The Big Boy, part 5

In part four of this look at the Big Boy locomotive, I made mention of something a little unusual in steam locomotive design: the notion of a second throttle. Well, that’s actually a joke. The Big Boys didn’t have two throttles. Before I explain, please take a moment to look at the accompanying photograph. The image is a detail portion of a cab backhead shot made by Alco’s company photographer in late August 1941.

Readily visible in the photo is the vertical throttle lever of the type seen on the vast majority of mainline power built after about 1925. However, a glance will probably also bring another also vertical, polished steel bar into view to the left of the main lever, one with an end clearly intended for use as a handle. This is the “second throttle” I alluded to, because it appears similar to the main throttle lever.

Rather, it is the drifting valve lever. Drifting valves had been around for decades prior to designing the Big Boys. During operation, when the steam locomotive throttle is closed while the engine is in motion the halting of steam flow will result in creation of a vacuum as the pistons move back and forth in the cylinders. This vacuum will cause air to be sucked into the steam chests resulting in cinders or sand and other debris entering steam passages, valves and cylinders with the obvious negative results. In addition, closing the throttle completely prevents the vital interaction of steam with valve oil, which is specifically designed into this type of oil, and without which mechanical damage is certain to result, especially over time. Even if valve oil continued to flow into steam chests and cylinders the oil is not working correctly in the absence of steam.

Drifting valves were invented to permit continuation of a flow of steam, even with throttle closed, and prevent the action of vacuum as well as continue proper lubrication. Automatic types of drifting valves were already in use, but on the Big Boys (as well as all of the 1943-44 4-6-6-4s) a manually-operated type of valve manufactured by the Kieley & Mueller, Inc. was utilized. When the engineer pulled the lever the valve released saturated steam which travelled to the steam chests and cylinders ensuring the desired interaction of steam and oil. The intention was extended life of valves, cylinders and related parts. However, one of the disadvantages of drifting valves of virtually any type was that it was found they could stick open, leak, or fail allowing steam to reach the cylinders when it wasn’t wanted. In an engine terminal this problem could result in locomotives moving on their own. It’s easy to imagine dire and expensive consequences. Drifting valves were later removed for this and other reasons. In addition, most engineers already knew to drift engines with the throttle slightly cracked, performing the same service, they didn’t need the valves anyway.

In the year or two prior to construction of the Big Boys American Locomotive Co. had been working toward an improvement in the connection between the front and rear engines of articulated locomotives. Work had already been expended in this direction during design of the early Challengers during 1935-36. Suspension system improvements brought by engineers at Alco during this same period, briefly mentioned in Part 4, had made improvement in this area possible. Previous designs had comprised a sort of massive drawbar, usually made in one form or another of a “Y” in which the upper legs were connected to each side of the locomotive frame providing for vertical movement of the massive pin which passed through the long leg of the Y and into a pocket on the rear engine. The vertical movement of the connection was of absolute importance, but many disadvantages resulted at various points in the arrangement, each of which was subject to wear and required frequent attention. Alco, with its improved suspension, had worked out an almost entirely new connection. First seen on the 4-6-6-4s delivered to Delaware & Hudson a year prior in 1940, the front engine frame casting of the Big Boys incorporated a solid extension into which the pin joining front and rear engines was inserted. No provision for vertical movement was included. This huge “tongue” extending from the rear of the front engine frame, was inserted into an appropriately sized pocket at the front of the rear engine frame casting and the connecting pin set in place. The mechanism was very tight, motion up and downward was almost nonexistent. In order to ensure retention of continuous, measured pressure on the assembly and thereby retain the snug dimensional characteristics the area was very carefully loaded by arranging the spring rigging to impart a load approximating seven tons at the tongue. All vertical movement experienced by the engine while traversing the rails was designed to be managed by the spring rigging. Lubrication of this difficult to reach point was provided for by a connection from the mechanical lubricator located on the left side of the rear engine. Union Pacific would retain this same design through all the later 4-6-6-4s and the 1944 order of the final five Big Boys.

Speaking of lubrication, the Big Boys were at the very front of the race toward ever-improving management of the problems presented by the need for effective and economical locomotive lubrication. Each Big Boy was equipped with four huge Nathan Manufacturing Type DV-7 mechanical lubricators, each providing 36 pints capacity. Two units were located on each side of the locomotives, one on the front engine, one on the rear. Those on the right side provided valve oil to any points requiring that type of lubricant. The two lubricators mounted on the left side fed engine oil to myriad points in the running gear. A total of 123 points received lubrication from these four units. Among the many advantages brought by mechanical, force-feed lubrication was the fact that oil was automatically fed every time the engine was in motion, there was no dependence upon enginemen necessary, and the correct amount necessary was regularly applied, preventing over-oiling which was wasteful and expensive. In addition, many locations in the valve gear, spring rigging, brake rigging and other areas were arranged for hard or soft grease lubrication. In cabs a hydrostatic lubricator provided for lubrication of the steam cylinders of the stoker engine, the use of this lubricator intended as a stand-by when standing for periods of time, at which point the mechanical lubricators would not function as they were driven by movement of the running gear. If all this wasn’t enough the tenders were also arranged with a complete and separate system fed by a fifth DV-7 placed in a box located behind the enginemen’s grip container built into the front corner of the tender immediately behind the ladder leading to the cab. The stoker drive mechanism was also fitted with grease and oil cups at various locations.

A great deal of pipe usage was saved by utilizing New York Air Brake’s new intercooler assembly. Rather than the usual setup of long loops of piping seen along the boilers (although Union Pacific had long utilized placement horizontally below running boards, when practical, for sake of locomotive appearance), the finned pipes forming the “radiator” of the intercooler system were readily visible above the pilot deck, placed inside the front deck handrails. This location would prove slightly vulnerable. In fact, 4001 had not made it 300 miles west from Omaha during delivery to Ogden, Utah for service. A photo made in North Platte, Neb., during that trip displays obvious damage to the piping on the left side of the locomotive. The addition of protecting plates surrounding the finned piping was made to 4000 for the delivery trip west from Alco but this was not continued in service.

This piping assembly also formed a part of what was without much doubt one of the more distinctive “front-ends” on any large locomotive. The imposing pilot (especially in original configuration), the large sheet metal shield placed ahead of the air pumps and pilot deck, the number plate and “winged” headlight with number indicators, the cast iron number plate and huge smokebox door with bell mounted above, the classification lamps and indicator boards all served to create an unmistakable look which is among the more readily recognized around the world.

Next time: The effect Big Boy had within the industry and the public at large.