Pump in its prime

Of all the great feats of Victorian engineering, one of the greatest is mostly invisible. The sewerage works of London, built in the 1850s under the direction of Joseph Bazalgette, comprise a network of more than 1,000 miles of pipes under the city, incorporating many of the Thames' tributaries.

They not only enabled the city's expansion into the metropolis we know today — Bazalgette carefully calculated the size of piping to meet the demand of the city of the day, then doubled every diameter — they also saved millions of lives, preventing the contamination of drinking water by sewage that had led to devastating cholera epidemics in the East End and Soho. The sewers are the largest part of the network but essential to their operation are four pumping stations at Crossness, south-east London, Erith, Kent, Abbey Mills, east London and Chelsea, where vast steam engines pumped the sewage into holding reservoirs before being released into the Thames.

These pump houses, long superceded by other systems, were marvels of Victorian craftsmanship; the engines were towering constructions of polished iron and brass, set within traceries of wrought iron.

The architectural historian Nikolaus Pevsner called the Crossness pumping station 'a masterpiece of engineering — a Victorian cathedral of ironwork'. But the engines were stilled more than 50 years ago and rust and nature took over.

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The rusted wreck before work began

Step forward the Great British Enthusiast. In the 1980s a group of volunteers decided to try to restore into working order one of the four Crossness pumping engines. The project grew and the Crossness Engines Trust is now restoring the fabric of the pumping house to turn it into a museum of engineering, with two working engines as its centrepiece.

It is no small task. The Crossness Engines — named, patriotically, Victoria, Prince Consort, Albert Edward and Alexandra — are rotative beam engines and the largest of their type surviving in the world. Their flywheels (the rotative part of their operation) weigh 52 tonnes, their beams 47 tonnes. At full power, they could each pump 66 tonnes of sewage every minute.

They were bespoke pieces, built by James Watt & Co to Bazalgette's own design, and entered service in 1865 (covered, of course, by The Engineer). They were upgraded several times during their working lives, being converted into triple-expansion operation, where the steam is expanded three times, each expansion providing force to lift the sewage. They were finally replaced by diesel power in 1913.

The result is four unique engines, mostly unused for almost a century, although Prince Consort was briefly brought back into service in 1953 for marsh drainage.

By 1987, when work began on the restoration project, the engines had rusted almost solid. There was no manual, detailed drawings were not available to the restoration team and no one had any idea how to run them. They were in a leaky, vandalised building, covered with decades of bird droppings.

Where do you start? 'You've got to be truly dedicated, or truly insane, to be able to look at an enormous, rusty, filthy engine and have a long-term view of it,' said industrial archaeologist Peter Skilton, who directed one of the teams that restored Prince Consort, the now fully-functioning engine.

'There are many rotative beam engines about; there are many triple-expansion steam engines. There are even some engines that have the same type of valves as these engines — coreless valve gear. But the combination of rotative, triple expansion, and coreless valves is unheard of. If anyone has heard of another one, could they please let us know?'

Just to make the task even more difficult, the mid-1950s London County Council, in charge when the engines were finally retired, decided to infill a large part of the basement of the pumping house with sand and cement for safety reasons. 'All of that had to be dug out before we even started,' said Skilton.

Skilton is not an engineer — his expertise is in the historical aspects of the machinery of the Industrial Revolution and its subsequent years. However, each of the teams working on various sub-systems of the engine included retired engineers.

'We had one man who'd worked as a machinist at the Royal Woolwich Arsenal and another, who is now well into his eighties, had spent his entire working life as an engineer. I learned a great deal from them,' said Skilton.

With the massive task facing them, the trust decided that the best way to tackle Prince Consort was to strip it down, clean all the parts, then reassemble them — something like doing a giant, three-dimensional jigsaw without a picture on the box. 'We decided that we'd bring the engine back to the condition it was in 20 years before its demise. We wanted to use as much of the original material as possible, so we had to get rid of a lot of rust and in some cases some deep pitting in the ironwork.'

This meant that nearly all the work was done without recourse to modern engineering methods. 'My team was working on part of the water pump in the condensing area, which we just could not repair, but we had to at least be able to show how it had worked.

'We had great trouble separating one part from another; we worked on it for three months — we only work two days a week — and eventually our elderly team member said we'd have to trepan it out. I thought that meant cutting holes in people's heads, but he called me an idiot and explained it was a way of cutting metal, and sketched out the machine we'd need to do it, almost literally on the back of an envelope.

'We got this machine built, which had a windlass on it so we could turn the cutting tools, and four of us turned the windlass while singing sea shanties. It attracted some attention, but it worked; we've preserved the original sketch of the tool in our display.'

Removing rust proved problematic. 'The high-pressure and intermediate-pressure cylinders are in tandem, which means that the piston rod goes through both cylinders, and it's about 30ft long and 4in thick. We had access to a machine shop with some pretty heavy gear in it, but there wasn't a lathe big enough for this rod. We had to put it out to tender. Then we had a learning curve — when you lay a rod like that on its side, you have to be very careful to avoid sagging and warping under its own weight.'

Despite that, Skilton said 'virtually nothing was refabricated' — the largest non-original components were steam sealing glands in the cylinder heads and some small parts of the valve gear.

Once each component had been recovered or repaired they were hand-finished and polished, just as in the 19th century. 'Everything shone like regimental silver,' Skilton said.

Once the engine was reassembled, getting it working was the next challenge. 'We had yet another steep learning curve on how this type of engine operates and all the intricacies of the timing system for the valves because, of course, nobody knows how to run it. We seriously considered going to the pump engine museum at Kew Bridge [in west London] cap-in-hand and asking how they'd managed to operate their big engine, but their engine isn't a rotative beam so they couldn't have helped anyway!'

The team has now started work on another engine, Victoria, although there are no plans to restore the other two; they will be mothballed and left to show visitors a before-and-after view. 'When we finished Prince Consort, our chairman, Peter Bazalgette, wanted to carry on. We asked our volunteers what they thought, and we got an answer back in typical engineering terms: we're not going to touch another engine like that, find another idiot. And fortunately, we found another idiot.'

A £1.5m grant from the Heritage Lottery Fund is now going towards making the building watertight, which has curtailed work on Victoria and the running of Prince Albert. But Skilton is sure that in time the magnificent cathedral of iron and steam will again ring with the gasp and creak of the engines that helped keep London alive.