Cambridge pumping station

Don Unwin’s
CAMBRIDGE OLD SEWAGE PUMPING STATION AND ENGINE

This working model by Don Unwin of the Cambridge Old Sewage Pumping Station and replica pumping engine is one of the great models of the past decade. It is to 1:10 scale and was displayed at the 2015 London Model Engineering Exhibition at Alexandra Palace. The full size engines are approx 36ft long, giving a model of 44in.
The revolution in public hygiene was a response to the cholera epidemics of the early 19th century. It resulted in many advances in civil engineering plus the formation of many engineering companies producing steam engines and related equipment.
In Cambridge, raw sewage was originally discharged directly into the River Cam running through the town making it an open sewer.In 1891 a scheme was devised to improve the condition of the river. That included a pumping station on the river bank to pump the sewage to the treatment works 2 1/4 miles away in the village of Milton. It also included a refuse destructor plant in which the town refuse was incinerated to provide the steam for the machinery.
The station started work in 1894 and continued until it was closed in 1968. The pumping station continues in preservation, the magnificent chimney having been restored in the 1980s by Fred Dibnah.
The pumping engines were made by Hathorn Davey & Co of Leeds. They had tandem 22in. and 44in. dia. cylinders, operating at 80psi. Designed for 80 bhp, they were able to deliver 140ihp comfortably. They discharged 250,000 gallons os sewage an hour, lifting it 50ft.
The engine assembly is mounted on two long bedplate castings (fabricated in the model). The high pressure cylinder, valve bearing castings and compensation wheel castings are bolted to the bedplate. Extension castings carry the low pressure cylinder. The whole bedplate is mounted on a 10ft high brick plinth rising up from a basement. Below the basement is the sump from which the sewage was collected. Above each cylinder are mounted the slide valves, with Mayer valves above them.
Originally both raw sewage and rainwater flowed into the sewers which meant that the depth of fluid in the sump varied widely, affecting the engine load. The engine, therefore, had to be self-governing which led to Davey designing an ingenious Differential Valve Gear, which was to become known as the ‘Steam Man’ (see photo above - foreground).
The Steam man admits steam for longer or shorter periods according to the load. It is fitted with two cylinders, connected to a water-filled cataract cylinder to allow the speed to be regulated.
To make the model Don had only an elevation drawing and a few detail drawings made some years ago. Most of the information for the model came from measurements, photographs, notes and sketches. However, the model was made without formal drawings. Don is reported as saying “I find these quite unnecessary.”
The first item Don made was the Steam Man. No castings were used for any of the components. Fabrications were made using soldering or glueing. Cylinders were made from brass tube. The valve chest cover was made in Perspex so that the action of the Meyer Valve can be seen after removing a decorative cover.
More information about the station is at http://www.museumoftechnology.com/index.html

HP Cylinder

LP cylinder

Sewage pumps

Compensating wheel

‘Steam Man’

Feed pump

Main pump rod

Complete model

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