The power and the glory of museum's Shropshire jewel

And what's more, despite being 86 years old, it's still working, a thing of wonder to the thousands of visitors a year who flood through the doors of the museum near Maldon in Essex.

The Marshall is a rare survivor, and is believed to have been the last steam engine ever built by the Lilleshall Company at Oakengates.

Like many a mechanical marvel, it has its little quirks of personality.

"It's very well behaved, but needs a little TLC occasionally," says Ray Anderton, who leads the team which looks after this fine example of an inverted vertical triple expansion steam pumping engine. It was one of three identical Lilleshall Company-built engines installed at the site, a former waterworks supplying treated drinking water to Southend, but the only one to have avoided being scrapped.

"At times, it develops a mind of its own and you wonder why. If you look back in the history, each engine had its own characteristics. Marshall would always run away on start, irrespective of how you started it. You had two guys hanging on to the governor to slow it down, and then it would run for eight months as happily as can be.

"It does pick up speed quite quickly. It runs at 30rpm.

"It's very quiet. We have spoken to people who worked with it before the end of steam working in 1963, and they said it was a nightmare staying awake at nights. One gentleman told us that he used to keep a spanner between his knees so that if he dozed off the spanner would clatter on the floor."

Langford waterworks officially opened in September 1929 with two engines made by the Lilleshall Company. Marshall was not installed then, becoming the third and last to be commissioned, on January 13, 1931.

After decades of operation faithfully pumping water for the Southend area, the Langford pumping station could no longer keep up with demand.

The works switched to electric pumps, turning off its steam pumps in October 1963 and then in 1970 a new modern waterworks was completed, and the original works seemed destined to fall into decay.

Salvation came in 1996 when the go-ahead was given to a group of enthusiasts to turn the original building into a new museum - the Museum of Power - with the Shropshire-built engine still in situ as its centrepiece.

With two of the Shropshire-built pumps being scrapped - their scrap value was about £1,200 - it was down to the determination of one man that the third, Marshall, did not go the same way.

"There was a director of the water company who wanted the last engine saved and he fought tooth and nail. Finally he got approval to keep it, and the whole building was mothballed. His name was Percy Gordon Spencer, chief engineer of the Southend Waterworks Company. He was pretty near to retirement and it was his final wish to the company to save it."

Restoration began in 2007.

"The major problem was that the pump sets are in a basement six metres deep. That basement is below the water table. You can imagine it was in a pretty sorry state down there."

The original boiler had been scrapped at roughly the same time as the other two steam engines had been, and had to be replaced. Among other major issues was that it had asbestos lagging, and parts were missing from the lubrication system.

Budget for the restoration was £45,000, and it came in just under, at £44,700. The dream was triumphantly realised in April 2011 when the engine was restored to power, nearly 50 years after it was last worked.

Ray began to get involved in 2008, and now heads the team which runs and maintains the engine, which is run on special events days during the year.

"It's fully functioning," said Ray.

"The only thing we don't do is pump water. We can run at operational speed on steam or compressed air. We have eight to 10 steam events throughout the year."

As for the name Marshall, the three Lilleshall Company engines installed all those years ago were named after directors of the Southend Waterworks Company. Marshall was named after the deputy chairman, J. Maitland Marshall. The other two were named Francis, after chairman Joseph Francis, and Brassey, after Sir Leonard Brassey.

As well as being a living part of Shropshire industrial history, albeit far from "home," the Lilleshall Company's masterpiece also has a place in national industrial history.

"We believe it's the only one in the UK in its original location and with its original pump sets," said Ray.

For the technically minded, the engine has three cylinders, with bores of 20 inches (508 mm) diameter (high pressure), 35 inches (889 mm) diameter (intermediate pressure) and 56 inches (1,422 mm) diameter (low pressure). The stroke is 42 inches (1,067 mm). Each piston rod is 5 inches (127 mm) diameter. It is rated at 350 horsepower.

In original operation two of the three engines were always running, while the third was in maintenance or repair, giving a combined pumping rate of about eight million gallons of water a day, depending on demand.

Today the engine continues proudly to declare its Shropshire heritage - amid the gleaming dials and brasswork on the control panel it declares: "Lilleshall Co Ltd, Oakengates, Shropshire. Engine 282."