Sovereign Hill Cornish Bob-Pump

Background

The world’s first steam engines were built during the reign of Queen Anne (1702-14), in response to a need to drive pumps to keep mines free from water, so that rich sources of coal and ore could be mined. Those first ‘fire engines’ were built by Thomas Newcomen, and the design was improved over the next 60 years by John Smeaton, and then James Watt. The mine pumping engines were adapted for pumping domestic water supplies and emptying dry docks, and in Watt’s time were first applied as industrial engines in non-pumping duties. The Watt design of separate condenser beam engine continued to be important in mine dewatering until the end of the 19th century, by which time it had become popularly known as the Cornish engine.

One of the main industrial areas of England was Cornwall, where there was an unprecedented demand for tin and copper as well as tungsten and various other metals. Lead was being worked everywhere, in southern Scotland and in every county of Wales. New coal-mines were continually being sunk; all these holes in the ground needed to be kept free of the water which poured into them from the subsoil. Firms were established in many industrial areas to manufacture beam pumping engines, but most of all in Cornwall, where enormous foundries turned out at short notice steam engines, boilers, pumping equipment and pitwork of every possible description. Largest of all was Harvey’s of Hayle, also the Perran Foundry, and the Copperhouse Foundry.

Australia and Ballarat

In Australia, as in Britain and elsewhere, industrial technology followed the need for mine dewatering. Developments in mining in South Australia during the 1840s led to the importation of beam engines and the rise of a local foundry and engineering industry.

A similar situation arose in Victoria, with sudden industrial development occurring in Melbourne and in provincial centres following the rise of the gold-mining industry. In shallow gold mining, shafts were bailed out with rawhide buckets or iron 'kibbles'. Shaft-sinking contracts usually included a clause terminating the contract at an agreed depth or inflow rate of water. Deep mines in some areas were able to keep down the water using bailing tanks alone, which was the practice at the Central Deborah Mine, Bendigo, until it closed in 1954.

The first steam pump on the Victorian goldfields was installed on the Gravel Pits Lead, Ballarat, in 1854. Some of the miners took a Luddite view of the use of machinery. Wood (1869) records that 'a body of men proceeded to the claim for the purpose of smashing the engine, but were prevented from doing so by Mr Talbot ... who had provided himself with firearms, and threatened to shoot the first man who approached'. Until the late 19th century, all mine pumps employed Cornish pitwork. This comprised a strong timber rod which moved up and down in a compartment of the mine shaft, transmitting the power of an engine on the surface to the pumps at various levels of the mine. A draw-lift or 'suction' pump worked in the shaft-well or sump at the bottom of the mine. Water from the draw lift supplied the main force-pumps through a header tank. In deep mines several stages of pumps at locations up the shaft acted off the one pump rod. The rods were typically 12 inch square oregon, but could be larger. On the few Victorian mines where water became a serious problem, Cornish condensing engines were used. The building housing such an engine was an integral part of the engine itself, and massive and expensive construction was required.

The majority of Victorian mines used a simpler and less expensive above-ground installation. This was a horizontal rotative steam engine driving a crank-arm through reduction gears, with a large balance-bob set in a pit beside the shaft collar. While archaeological reports are available on Cornish engine sites nothing seems to have been published on the horizontal-engined bob pumps.

How it works

The beam pump is capable of pumping water from mines of depths in excess of 1000 metres. It consists of a horizontal reciprocating steam engine driving a heavy crank through direct reduction gearing. The crank imparts a reciprocating motion to a horizontal arm at about 10 strokes per minute, and the horizontal motion in the arm is converted to vertical motion by use of a balanced rocking beam, situated at the edge of the mine shaft. A string of square wooden pump rods is suspended from the end of the rocking beam, and is constrained laterally by timber guides fixed at intervals down the shaft. The reciprocating action of the pump rods acts on a simple plunger pump which is located at the bottom of the shaft in a water sump. The water is displaced by the plunger through a flap valve, and passes to the surface through a large diameter pipe, called a rising main, which is fixed in the shaft near the pump rods.

The typical Cornish engine (dating from the early 19th century) had its huge beam mounted on the strengthened end wall of the engine house so that the mechanism was indoors and the end of the beam, with pump rods extending down the mine-shaft was in the open air.

What the engine did was to raise the pump rods and, with them, the plungers in the pumps, thus filling them with water. When the steam valve shut, the rods descended again under their own great weight, with an ‘equilibrium valve’ opening at the right moment to allow the expanded steam to fill the space below the piston as it rose. Closure of this valve as the piston approached the top of its stroke cushioned the descent of the rods, bringing them gently to rest so that the pumps could take the water at their own natural speed. The engine then paused at the top of its stroke until the cataract allowed the steam valve to open and repeat the cycle. The valves were adjustable to cope with whatever quantity of water needed pumping out, and it used to be said by engineers that a good engine could work at ten strokes per minute. To the miners in the gloomy, candlelit galleries far below ground, the sound of the pump echoed for miles, sounding like a giant snore and giving them constant assurance that all was well.

External links

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--Jcroggon 15:05, 30 May 2012 (EST)