The dawn of tunnel ventilation
It was a natural progression from mines to tunnels. Many of the early tunnels were beset with ventilation problems during their construction. Those experienced by Marc and Isambard Brunei during their work on the first Thames tunnel are known from our school history lessons. The need for permanent ventilation did not become apparent until the 1870s and the use of the already established manufacturers of mine fans was an obvious solution.
One of the Great Western Railway of England’s pioneering achievements in the field of civil engineering was the building of the 41/2 mile long tunnel beneath the River Severn estuary. At the time of its construction it was the world’s longest underwater and the first to connect two countries — England and Wales.
Work commenced in 1873 and the inaugural goods train ran through on the 9th January 1886, carrying South Wales coal bound for the metropolis. Passenger traffic did not commence until the December, awaiting the construction of some connecting lines, thus proving that the Channel Tunnel is unique in nothing.
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Figure 1.27 River Severn Estuary tunnel
During construction, following the death from inflammation of the lungs of two men who had been working in one of the headings, a Guibal fan having an impeller diameter of 5.5 m and a width of 2.1 m was installed. This was fitted to the top of the new pit shaft at Sudbrook (Figure 1.27). When the tunnel was completed a larger Guibal fan having an impeller diameter of 12.2m and a width of 3.7 m was installed for permanent ventilation. This was steam engine driven, the supply being from three Lancashire boilers each 2.1 m diameter by 7.9 m long. The maximum rotational speed of the fan was 60 rev/min, but less than half this was stated to be sufficient for normal operation.
Whilst the contractor, Thomas A. Walker, claimed that the appliances for ventilating the tunnel had proved to be thoroughly efficient, the inspecting officer, Colonel F. H. Rich noted that “the means of ventilation are ample, but did not act well when I made my inspection”. Whatever the rights or wrongs, the Guibal fan did not last and was subsequently replaced by a Walker Indestructible fan with a capacity of 27.3 m3/s against 210 Pa fan static pressure. The characteristic curve (Figure 1.28) shows that this was not well-matched to the system and an operating efficiency of less than 40% was achieved. Nevertheless, apart from conversion of the original steam engine drive to electric motor, the unit continued to operate in its original form until very recently. Perhaps the name was well earned after all.
With the steam locomotive as the only proven and practical form of motive power, the idea of a long sub-aqueous railway tunnel raised acute problems of ventilation. Hence the first Mersey rail proposal envisaged pneumatic propulsion, a single carriage, fitting the bore like a piston, being alternatively sucked and blown through the tunnel between terminal air-locks.
This Mersey Pneumatic Railway was authorized by an Act of Parliament June 1866, but it failed to win support so, a more or-
Figure 1.28 Fan characteristic curve for the Guibal fan
Thodox scheme was substituted using condensing locomotives. The name was changed to the Mersey Railway Company and in 1871 it was authorized to make connections with main line railways on both banks and formally opened on the 20th January 1886 by the Prince of Wales.
Despite the use of giant steam-driven ventilating fans of Guibal design, but manufactured by Black Hawthorn, the tunnel had the dubious distinction of possessing the foulest atmosphere of any underground railway. There were two fans 12.2 m diameter x 3.7 m wide and two fans 9.1 m diameter x 3 m wide. It was claimed that the total extract was 274 m3/s. It is interesting to speculate however, that as the fans were effectively in parallel, unless the smaller fans were operating at 33% greater speed, there could well have been a mismatch in pressure characteristics. The tunnel had a ruling gradient of 1 in 27, leading to the locomotives having to work very hard. It is scarcely surprising that as early as 1903 the line was electrified and steam locomotives banished from the tunnel forever.
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