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Mallet and his Grand Design
The name "Mallet" comes from the designer of articulated compound locomotives - Anatole Mallet (pronounced "Malley"). To be a true Mallet locomotive, the engine must be articulated and be a compound, meaning the steam is used twice in separate cylinders. A simple explanation of compounding follows:
The high pressure cylinders use the steam first and are the smaller of the two sets, the steam is then passed to the larger low pressure cylinders where the steam is used again. It was supposed to be more efficient, but the complication was maintenance intensive, and the locomotives were actually slower than simple expansion locomotives.
The creation of the first Mallet was simply one solution for the never-ending quest for more horsepower. To achieve more horsepower an engine requires more heating surface and grate area. More heating surface means larger boilers. A larger boiler means a longer, heavier locomotive with more boiler capacity and the greater tractive effort exerted by a larger number of drivers. There was one real problem in order for this idea to work on rails... the fact the mega-engine would need to round curves. So the articulation principal of Anatole Mallet's was very appealing to the buyers of the first Mallet, as well as the improved thermal efficiency from Mallet's approach to compounding.
The first Mallet locomotives (early 1900's) were designed to meet the needs in Europe. The US Mallets which came later required a number of innovations to deal with an engine that is typically twice the size of its European counterpart. Originally these engines were used as pusher engines on grades as steep as 2.5%. In addition to solving traffic congestion the Mallets were very fuel efficient, reducing the amount of fuel used per ton mile by 46%. (for more Mallet info see http://www.ironhorse129.com/Prototype/Mallet/Baldwin65/baldwin_record_65.htm)
It is easy to imagine that such an impressive engine as Molly may have been put to use on the most powerful runs of the day, cresting the limestone rises of Kirkwood with a mile-long line of coal freight, but she didn't. The fact is Molly was a blue-collar worker, through and through. Her sheer massiveness made her ideally suited for effortlessly shuffling the high tonnage in endless strings of cars, breaking-up and building trains at Missouri Pacific's yard hump in St. Louis and Dupo, as well as tending transfer drags... a sight that must have truely been awe inspiring to witness. Nothing else owned by the road approached her, Molly was the single one of her kind on the system.
Other than her size, Molly was your typical MoPac steam engine with all the standard features. In our earliest photo, on the MPHS website (mopac.org) we see Molly as she looked prior to the merger of the MP with the Iron Mountain. Under her cab window in small capital letters is the name "IRON MOUNTAIN", on her middle dome is the number "4000". Her boiler is a shiney black with her smokebox a flatter graphite color. Notice she had smaller domes and oil-powered headlamp arrangement.
Photographic evidence shows that as time went by, beyond the merger into Mopac, she recieved a number of modifications. Besides regular shopping and rebuilding dictated by the railroad, steam crews were consumate tinkerers and constantly tweaked and made improvements to their charges, much more so than their diesel counterparts. All steam engines became unique and one of a kind pieces of machinery.
Most noticeble of Molly's changes are the larger forward and rear domes, additional "plumbing" mounted along her flanks, a spark arrester/flap for her smokestack, and a more modern electric headlamp. Her tender seems to be the original car, which also recieved new trucks and a "doghouse" for the head brakeman.
In a 1936 photo (MPHS Eagle, Vol. 19 No. 1) she's seen painted in the conservative Missouri Pacific colors - an all-over glossy black boiler and a brighter graphite, almost aluminum on the smokebox and firebox. A large brushed aluminum "4000" was applied under her cab window with "M.P." sublettering. The sublettering was also placed on either side of her squat forward dome.
The Wallin Collection photo, also on the MPHS website (mopac.org) apparently shows the locomotive at a later date, covered in sooty grime - both the smokebox and boiler weathered to the same shade.
on MO&G / KO&G 2-6-6-2 Mallets
Wheel Arrangement: 2-8-8-2
Tank or tender type: Rectangular tender
Builder / date: Baldwin - 1912
Driver diameter: 55"
Boiler pressure: 200 PSI
Cylinder dimensions: 26x32 LP / 40x32 HP
Tractive effort: 94,400
Service History: 1912 to St. Louis Iron Mountain & Southern as #4000 ...to Missouri Pacific RR. as #4000. Assigned to St. Louis and Dupo hump duties entire career.
Disposition after MPRR service: Sold to...? Scrapped... ?
Pictures: MPHS website
trainweb.org/screamingeagle l Last Update to this page: 29 May, 2008
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