Steam Engines

old steam engine copyright the Royal Institution of Cornwall

Steam engines work by using heat to turn a small amount of water into a lot of steam which expands rapidly and powerfully.

If steam condenses, it forms a vacuum which the pressure of the air will try to fill. Steam engines may be divided into four separate types. They are the steam turbine, the atmospheric engine, the separate condenser engine and the compound engine.

Steam Technology - Beam engines

Of the thousands of beam engines erected only a small number have survived and those still on their original sites are fewer still. It must be noted that the relocation of beam engines from one mine to another was very common practice. An engine may have been moved three or four times during its lifetime and therefore may have had several different but entirely authentic locations.

The Steam Turbine

The steam turbine works by squirting out steam like a jet. This pushes against the air and makes the turbine turn. Over 2000 years ago a Greek inventor called Heron made a machine which would spin round. It was a round metal ball which was filled with steam. The steam went out through the jets and spun the ball around. It was not of any practical use but showed that steam could produce power.  In the 19th century Charles Parsons built the first modern steam turbine which used jets of high pressure steam to drive an impellor. It was used to produce electricity and power ships.

 The Atmospheric Engine

The atmospheric engine uses the pressure of the air to work a machine. A piston with a connecting rod moves inside a cylinder. Steam goes into the cylinder under the piston. Cold water cools the cylinder and the steam inside is turned back into water. A vacuum is created under the the cylinder and the pressure of the air pushes the piston down powerfully. The first one which worked effectively was called ‘The Miner’s Friend, invented in 1698 by Thomas Savery. It was used to pump water from mines but needed a lot of coal to operate. It is possible that such an engine was used at Wheal Vor mine, between Penzance and Helston, but the supply of coal must have been a problem. Later, a better atmospheric engine was invented by Thomas Newcomen

The Separate Condenser Engine

The separate condenser engine was developed by James Watt. Look for him in the Information Mine. The atmospheric engine used a lot of fuel. The cylinder was heated up by the steam and then cooled each time the piston moved. This was inefficient and wasteful of fuel. Watt improved the engine by taking the used steam into a condenser outside the cylinder. The steam cooled, turned into water and the cylinder did not have to be reheated. Later, Watt found that he could use steam to push the piston from one side and a vacuum to pull it from the other side. This is called a double acting engine. Watts engines could pump water and also turn large drums to haul materials up deep mineshafts.

 The Compound Engine

The compound engine was the most highly developed form of steam engine. The idea was patented by the Cornish engineer Jonathan Hornblower from Penryn in 1781. He was one of James Watt’s great rivals. When steam at a high pressure was used to drive a piston, there was still some energy left in the steam. The steam was first used in a high pressure cylinder and then again in a low pressure cylinder. They were fully developed in the 19th century and used for the most powerful types of engines such as marine, mill, traction and locomotive engines.

 


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