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came in 1908, No. 24 in 1909, and Nos. 27- 35 between 1910 and 1931. Nos. 8, 24, and 25 were fitted with smaller air reservoirs of 28¹/₂ cubic feet capacity. The 0-4-0CA’s were used for a variety of
duties including hauling explosives, mine timbers, and drill steel from the surface to the underground workings, and for pulling trains of one-ton ore cars through the drifts and tunnels. They also hauled miners to and from the working faces. The five-ton engines were too big for sever-
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al tunnels, and Porter worked with Homes- take to develop a 3³/₄-ton 0-4-0CA, the first of which, No. 13, came on the property in Janu- ary 1908. It was 7′-11″ long and three feet wide, with a reservoir capacity of 20.5 cubic feet. When pressurized to 900 p.s.i., its tiny 5″×8″ cylinders could muscle a train of 12 cars. Like the others it was cabless, but the rear deck was removable to allow it to be moved between levels aboard the elevator. Homestake was so impressed with it that they ordered five more in late 1908 (Nos. 14-19), and went back for three (Nos. 21-23) in April 1909, allowing the last horses to be retired. By 1910, Homestake had over 100 miles
of underground track in service, and addi- tional air piping and charging stations had been installed on all levels of the mine. To keep up with the ever-increasing require- ments for compressed air, the company had installed a steam driven, four-stage Inger- soll-Sergeant compressor in 1906 that dis- charged 1000 p.s.i.g., the largest compressor in the world at that time. An additional 22″ gauge locomotive, Homestake No. 9, was purchased for the surface tramway in 1907. It was an 8¹/₂-ton 0-4-0CA with 7″×12″ cylinders and a cab to shelter the operator. Number 9 was most of- ten used as the shop motor at the mainte- nance building where Homestake over- hauled the locomotives. By the late 1920s, Homestake’s original
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22″ gauge 0-4-0CA was worn out, having been in continuous use for nearly 30 years. The company had purchased an additional air motor, No. 20, for surface use in 1908, but it mainly worked as a switcher. Thus, in 1927 Homestake ordered a new locomotive from Porter to replace No. 1 on the surface tramway, which was No. 1A, the first (and only) two-stage air motor it would ever own. The development of two-stage pneumatic locomotives had been a technological leap for the mining industry. Ever since the first single-stage pneumatics had taken to the rails in the 1870s, manufacturers had been working on ways to increase their running times. One way was to use the air twice. You may remember from Part 1 that a sin- gle-stage locomotive uses air just once. It’s taken from the main storage tank, reduced in pressure, and piped into an auxiliary reser- voir. When the throttle is opened, the air travels from the auxiliary reservoir directly to the cylinders, where it partially expands, moves the piston, and drives the wheels be- fore being exhausted to the atmosphere. The problem is that when high pressure compressed air expands in a cylinder, the temperature drops around 140 degrees and it loses much of its pressure. (For this rea- son, special low-temperature cylinder oil had to be used.) Using the air a second time makes the situation worse, further decreas- ing both pressure and temperature. Never- theless, many builders dabbled with com- pound engines that used the air first in a
high pressure cylinder and then in a low pressure cylinder in a quest to gain efficien- cy. Most such efforts met with failure, be- cause by the time the air reached the low- pressure cylinder it had lost much of its energy and was too cold to do much work. Also, no lubricants could stand up to the ex- treme conditions; even the best Arctic oil froze solid. One way to combat the problem was to re-
heat the partially expanded air as it moved between the high pressure and low pressure cylinders (or “stages”). Surrounding the air with hot water was one method; reheating it with a kerosene or coal fire was another. Neither method worked particularly well. Baldwin experimented with Vauclain Compound cylinders on its pneumatics, building its first in 1897 for Philadelphia & Reading Coal & Iron’s Alaska Colliery at Mount Carmel, Penn. It was successful enough that four more were built, but they suffered from lubrication and freezing is- sues, and were no more powerful than com- parable single-stage models. At the beginning of the 20th century, building a workable compound air locomo- tive seemed to be an elusive prize, just out of reach. The genius of mining engineer Charles B. Hodges made the compound (or two-stage) pneumatic locomotive possible. In the early 1900s, Hodges developed an at- mospheric reheater that used ambient air pulled through a heat exchanger to heat the air between the stages, substantially in- creasing the range of pneumatic locomotives between fills. The Hodge reheater was de- scribed in the 1914 Porter catalogue: “It con- sists of a cylindrical steel casing filled with aluminum or brass tubes of small diameter, around and between which, guided by the baffle plates, the air passes. The final ex- haust air from the low pressure cylinder is utilized in an ejector apparatus, similar to the smoke stack and exhaust nozzle of a steam locomotive, to draw a rapid current of the surrounding atmospheric air though the small tubes.” By drawing warm outside air through the external reheater, the chilled air from the high pressure cylinder was warmed as it moved between it and the low pressure side. To make up for the loss of pressure, which dropped to 50 p.s.i. between the stages, the surface area of the low pres- sure cylinder was increased substantially in order for it to do the same amount of work as the high pressure side. Porter realized the possibilities afforded
by Hodge’s invention and purchased the rights to his patents. It began testing Hodge interheaters in 1904, and four years later delivered its first two-stage air locomotive to the Susquehanna Mining Co.; it was a rous- ing success. Because the air was used twice, the company reported that the locomotive “showed a gain in efficiency of over 50 per cent, and a saving in compressed air con- sumed of over 30 per cent.” While two-stage air locomotives were complex machines and significantly more expensive than their sin- gle expansion brethren, because they used less air, smaller air compressors could be used and so the overall cost of a complete air-haulage system was less. Homestake No. 1A was delivered and set
up for service in early 1928. Weighing 12¹/₂ tons, it sported twin interconnected air tanks with a combined capacity of 137 cubic feet; a main pressure of 1000 p.s.i.; and an auxiliary reservoir pressure of 250 p.s.i. It
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