How did the Engine Rooms work?

Nowadays, the Tower Bridge bascules raise and lower via electricity. However, before 1976, the process was powered by water and steam.

This steam and hydraulic system was a marvel of Victorian engineering, allowing Tower Bridge to open for ships passing through to the Pool of London.

The process

The Boilers

The process began with the boilers, where coal fires heated water to produce steam.
The boiler room was extremely hot and needed workers to constantly feed coal and top up the water.
Gauges measured the energy levels. If it got too high, they risked explosion.

The Steam Pumping Engines

Steam moved to the steam pumping engines, where it powered a flywheel and pistons.
The pistons converted steam energy into mechanical motion.
The beautiful green colour of the flywheels were personalised by the engineer William Armstrong, reflecting his family crest.

The Pistons and Hydraulics

The pistons powered water pumps, creating high-pressure water (hydraulics).
This pressurised water was then collected in a tank called an accumulator.

The Accumulators

The accumulators stored the pressurised water like a battery stores electricity.
They were raised high to maintain energy, and when released, they sent water to power the Bridge.

The Cog

Pressurised water drove the cog, which rotated to open or close the Bridge via teeth that fit into the Bridge's mechanism.

1976: The Big Switch

Tower Bridge switched to electricity in 1976, replacing its original steam-powered hydraulic system.

The transition began in 1974, driven by a desire to improve the efficiency of bridge lifts and reduce fossil fuel emissions.

The new electro-hydraulic system to operate the bascules offered a more modern and environmentally friendly alternative while maintaining the Bridge’s historic structure.

Perfect for Educators

Keep those cogs turning!

Did you know, your class can put their Engine Rooms expertise into practice with our fun, interactive Engine Rooms Challenge: can you fix the Bridge in time for the approaching ship?

This is a free online session - perfect for Key Stage 1 and 2.

Engine Rooms Challenge

Get your mental gears grinding with our fun worksheet which explores the vital role cogs play in raising Tower Bridge!

Download worksheet