Opened in 1894, Tower Bridge was a masterpiece of Victorian mechanical engineering, designed to resolve a critical urban crisis: allowing river traffic to reach the busy Upper Pool of London without halting horse-drawn road traffic indefinitely. To lift the bridge's two massive 1,000-ton bascules in under one minute, engineers Sir John Wolfe Barry and Sir William Arrol designed an ingenious high-pressure hydraulic system powered entirely by steam and water. At the heart of the system sat two 360-horsepower coal-fired horizontal compound steam engines pumping filtered water from the Thames into huge hydraulic accumulators at a pressure of 700 pounds per square inch.
These accumulators featured massive 100-ton weighted rams suspended inside steel towers. When water was pumped beneath the rams, they rose, storing vast amounts of potential energy. When a ship approached, high-pressure water was released from the accumulators into hydraulic drive motors equipped with pinion gears.
These gears engaged large circular racks attached to the heels of the bascules, effortlessly swinging the giant counterbalanced arms upward in just 80 seconds. The system was so redundant and efficient that it operated reliably for eighty years until it was converted to electro-hydraulic operation in 1974. Today, the original coal boilers, steam pumps, and massive cast-iron accumulator cylinders remain preserved in the bridge engine rooms as a monument to Victorian power.