At Zoedale we stock and supply a number of products including: valves, solenoid valves and actuators. One of the less obvious places these products are used is on The London Underground system - We did some research and hope you find this article interesting:

The idea of linking the city by underground railway was first proposed in 1830 to connect the City of London with its main line railway stations. It was granted permission in 1854 and was built and opened in 1863 using steam locomotives pulling gas lit carriages.  On the first day it carried 38,000 passengers and was deemed a huge success. The first deep level ‘tube’ opened in 1890 with a diameter of 10ft 2 and was serviced by electric trains pulling carriages with opaque windows and running on electric lines. The lines are electrified by a 4 rail DC system. All London Underground Lines operate at 630 volts DC using positive and negative current rails. The positive rail is at a potential of 420 volts above earth and the negative rail at 210 volts below earth.

The Metropolitan line was finished in 1863 and was built in the belief that it would be run by smokeless trains with little thought to ventilation. With the lack of ventilation travellers were getting distressed, due to the pollution they were breathing in. In 1887 a Board of Trade report recommended openings in the tunnel to allow the pollution gases to escape but this was a concern to local authorities as they argued that the openings would frighten horses and lower property prices, never the less many more openings were made.

This was also an issue on the Circle Line where forced ventilation was not first considered when it opened in 1900 as it was thought the movement of trains would suffice. Exhaust fans were eventually fitted at most stations but the cooling of the tunnels was not considered until 1938 when a £500,000 programme to improve ventilation was set up. The evaporators consisted of indirect heat exchangers mounted in the platform tunnels which were fed water at just above 0°C. The condenser was situated in the outflow air path of an existing tunnel cooling fan, which had been installed in a disused lift shaft at Tottenham Court Road station. The outgoing air going through the condenser was warmed by 2–3 °C, before being discharged to atmosphere. This was a costly solution and was decommissioned in 1949.

Fans have been used since then to extract the hot air from the tunnels and also as part of the fire prevention and emergency smoke ventilation systems controlled by dampers. Some stations and newer underground trains now also feature air conditioning units making it a much more comfortable experience!

London Underground