The 1904 engine was one of the last waterworks beam engines ever built, and as such may be seen as representing the pinnacle of beam engine pumping development. It is a rotative, two-cylinder Woolf compound engine, designed by Glenfield and Kennedy of Kilmarnock and built by Teasdale Bros, under T&C Hawksley, Civil Engineers, London. The beam is just over 30 feet (9.1 m) long, weighing 25 tons; the flywheel is 21 feet (6.4 m) in diameter, and the high- and low-pressure cylinders measure 18" and 29" respectively (46 cm and 74 cm). It is housed in a building erected for an earlier beam engine in 1849. The engine ran almost continuously from 1904 to 1926, when new electric pumps were commissioned; thereafter it remained on operational standby until the mid-1950s, and continued to be run one day each year, on the order of the Borough Engineer, until at least 1968.

The 1914 engine is by Richard Hornsby & Sons of Grantham, with pumps by Hawthorn, Davey & Co. of Leeds, all housed in a building of 1853 which previously accommodated an earlier steam engine. It presently runs on mains gas, but originally used producer gas from an adjacent plant on site. The producer plant is still in situ and open to the public; however it suffered at least two explosions over the years, evidence of which is still clearly visible, and it is no longer operational.

The steam and gas engines were superseded by a set of electrically powered centrifugal pumps installed in 1926 and which ran until 1980. These too remain in situ and are on public view. A machine tool workshop has survived, complete with the belt-driven line shafting, as has the on-site blacksmith's forge, which is often fired up and demonstrated on open days. Three of the four original filter ponds are also extant. The original Superintendent's house now houses a tea-room for visitors.

Tees Cottage Pumping Station was closed in 1980, and placed in the care of a Preservation Trust. (The site is still owned by Northumbrian Water, which continues to supply Darlington from its Broken Scar works, just across the A67 road from Tees Cottage). Tees Cottage is one of 2 sites in Britain (the other being Kew Bridge) which shows all 3 forms of water pumping (steam, internal combustion, electric). The significance of the site is summarised thus by H C Devonshire:

"Tees Cottage really is unique. An analysis of 115 other sites in England, Scotland and Wales ... shows that while 50% of them have one or more engines in steam, very few are on their original site and using their original boilers, and only one on the listing, a gasworks exhauster engine in Scotland, can still do its original duty. Given that Tees Cottage also has what is believed to be the largest working preserved gas engine in Europe and still has all the electric pumps and switch gear from 1926, and still pumps water as intended, this station is a very rare opportunity for future generations to study not only the total history of water pumping and engines but also the totality of life in the Victorian and Edwardian era in a complete and original context".^[1]

• Ryhope Engines Museum for another working example of preserved waterworks beam engines in County Durham.

• Tees Cottage Pumping Station website
• Video of the beam engine, gas engine, and workshop line shafting in operation (with captions)

54°31′13″N 1°36′21″W / 54.52034°N 1.60582°W / 54.52034; -1.60582