British Steam Engine Recognized As First Boulton and Watt with Parallel Motion

During ceremonies on April 17, Dr. L. S. Fletcher, president of the
Society, presented a bronze plaque to Dr. Lindsay Sharp, director
of the Power House Museum, part of the Sydney Museum of Applied
Arts and Sciences, in Australia.

The parallel motion mechanism is the critical element that
allowed long-stroke pumping engines to become double-action and
thus able to produce rotational motion. Built in 1785 as a
single-acting engine, the Boulton and Watt was altered to its
present double-acting configuration in 1795.

Museum staff Bill Bannister and Bert Bruin check parts near the
14-foot flywheel of the Boulton and Watt steam engine now in the
Museum of Applied Arts and Sciences in Sydney, Australia. Photo
courtesy of ASME and the Museum.

Replaced in 1887 by a more compact, higher powered compound
steam engine, it was donated to the Museum and shipped to
Australia, where it has been on display since 1888. It was once
again restored to working condition for its bicentennial last
year.

The engine was high technology for its day and more imposing
than other mechanical achievements of the time the windmill and the
clock. In May of 1797, King George III took Queen Charlotte and
their children to inspect the Brewery works, the chief attraction
being the engine. Although of modest capacity, it set a good
example, and by 1796, 11 other Boulton and Watt engines were at
work in London.

With the ever increasing industrial activity of the 18th
century, rotational power beyond that derived from animals, water,
or wind was desperately needed. New comen atmospheric pumping
engines were used for mine drainage and water systems, but the high
cost of fuel was limiting. Millwork was dependent upon shaft power,
but these engines had inadequate drives. The unlimited industrial
application of a rotative engine was recognized by James Watt, an
engineer who in 1776 began a partnership with industrialist Matthew
Boulton.

The mechanical invention of which Watt was eventually to say he
was proudest is the three-bar mechanism. Watt patented his first
parallel motion mechanism in 1784, about the time that Samuel
Whitbread, a London brewer, had ordered a single-acting, 24-inch
cylinder, 6-foot stroke engine. Whitbread’s engine was to be
rotative, and a drawing (in the Boulton and Watt Collection in
Birmingham) dated November 1784 shows a parallel motion, believed
to be the first application of that mechanism. The engine is shown
laid out with rack and sector hookup, but a three-bar motion was
sketched over it. The Whitbread drawing of a few months later shows
a refined parallel motion.

The Brewery’s engine is 30-feet (9.14 m) tall and has about
the same length, with an overall weight of 33 tonnes. Sometime
after the 1795 rebuilding, a cast iron beam, 18 feet 4 inches (5.6
m) center to center and weighing about 9.2 tonnes, replaced a wood,
probably oak, beam that might have weighed about 1.5 tonnes. Built
of cast iron sections, the 14-foot flywheel and its shaft weigh
some 8 tonnes. The connecting rod is 18 feet (5.5 m) center to
center.

When first installed in London, the single-acting engine did the
work of 24 horses, according to records. This probably meant the
total number of animals required during a day not a shift, since a
conservative calculation leads to about 17 indicated horsepower
(12.7 kW) assuming a mean effective pressure of 10 psia (69 kPa)
and a speed of 20-21 strokes per minute. After the engine was made
double-acting in 1795, the power of its cylinder doubled, to an hip
of perhaps 35 (26 kW).

The ASME National Historic Mechanical Engineering Landmarks
Program designates regional, national, and international landmarks,
each representing a progressive step in the evolution of mechanical
engineering. Each is judged by its influence on society and
significance in its immediate locale, in the country, or throughout
the world. To date, 112 such landmarks have been designated in 29
U.S. states, Puerto Rico, England, France, and now Australia.