In the early days of railroading, each passenger car was outfitted with a coal or wood-burning stove to provide heat to the passengers in cool or cold weather. (Air conditioning was, of course, accomplished by opening the windows during this era...) This was both uncomfortable, due to the large temperature gradients across the car and coarse control of the heat output, and very unsafe. In the event of any serious derailment, the outbreak of fire from overturned stoves was almost a certainty.
By the 1890s, stoves had almost entirely given way to heat derived from steam. Railroad passenger cars relied on a relatively low-pressure saturated steam supply to provide heating and cooling functions for the passengers. In the steam locomotive era, this low-pressure steam was in plentiful supply, and was easily supplied to the trailing cars.
Steam heat quickly became a problem, though, once diesel locomotives appeared on the scene. Diesels, producing electrical power rather than steam to transfer energy to the wheels, could not provide the steam required by the cars. Thus, the railroads had them outfitted with devices known as steam heat generators. These units, consisting of a large coil of pipe surrounding a diesel fuel burner, would take water from an auxiliary storage tank on the locomotive and, based on demand, boil it inside the coil and feed the resulting low-pressure steam to the steam line connected to the following cars.
Near the end of the Rio Grande era, a system much more rational for diesels had really started to take over - head-end power (HEP). This was a 3-phase, 60Hz, 480 volt feed off the locomotive, which in turn could be used for heating, cooling, lighting, and all manner of other things in the passenger cars. It had been around in various forms since the dawn of dieselization, but Amtrak began to standardize around it in earnest around 1975 as a replacement to the troublesome steam heat systems. The Grande, however, would opt out of Amtrak from 1970 until 1983, and never owned any HEP-capable equipment.
Only some of the Rio Grande's units were outfitted with onboard steam generators - specifically FTB units in sets 548-551; F3Bs in sets 552-554; F7A units 5571 & 5574; F7B units in sets 555-558; F9B units 5762, 5763, 5772, 5773; and all of the Alco PA/PB sets. By 1953, FTBs 5492, 5493, 5502, 5503, 5512, and 5513 had their steam generators removed and were regeared for freight service.1 This presented a problem as the F units started to age and were being retired, since only a dwindling number of units were steam-capable, the steam generators in them were becoming unreliable, and yet every passenger train still needed at least one.
The solution was to build dedicated steam generator cars. These would allow passenger trains to operate with units not capable of producing steam (such as freight units), and supplement the aging steam generators in the other units.
The first two steam generators, 250 and 251, were built from L-105 tenders in May of 1953. These were presumably built to take the place of the 6 FTBs that were to lose their steam generators that same year. Steam generator #250 came from the tender of L-105 #3703, which was destroyed on 19-Oct-1952 by a boiler explosion south of Sedalia, CO. 251 was constructed from L-105 #3709's tender.
Both 250 and 251 continued to work Rio Grande passenger trains (including the Ski Train) until 1987, when they were removed from service. They remained stored until scrapped in 1991 at Duwald Steel in Denver, CO.2
In the later half of 1965, the Rio Grande created two more steam generator cars out of retired Alco PB-1 locomotives. Reasonable speculation is that these cars were created due to the recent retirement of the steam-capable FTB units and the impending retirement of the remaining F3Bs. This left the railroad with a need for more steam generation capacity.
252 was built first, in July 1965, out of D&RGW PB-1 #6012. Three months later, the other PB, #6002, was also converted, and became D&RGW 253.
D&RGW 252 spent most of its later years stored in Salt Lake City, in order to protect the Rio Grande Zephyr in the event that 253 or the B units' steam generators failed on that end of the system.3 It was removed from passenger service in 1983 and used for stationary steam generation at Salt Lake City until being scrapped with 250/251 in 1991.4
Unlike 252, in the 1970s and early 1980s, D&RGW 253 ran regularly with the Rio Grande Zephyr during the colder months, either to supplement the steam generators in the F units or as the sole source of steam when the train was being handled by freight motors. 253 was then later moved on to the D&RGW's Ski Train once the RGZ operation had ended in 1983.
During September of 1980, #253 underwent a notable visual change - the 3-axle Alco trucks changed out for a pair of EMD 2-axle Blombergs. The decreased weight of no longer having a prime mover, generator, or traction motors eliminated the need for the unit to have the A-1-A axle configuration, and the replacement Blombergs would share standardized parts with all of the railroad's other EMD power. (As a note, obviously the units did not carry traction motors once they were converted to steam generator cars.)
253 went with the Ski Train operation and equipment when they were sold to the Ansco Investment Company in October 1987. By December 1987, it was converted from steam generation to providing 480 volt Head-End Power (HEP) for the new lightweight Ski Train equipment, and renamed "Moffat Tunnel". The car would later become the "Joseph G. Harris", after a former Rio Grande mechanic who was notable also for keeping the Ski Train's older heavyweight cars running. The car, now under the reporting marks SKTX 253, would continue providing electrical power to the Ski Train until the 2000-2001 winter season. By then, the Ansco Ski Train had three dedicated ex-Amtrak F40PH units, each of which was capable of producing its own HEP and 253 was no longer needed. In September 2006, the car was sold to the Algoma Central as the AC 78 and is now used for HEP power their Agawa Canyon trains.
[gSteamGenerators | Here's a linkg] to the galleries of the steam generator cars.
1 Post by Steve Seguine to the D&RGW Yahoo email list, "Re: SG steam generators", on 7-Jun-2006 ⇑
3 Post by Jim Griffin to the D&RGW Yahoo email list, "RE: [DRGW] steam generator 252", on 16-Nov-2006 ⇑