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This is the only surviving example of a complete Newcomen engine on its original site.
Built in 1794-95, it was used to pump water from the mines owned by Lord Fitzwilliam. The original 42" diameter cylinder was replaced as early as 1801 by one of 48" diameter, and the wooden beam was replaced by the existing cast iron beam in 1836. The engine ran until 1923 when electric pumps were installed, and was retained as standby until 1930. It was then retained in working order with occasional demonstration steamings until 1953 when one such demonstration is believed to have resulted in some damage. It came into the possession of Barnsley Metropolitan Council in 1988, having accorded Scheduled Monument status in 1972. In early 2012 the Heritage Lottery Fund made a grant of £425,000 to restore the engine to full working order. Whether this will include the provision of a steam supply is not stated.
The Newcomen engine works on what is known as the atmospheric principle. That is to say that it is not steam pressure which operates it, but the force of atmospheric pressure working against a vacuum. The vacuum is created by admitting steam to the cylinder when the piston is at the top of its stroke. A jet of cold water is then injected into the cylinder. This condenses the steam into water, creating a vacuum in the cylinder. The atmospheric pressure acting on the top of the piston pulls it down, together with the end of the beam to which it is attached. The other end of the beam pulls up a pump rod which works a simple pump at the bottom of the mine. Steam is now admitted to the cylinder again, and the weight of the pump rods raises the piston to allow the cycle to start all over again.
The Elsecar engine ran at about 6-8 strokes a minute, raising about 50 gallons of water per stroke.