This is one of the two Hathorn Davey pumping engines installed in 1894 to pump the sewage from the well beneath the engines to the treatment plant at Milton. These are the only engines of this type still running in the world.
Each engine itself consists of two cylinders in tandem, high pressure and low pressure, driving a rocking disc. This disc acts as a ninety degree bell crank converting the horizontal motion of the engine into the vertical motion of the pump rods. There are two pump rods which drive the bucket of each pump in turn.
These steam engines pumped the sewage from Cambridge through underground pipes to the sewage farm at Milton, 2 miles away (2km). As the town grew in size and more roads and pavements were drained into the sewage system the original pumps could no longer cope with the volume of fluid in a heavy rainfall.
This mixture of water and other objects was used to cool the condensers of the steam engine and when the condensers were cleaned some of the pipes were often found blocked by scrubbing brushes or similar objects. The condenser air-pump is driven from an arm on the end of the flywheel shaft through two vertical rods.
Also in the Main Engine house there is a number of other steam engines including a Mumford engine used to pump feed water back into the boiler and a Crompton and Parkinson engine which was used to generate electricity to power lights in the pumping station and the engineer's house.