The Kempton Park Steam Engines (also known as the Kempton Great Engines) are two large triple-expansion steam engines, dating from 1926–1929, at the Kempton Park waterworks, Middlesex, London. Each engine is of a similar size to that used in RMS Titanic and rated at about 1008 hp. They each pumped 19 million gallons of water a day, to supply north London with drinking water taken from the River Thames. They were the last working survivors when they were finally retired from service in 1980. The engines are of an inverted vertical triple-expansion type, 62 feet (19 m) tall from basement to the top of the valve casings and each weighing over 800 tons. The engines are thought to be the biggest ever built in the UK. One of the engines, called The Sir William Prescott, has been restored to running order and is the largest fully operational triple-expansion steam engine in the world. It may be seen in steam on various weekends during the year.