EMD SD24
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 UP #408 at the company's Portland, Oregon, Albina Yard in July, 1968. The unit's roof-mounted "torpedo tube" air reservoirs, a signature feature, are clearly visible just aft of the locomotive's cab. |
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| Power type | Diesel-electric |
|---|---|
| Builder | General Motors Electro-Motive Division (EMD) |
| Model | SD24 |
| Build date | July 1958 – March 1963 |
| Total production | 179 A units, 45 B units |
| AAR wheel arr. | C-C |
| Gauge | 4 ft 8½ in (1,435 mm) |
| Power output | 2,400 hp (1,800 kW) |
The EMD SD24 was a 2,400 hp (1,800 kW) C-C diesel locomotive built by General Motors' Electro-Motive Division of La Grange, Illinois between July, 1958 and March, 1963.[1] A total of 224 units were built for customers in the United States, comprising 179 regular, cab-equipped locomotives and 45 cabless B units. The latter were built solely for the Union Pacific Railroad.[2]
The SD24 was the first EMD locomotive to be fitted with an EMD turbocharged diesel engine, several months before the four-axle (B-B) model GP20. Power output was substantially higher than the 1,800 hp (1,350 kW) of the concurrent Roots blower-equipped SD18s with the same engine displacement.
In terms of sales, the SD24 was only a moderate success, and few had long service lives in SD24 configuration (though many rebuilds are still in operation), but the SD24 was a milestone in EMD locomotive development and the forerunner to today's high-powered six-axle locomotives.[2]
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[edit] Options
Optional equipment that could be specified by ordering railroads included multiple unit controls, a steam generator, dynamic brakes, winterization equipment, an air signal line, and hump control,[2] but in actual fact almost all delivered SD24s were very similar in configuration.
The standard fuel tank offered a 1,200 US gallon capacity, while 2,400 or 3,000 US gallon tanks were optional. In practice, all SD24s ordered had the 3,000 gallon tank except for the last built, Kennecott Copper's single locomotive. In order to provide room for a larger fuel tank, the air reservoirs were relocated on the roof just behind the locomotive's cab. The tanks were known as "torpedo tubes" due to their long, thin design. Factory-installation of these tanks was peculiar to this model locomotive.
Winterization included a winterization hatch over one of the fans.
Either a low or high short hood could be ordered; in either case, the short hood was front by default. The Burlington and Southern ordered high short hoods; all others were low. Low short hoods from the factory had a pronounced downward slope of the top towards the nose, as did those of the contemporary GP20. Many of the high short hood units had their noses chopped later on, often as a consequence of rebuilding; these as a rule have flat-topped short hoods.
[edit] Rebuilds
As the SD24 locomotives aged, they began to develop reliability problems, especially electrical ones.[2] In addition, the extra maintenance requirements of the turbocharged engine were acceptable when they were some of the most powerful locomotives available, but in secondary service, they were an expensive way to get 2,400 hp. Thus, a large number of SD24s were rebuilt by various owners to extend their lives.
[edit] Santa Fe SD26
From January, 1973 through January, 1978 the Atchison, Topeka and Santa Fe Railway rebuilt its fleet of eighty SD24 locomotives, naming the resulting type the SD26. The rebuild boosted the power output of the locomotives by replacing the 16-567D3 engines with 16-645E3 models. Other work improved the reliability by replacing the entire electrical systems, and replacing the multiple body-side vents with a central air filtration system. The large box fitted high on the body behind the cab for the air filters required relocating the "torpedo tube" air reservoirs further back on the long hood, and gave the SD26 a noticeable "hump-backed" appearance.
[edit] Union Pacific SD24m
The Union Pacific Railroad modified three SD24 locomotives experimentally to see if it would be worthwhile to upgrade their fleet of 30 such locomotives.[3]
Unit 410 received the most minor modification: upgraded air filters.[4]
UP 423, however, was substantially rebuilt to UP 3100 in August 1968 with a constant-speed 16-645 3,000 hp (2,240 kW) prime mover, a new alternator and new traction motors. With the constant-speed engine, speed control was via changing the level of excitation of the alternator; the traction motors were permanently wired in parallel. New, variable dynamic brakes were also fitted, as was a self load feature enabling testing under load without an external electrical load apparatus. This latter feature became standard on later locomotive models. The constant-speed prime mover, on the other hand, was not successful enough to duplicate. The locomotive was from 1975 used as a heavy switcher at UP's North Platte, Nebraska hump yards, a fate common to UP's other surviving SD24s.
UP 414 did not receive as major a modification as #423, but it was refitted with a 16-645 engine, AR10 alternator and Dash Two electrical cabinet in May 1974, making it effectively a EMD SD40-2. This was a testbed for a proposed upgrade of all UP's SD24s, but UP decided not to go ahead with the work. Both UP 3100 and UP 414 were classified as "SD24m" by the UP, but some UP internal documents class UP 414 as a "SD24-4".[3]
[edit] Original purchasers
| Railroad | Qty | Road numbers | Notes | |
|---|---|---|---|---|
| Santa Fe | 80 | 900 – 979 | Pan Am Railways purchased 35 in 1986, 2 remain in service today (621,643). The rest were scrapped, except for the 631 which was destroyed enroute. | |
| Burlington | 16 | 500 – 515 | High short hood | |
| General Motors-EMD (demonstrators) | 4 | 5579 and 7200 – 7202 | 5579 first SD24 build, high hood; 7200–7202 next to last built, low hood. All sold to UP as numbers 448 (EMD 5579) and 445 – 447 (EMD 7200 – 7202) | |
| Kennecott Copper | 1 | 904 | Last SD24 ordered, turbocharging required due to high altitude operation. Small fuel tank fitted, only SD24 not to have "torpedo tube" air reservoirs. No MU fitted. | |
| Southern | 48 | SOU 2502 – 2524, CNTP 6305 – 6325, NO&NE 6950 – 6953 | High short hood | |
| Union Pacific | 75 | A units 400 – 429, B units 400B – 444B |
[edit] References
- ^ Pinkepank, Jerry A. (1973). The Second Diesel Spotter's Guide. Milwaukee, WI: Kalmbach Publishing Co.. ISBN 0-89024-026-4.
- ^ a b c d Diesel Era staff. "EMD's SD24". Diesel Era 9 (3): 10–29, 51–63.
- ^ a b Strack, Dan. Union Pacific EMD SD24s. Utah Rails. Retrieved on 2006-11-27.
- ^ Strack, Dan. All-Time UP Diesel Roster, Part 5. Utah Rails. Retrieved on 2006-11-27.
[edit] External links
- EMD SD24 Diagram at the Illinois Railway Museum official website.
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