The 100 inch engine is the largest surviving single cylinder beam engine in the world. Built by Harvey & Co of Hayle in 1869, it first pumped water in 1871. It was one of only six engines of this size built in Cornwall, five of them being built by Harvey & Co. At one time 70% of London's water was pumped by Harvey engines and the company maintained an office at Nine Elms. When running the engine was synchronised with the 90 inch engine so they stroked alternately

Date of manufacture 1869
Cylinder Diameter 100 inches (2.54 metres)
Stroke 132 inches (3.35 metres)
Weight of Beam 54 tons (54.8 tonnes)
Water output per stroke 717 Gallons (3255 litres)
Water output per 24 hours 7.5 M Gallons (34.2 M litres)
Strokes per minute 9 - 12
Last worked 1958
Returned to steam Not yet restored

The engine was in use until the 1940s at which time it was put on stand-by and run occasionally until 1958, when the chimney stack became unsafe and was demolished and the boilers

Interestingly, the engine ran for most of its working life with a cracked beam and the crack and its repair can still be seen today.