The Thomas Horn Engine at the Bredgar & Wormshill Light Railway

A major manufacturer of beam engines was Thomas Horn of Westminster and in 1870 he built and supplied two beam engines of the James Watt design for the Water Company at Ashford, Kent.
These rotative steam engines were decorative as well as utilitarian and had fluted Doric columns and polished steel motion. They each operated a three cylinder pump which lifted water from a well and delivered this to a reservoir from which it was distributed to premises throughout the Ashford area.
The engines worked from 1870 to about 1940, at which time a new pumping house was erected and new electrically powered pumps installed. The site on which the engines worked at Henwood was required for other purposes and in 1998 Mid-Kent Water made one engine available to the Bredgar & Wormshill Light Railway which is situated about 25 miles from Henwood.
This wonderful example of Victorian engineering has been restored at Bredgar and has been erected in a way which resembles the original installation, insofar as this is possible. The pumps are about three metres below ground level, as they were originally and the engine drives the pumps through a mechanism which can be closely observed. The steam is supplied from a modern boiler in an adjacent building.
The engine can be seen in steam on the regular Open Days at the railway, which are held on the first Sunday in each month from May to September. It is also possible for members of the public to see this engine on other weekends by appointment.

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Technical Details

Engine type:

Woolf compound single column rotative beam engine

Builder:

Thomas Horn, Westminster, London. 1870

Cylinders:

High Pressure 8 inch x 25 inch

Low Pressure 14 inch x 27 inch

Slide valves

Watt - type governor

Single plate cast-iron beam

Forged connecting rod

Three throw well pump

Gear drive with hardwood teeth

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Method of Operation

Steam is delivered at 30 pounds per square inch to the high pressure cylinder. At the end of the stroke it is exhausted into the low pressure cylinder at a pressure of 8 pounds per square inch. The steam leaves the low pressure cylinder via a combined air pump and jet condenser. By condensing the exhaust steam a vacuum is created in the low pressure cylinder, thus increasing the power.
The two pistons are connected to the beam by a complicated formation of rods known as a parallel linkage which, as a consequence of careful geometric design, transmit power in an exact vertical line. The beam then rocks and a rod at the other end of the beam which is connected to the large flywheel causes this to rotate. A wooden toothed gear wheel is driven from the main flywheel and this rotates a crankshaft which has three rods each attached to a water pump.
The speed of the engine is kept constant by the automatic pendulum governor, which has two heavy metal spherical weights which move under centrifugal force and open and close the main steam valve. The condensor and air pump can be seen below and just to the left of the Doric column supporting the beam. Originally steam for this engine would have been generated from a coal fired boiler. The only concession to up-to-date technology is that steam is now produced by a modern oil fired automatic boiler.
Click here to see how a simple beam engine works.

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The Development of Beam Engines

The supply of mains water, which we now all take for granted, has only been available to every factory and house in the U.K. for perhaps the last eighty years, although parish pumps and taps serving several households were in general use for many years before.
In the period prior to 1850 water for almost every application was drawn from thousands of private wells, streams and rivers and, until the discovery of the power of steam, windmills and watermills provided the bulk of power for industry. The only other power available was horsepower and manpower, both extremely limited in so far as the supply of water was concerned.
The lack of mechanical power was a major difficulty to be overcome in the need to provide a plentiful supply of clean water to private users and industry. However a problem regarded as more pressing than this was the need to find a method of pumping ground water from mines, especially coal mines. In the eighteenth century coal was in great demand, for this was the beginning of the Industrial Revolution.
The answer came from an unlikely source, an ironmonger and brassfounder from Devon, Thomas Newcomen (1663 - 1729). He recognised the power in steam, but it was quite impossible to use steam under pressure for no metal technology existed to make suitable boilers. It is said that for about fifteen years Thomas Newcomen experimented with many engine designs, but eventually he erected a large wooden beam, pivoted on a large strong wall. To a chain attached to one end of the beam he attached the piston of the engine (situated within a cylinder). A chain at the other end of the beam was attached to a rod connected to a pump at the bottom of the mineshaft. By alternately filling the bottom of the cylinder with steam and condensing this with water, a vacuum pulled the piston down with considerable force and operated the water pump.
The first engine erected by Newcomen in 1712 pumped water from a mine at Dudley Castle. A replica of such an engine may be seen at the Black Country Museum at Dudley. Many such engines worked well for over one hundred years, but their use was limited to areas where there was a plentiful supply of cheap coal, for the engines were very inefficient in their use of fuel. This primitive engine was the forerunner of many other better designs.
In 1720 as in 2000 fuel economy was of paramount importance. John Smeaton (1724 - 1794) was an engineer who greatly improved the design of beam engines and his engines were used to pump domestic water from the Thames. However it was a Mr James Watt (1736 - 1819) who invented improvements which transformed the beam engine. In 1769 he patented a device for condensing the steam outside rather than inside the cylinder and in 1775 began to manufacture engines for which the demand was enormous.
A great handicap in the design of engines at this date was that they did not provide rotary motion but Watt and others found a solution by about 1780, and the rotative beam engine became available. Boiler design was also improving and steam, albeit under very low pressure, became available, further improving the engines. Many built around 1790 worked well for periods in excess of fifty years.
By 1800 Watt had built no less than 450 engines and, during the following fifty years, improvements were made at an accelerating rate with engines even being adapted for marine use. The most important improvements resulted from metallurgy technology and the ability of engineers to construct boilers which could provide high pressure steam. This development also resulted in the first steam railway locomotive being constructed soon after 1800.
The availability of steam at a pressure of 50 pounds per square inch enabled an Arther Woolf (1776 - 1837) to invent compounding which, in effect, allows steam to be used twice, first in a high pressure cylinder and then in a low pressure cylinder, both being connected to the same beam. The exhausted steam is then condensed in a separate condenser. These improvements resulted in enormous economy of fuel and greatly increased power output.
It should be understood that electrical power was not available at this time and so these compound rotative beam engines were in enormous demand for factories, mines and mills throughout the U.K., Europe and the U.S.A. They were built until about 1900 and some were still working until 1960. By 1840, the design of beam engines had probably reached a peak and many manufacturers were building engines which ranged from the very large to the very small. The former could have flywheels weighing more than 60 tons and were capable of pumping vast quantities of liquid.
A great engine at Kew Bridge Water Pumping Station, London is the largest in the U.K. It worked from 1871 to 1944 and lifted ten million gallons (forty five million litres) of water every twenty four hours. One of the London sewage pumping stations at Crossness has four enormous James Watt engines on site. Built in 1864 these engines are undergoing restoration. Although spectacular, large engines such as these were relatively unusual for most factories required small power units. The flywheels of such engines could be as small as three feet (one metre) in diameter and weigh as little as one ton. Again examples are preserved in museums throughout the country and, in particular, at the science museum in London. The engines at Kew Bridge and those at many other sites in Britain are fully restored and some may be seen at work on the Open Days arranged by site owners.