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Beam Engine

Today's Mural by Jim Corsiter
Beam Engine Mural

The Engine

The engine was manufactured by Messrs. Harvey & Co., of Hayle, Cornwall, in 1874. The parts were shipped from Corn- wall to Morison's Haven harbour, adjacent to the colliery, and It is assumed that the engine beam, weighing approximately 30 tons, was raised into position in stages by means of jacks, as the building of the engine house progressed. The Beam is 33 ft. long and 6 ft. 4 ins. deep at the centre. The fulcrum is 18 ft. from the steam end. The cylinder is 70" diameter x 12'0" stroke. The trunnion is located off centre, giving the pump rams a stroke of 10'0". The normal speed of the engine is 3Vs strokes per minute and the pumping capacity was 650 gallons of water per minute allowing an efficiency of 70%.

The Engine still stands for the 21st Century
The Engine still stands for the 21st Century

Valve Mechanism
The engine is fitted with three operating valves of the double beat balanced type (Cornish Valves) opened by means of dead weights, levers and trip rods actuated by the release of detents and controlled by cataracts situated below floor level. The cataracts are simply water tanks containing floats attached to the detent trip rods and the operation of the valves is controll- ed and timed by regulating the size of opening through which the water from the tank is released. The valves are closed by means of adjustable tappets attached to the plug rod suspend- ed from the engine beam. The three main valves for controll- ing the engine are the steam valve for admitting steam to the top of the piston, the exhaust valve for releasing the steam on the bottom side of the piston to the condenser during the downstroke and the equilibrium valve which is opened at the end of the downstroke, allowing steam to flow from the top to the bottom of the piston during the upstroke. A water in- jection valve is also fitted to admit water to the condenser at the end of the upstroke when the exhaust valve opens.

The Working Cycle
The working cycle of the engine for a complete stroke is as follows:- Steam at boiler pressure is admitted to the top of the cylinder viathe Steam valve, forcing the piston downwards and thus raising the pumprods and rams. At the start of the downstroke, therefore, the steam valve is open.the exhaust valve from the bottom of the cylinder to the condenser is open and the equilibrium valve is closed. At a predetermined point near the bottom of the stroke, the steam valve closes and the downward stroke is completed by the expansion of the steam in the cylinder. When the piston has reached the bottom of the stroke, the equilibrium valve opens and the ex- haust valve closes, allowing the steam to flow from the top side of the piston to the bottom side. Both sides of the piston are now in a state of equilibrium and the dead weight of the pumprods and rams starts the pumping stroke, causing the piston to travel upwards. Shortly before the piston reaches the top of the stroke, the equilibrium valve closes and the piston is brought gently to rest due to compression of the steam re- maining in the top part of the cylinder. The exhaust valve now opens, also the injection valve to the condenser, thus creating a vacuum in the cylinder below the piston. The steam valve then opens and the cycle is repeated.

Some years after Prestongrange Colliery was taken over by the Summerlee Iron Company in 1895, it became necessary to in- crease the capacity of the shaft pumps and It was decided to install 28" diameter rams. The main pumps consist of two 28" force pumps, one at the Great Seam level, and one about midway between thatand the surface, raising the water in two stages. At the Beggar Level, below the Great Seam, is another pump 17" diameter, which pumps to the Great Seam lodge- ment. The pump rods, of Oregon pine, are 23" square from the surface to the top lift pump and the total weight of the pump rods, rams, crossheads and side rods is about 105 tons. Calculations of the engine beam strength showed that the beam as it stood was not capable of bearing the extra load im- posed by the installation of the larger pumps, consequently a strengthening truss was designed. Fitting of this truss was no mean feat, bearing in mind that, at that time, no electrical power was available for drilling machines.etc. A specially con- structed boring bar, driven by a small steam engine was used for drilling the large holes in the sides of the beam to receive the pins in the eyes of the tiebars. When the truss had been erected, a system of levers was fitted to the beam for the pur- pose of measuring the deflection to ensure that the beam was not unduly stressed when tightening the tie bars.

Mishaps To Cylinder
About 1916, a serious mishap occurred due to the fracture of the piston rod when the piston was at the top of the stroke. The impact caused by the falling piston broke the cylinder bottom and cracked the cylinder wall. A new cylinder bottom was cast and it was decided to attempt to repair the cylinder by clamping. Heavy cast iron rings were made in halves and these were bolted together round the cylinder. The cracks were caulked with a mixture of red lead and boiled linseed oil, after which the set-screws round the rings were tightened to close the cracks. No further trouble was experienced until 1938 when the piston rod again broke under the same condi- tions. Another cylinder bottom was fitted and the repair of the walls was achieved by removing the clamping rings and cutting dovetailed grooves inserting and clamping up strips of soft copper. The engine continued working until pumping by means of the Cornish Pump finally ceased in 1954.

Beam Engine Mural

The Historical Site
The Beam Engine, now an Industrial Monument, is the centre-piece of a Historical Site for the Mining Industry. The first written record of coal mining in Britain Is the Charter given to the monks of Newbattle in 1210 to work the coal in the Grange of Preston. The first coal 'harbour, Acheson's Haven, lay across the road and the first railway in Scotland was laid on wooden rails from Tranent to Cockenzie, some three miles down the coast.

These and other noticeable landmarks are accessible today via The Coal Trail.

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