pressure to be maintained slightly below atmospheric.
Neither the forced or balanced draft-systems above would appear to apply in this case, and while I am not clear on all of this as yet, it would seem that the blast-pipe gases were directed through a turbine on its way to exhaust, and that this was intended to pull gases from the furnace and thus increase draft. It was evidently intended to insure a more steady rate of both fuel-consumption and steaming.
It may be then that this in turn was the point of the whole undertaking, to see if improved steaming draft-improvements could cause an engine to perform as powerfully as through superheating. If so, of course, then the final company decision would have to have taken into account both inital cost-differences of systems, and later maintenance costs. I have so far not dug up anything on the railroad’s findings from its experiments with these two engines; all we have to go on so far is the rather obvious fact that no more were built by N&W in any wheel-array.
According to Drury these engines were experimentally shopped in 1947-8 by N&W, as noted above, oddly late in view of their limited steaming capacity and so on! That suggests to me that they were a carefully allotted control-pair, dedicated for the turbo trials. I would be willing to bet a pinch will get you a pound that there were a whole series of modifications along the lines described above, including possibly of so-called “balanced” drafting! More clearly needs to be done to elucidate this interesting example of corporate history, especially in the case of so excellent technically a railroad as the N&W was.
[to be continued — ed]
*** — In 1978, Bailey Meter changed its name to the Bailey Controls Company to reflect company evolution. Bailey Controls Company celebrated 75 years of excellence, 1916-1991. In 1989, Bailey Controls merged with Italy’s Elsag Group to form Elsag Bailey Process Automation.
**** — Most boilers now depend on mechanical draft equipment rather than natural draft. This is because natural draft is subject to outside air conditions and temperature of flue gases leaving the furnace, as well as the chimney height. All these factors make proper draft hard to attain and therefore make mechanical draft equipment much more economical.
***** — Drury, George H, Guide To American Steam Locomotives, Kalmbach (Waukesha, 1993), pp 306-7
****** — http://en.wikipedia.org/wiki/Boiler
[Emmett R Smith
[all rights reserved & all other rights revert to holders]
[11 October 2009]