The Crossness Pumping Station is a former sewage pumping station designed by the Metropolitan Board of Works's chief engineer Sir Joseph Bazalgette and architect Charles Henry Driver at the eastern end of the Southern Outfall Sewer and the Ridgeway path in the London Borough of Bexley. Constructed between 1859 and 1865 by William Webster, as part of Bazalgette's redevelopment of the London sewerage system, it features spectacular ornamental cast ironwork, that Nikolaus Pevsner described as "a masterpiece of engineering – a Victorian cathedral of ironwork". It is adjacent to Erith Marshes, a grazing marsh, the northern part of which is designated as Crossness Nature Reserve. This provides a valuable habitat for creatures ranging from moths to small amphibians and water voles.
At 11 revolutions per minute, 6 tons (approximately 1,500 imp gal or 6,800 l) of sewage per stroke per engine were pumped up into a 27-million-imperial-gallon (120,000 m3) reservoir, and was released into the Thames during the ebbing tide. The steam required to power these engines was raised by 12 Cornish boilers with single "straight-through" flues situated in the Boiler House to the south of the Engine House, and which consumed 5,000 tons of Welsh coal annually.
The Crossness Works merely disposed of raw sewage into the river seawards, and in 1882, a Royal Commission recommended that the solid matter in the sewage should be separated out, and that only the liquid portion remaining should be allowed, as a temporary measure, to pass into the river. In 1891, sedimentation tanks were added to the works, and the sludge was carried by steam boats and dumped further out into the estuary, at sea.
By 1897, additional pumping capacity was needed, and four extra pumps operated by triple-expansion steam engines were installed in an extension, designed to fit in with Bazalgette's main engine house, to the north of the older building. Later, in 1899, a further increase in London's population necessitated an increase in the efficiency of the original Watt engines, and considerable alteration to their design was carried out by Goodfellow and Co of Hyde, Manchester, for London County Council. They were converted from simple to compound engines with the original single cylinders were augmented by high and intermediate pressure cylinders. The additional steam required was provided by replacing the earlier Cornish boilers by more efficient Lancashire boilers with double flues and in 1901 the improved engines were fully working.
In 1913, the triple expansion steam engines were replaced by diesel engines, which are still to be seen in the triple expansion engine house, and by 1956, the Watt-Goodfellow engines had been decommissioned, (Prince Consort having been temporarily put back in steam in 1953 to assist with draining the flooding of the eastern Royal Arsenal and Abbey Wood) and were left, with the rest of the ironwork, to rust and to vandals.
The pumping station became a Grade I listed building in 1970 and will remain on the Heritage at Risk Register until the restoration is completed. The Crossness Engines Trust, a registered charity, was formed in 1987 to oversee the restoration project. When the pumping station was decommissioned in the 1950s, it was not considered economic to dismantle the engines, as the cost of doing so far exceeded any scrap value. The more valuable metal items (made from brass), such as the engine oilers, much pipework, and even the handrails from the stairs, were removed. The remaining building and engines were left to suffer considerable vandalism and decay.
When the buildings were abandoned, the pumps and culverts and all the subterranean areas below the Beam Engine House were filled with sand to reduce the risks from methane. This has meant that some 100 tons of this sand has had to be excavated from around and underneath the pumps before there was any hope of moving the beam and flywheel. Further, there was a considerable ingress of rain water which resulted in serious rusting of the engine parts.
The station contains the four original pumping engines, which are thought to be the largest remaining rotative beam engines in the world, with 52-ton flywheels and 47-ton beams. Although the engines are original, they are not in their original 1864 configuration, as all four were converted from single-cylinder to triple-expansion operation in 1901 and 1902. Prince Consort was returned to steam in 2003 and now runs on Trust Open Days. The other engines are not in working order, although work has begun on the restoration of Victoria.
Having received over £2 million in initial funding, including, in 2008, £1.5 million from the Heritage Lottery Fund, £150,000 from English Heritage and £700,000 in match funding from the Department for Communities and Local Government, work began at the site to build an access road, protect the buildings and to develop a museum. Financial and other support was also provided by Thames Water, Tilfen Land, the London Borough of Bexley and the City Bridge Trust. A further £1.5 million in funding from the Heritage Lottery Fund was secured in April 2015, the 150th anniversary of Crossness's official opening. This was to help fund a museum exhibition focused on the "Great Stink" of 1858 and the role of Crossness in improving London's sewerage system.