The No 2 Harvey of Hayle engine was installed as part of the mid-nineteenth century modernisation of Crofton and replaced the original engine installed at Crofton around 1809. The Great Western Railway opened between London and Bristol in 1841 which forced the Canal Company to look for increased efficiencies along the whole length of the canal, including pumping costs. Following the successful rebuild of the No 1 engine as a more efficient Cornish engine, the Kennet & Avon Canal Company ordered a new Sims Patent Combined Cylinder engine from Harvey & Co of Hayle in Cornwall for which even higher efficiency was claimed. The engine cost £1,637.
The No 2 Engine was installed in 1846. However, it proved unsuccessful (although much larger engines of this type worked well elsewhere) and was rebuilt as a conventional single-acting Cornish engine in 1904-5 at a cost of £2,300.
It is also a Single Acting Condensing type with a bore of 1.07 metres (42 inches). The stroke is 2.3 meters (7.7 feet). The Indicated Power is 42 hp (31 kw). The vacuum is -88 kPa (26 inches Hg). Its efficiency is 2.5%.
Unlike the No 1 engine which operates a lift pump, the No 2 engine operates a force pump, the design favoured by Cornish engineers. On the power stroke the heavy plunger is lifted by the engine, drawing water through the foot valve from the pump well. On the return stroke the plunger falls and forces the water through the delivery valve and up the rising main. The valves of this pump are the original double beat valves supplied with the Sims engine by Harvey & Co in 1846.
The No 2 engine pumps water at a rate of 10 strokes per minute, 1154 litres (254 gallons) per stroke.