Beam engine

A beam engine is a design of engine based on the principles of a first-class lever. A force is applied to one end of a beam, which is pivoted in the middle, and the lever action transfers the force to create work at the other end of the beam.

The most familiar example is the type of stationary steam engine used for pumping water from mines. Here the piston of a vertically-mounted cylinder is attached to one end of the beam, to apply the force through upward and/or downward motion. The other end of the beam is connected to a vertically-acting pump. A downward pull on the piston causes the other end of the beam to lift whatever is attached to it, thereby doing 'work'.

The most common engine was the stationary steam-driven type, but water, wind or other forms of propulsion could be used.

Beam engines need not be 'stationary'. The steamboat Eureka is still powered by its rotative beam engine.



History

The first beam engines were water-powered, and used to pump water from mines. A 'preserved' example may be seen at Wanlockhead, in Scotland.

Beam engines were extensively used to power pumps on the English canal system when it was expanded by means of locks early in the Industrial Revolution, and also to drain water from mines in the same period, and as winding engines.

The first steam-powered beam engine was developed by Thomas Newcomen. The Newcomen steam engine was adopted by many mines in Cornwall and elsewhere, but it was relatively inefficient and consumed a large quantity of fuel. James Watt resolved the main inefficiencies of the Newcomen engine in his Watt steam engine, and these beam engines were used commercially in much larger numbers.

Watt held patents on key aspects of his engine's design, and it was not until these patents expired that others could develop modifications to improve it. The beam engine was considerably improved and enlarged in the tin- and copper-rich areas of south west England, which enabled the draining of the deep mines that existed there. Consequently the Cornish beam engines became world famous, as they remain the most massive beam engines ever constructed.

Rotative beam engines

In a rotative beam engine, the piston is mounted vertically, and the piston rod does not connect directly to the connecting rod, but instead to a rocker or beam above both the piston and flywheel. The beam is pivoted in the middle, with the cylinder on one side and the flywheel, which incorporates the crank, on the other. The connecting rod connects to the opposite end of the beam to the piston rod, and then to the flywheel.

Early Watt engines used Watt's patent sun and planet gear, rather than a simple crank, as use of the latter was protected by a patent owned by someone else. Once the patent had expired, the simple crank was employed universally.

Compounding

Compounding involves two or more cylinders; waste low-pressure steam from the first, high-pressure, cylinder is passed to the second cylinder where it expands further and provides more drive. This is the compound effect; the waste steam from this can produce further work if it is then passed into a condenser in the normal way. The first experiment with compounding was conducted by Jonathan Hornblower, who took out a patent in 1781. His first engine was installed at Tincroft Mine, Cornwall. It had two cylinders – one 21-inch (0.53 m) diameter with 6-foot (1.8 m) stroke and one 27-inch (0.69 m) diameter with 8-foot (2.4 m) stroke – placed alongside each other at one end of the beam. The early engines showed little performance gain: the steam pressure was too low, interconnecting pipes were of small diameter and the condenser ineffective.

At this time the laws of thermodynamics were not adequately understood, particularly the concept of absolute zero. Engineers such as Arthur Woolf were trying to tackle an engineering problem with an imperfect understanding of the physics. In particular, their valve gear was cutting-in at the wrong position in the stroke, not allowing for expansive working in the cylinder. Successful Woolf compound engines were produced in 1814, for the Wheal Abraham copper mine and the Wheal Vor tin mine.Here, the cut-off problem had been solved but the engines were compromised by being single-acting: both cylinders driving the same shaft. This action was improved by Galloways of Manchester, whose horizontal side-by-side compound arrangement was patented in 1873.

McNaught engines



William McNaught of Glasgow, not to be confused with William McNaught of Rochdale (Petrie and McNaught), patented a compound beam engine in 1845. On a beam engine of the standard Boulton & Watt design he placed a high-pressure cylinder, on the opposite side of the beam to the existing single cylinder, where the water pump was normally fitted. This had two important effects: it massively reduced the pressure on the beam, and the connecting steam pipe, being long, acted as an expansive receiver – the element missing in the Woolf design. This modification could be made retrospectively, and engines so modified were said to be "McNaughted". The advantages of a compound engine were not significant at pressures under 60psi, but showed at over 100psi.

From http://en.wikipedia.org/