Triple-expansion engines

The world’s largest working steam engine

The ‘Sir William Prescott’ and ‘Lady Bessie Prescott’ engines are inverted marine-type triple-expansion engines. They were built by Worthington Simpson in Newark-on-Trent and named after the Chairman of the Metropolitan Water Board and his wife. The engines were installed to each pump 12 to 19 million gallons of drinking water per day to reservoirs in North London for the supply of fresh water to The City,  Central, East and West London.

The triple-expansion engines stand 62 feet tall and weigh 800 tons. They have a top speed of 25.4 revolutions per minute and generate 1008 water horsepower.  Each engine has three double-acting cylinders known as the high, intermediate and low-pressure cylinders. Each measures 29, 54 and 86 inches, respectively.  In service days, steam entered the high-pressure cylinder at 200 pounds per square inch. The pressure has been reduced to 60 psi for operation in preservation.  The remaining two cylinders reuse the steam before being exhausted into a separate condenser which produces a vacuum. A bank of Coal Fired Boilers in an adjacent boiler house originally produced the steam. Steam is now generated by a small gas-fired boiler.

The crank webs are set 120 degrees apart, providing smooth, balanced operation to the engine motion and a steady discharge from the pumps into the water mains.  There is no point in the engines’ rotation where no pump delivers water.

The triple-expansion engines were commissioned in 1929 by the Minister of Health, Arthur Greenwood and ceased operating in 1980 when Kempton Park became an electric pumping station.

The ‘Sir William Prescott’  (No. 6) & the Lady Bessie Prescott (No.7) triple-expansion engines are mirror images of one another. 

RMS Titanic’s Triple-Expansion Engines

The triple-expansion engines at Kempton Park are similar in design and size to the engines onboard the RMS Titanic. They are often used in films and documentaries about the ill-fated ship.