A hydraulic ram, or hydram, is a cyclic water pump powered by hydropower. It functions as a hydraulic transformer that takes in water at one hydraulic head and flow-rate, and outputs water at a different hydraulic-head and flow-rate. The device utilizes a phenomenon called stagnation pressure, also known as water hammer, that is based on Bernoulli's principle. In operation, a portion of the input water that powers the pump is lifted to a point higher than where the water originally started. The hydraulic ram is sometimes used in remote areas, where there is both a source of low-head hydropower, and a need for pumping water to a destination higher in elevation than the source. In this situation, the ram is often useful, since it requires no outside source of power other than the kinetic energy of water.
History
In 1772 John Whitehurst of Cheshire in the United Kingdom invented a manually controlled precursor of the hydraulic ram called the "pulsation engine". The first one he installed, in 1772 at Oulton, Cheshire, raised water to a height of 16 ft (4.9 m). He installed another in an Irish property in 1783. He did not patent it, and details are obscure, but it is known to have had an air vessel.
The first self-acting ram pump was invented by the Frenchman Joseph Michel Montgolfier in 1796 for raising water in his paper mill at Voiron. His friend Matthew Boulton took out a British patent on his behalf in 1797. The sons of Montgolfier obtained an English patent for an improved version in 1816, and this was acquired, together with Whitehurst's design, in 1820 by Josiah Easton, a Somerset-born engineer who had just moved to London.
Easton's firm, inherited by his son James (1796–1871), grew during the nineteenth century to become one of the more important engineering manufacturers in the United Kingdom, with a large works at Erith, Kent. They specialised in water supply and sewerage systems world-wide, as well as land drainage projects. Eastons had a good business supplying rams for water supply purposes to large country houses, and also to farms and village communities, and a number of their installations still survived as of 2004.
The firm was eventually closed in 1909, but the ram business was continued by James R Easton. In 1929 it was acquired by Green & Carter, of Winchester, Hampshire, who were engaged in the manufacturing and installation of the well-known Vulcan and Vacher Rams.
The first US patent was issued to J. Cerneau and S.S. Hallet in 1809. US interest in hydraulic rams picked up around 1840, as further patents were issued and domestic companies started offering rams for sale. Toward the end of the 19th Century, interest waned as electricity and electric pumps became widely available.
By the end of the twentieth century interest in hydraulic rams has revived, due to the needs of sustainable technology in developing countries, and energy conservation in developed ones. A good example is AID Foundation International in the Philippines, who won an Ashden Award for their work developing ram pumps that could be easily maintained for use in remote villages. The hydraulic ram principle has been used in some proposals for exploiting wave power, one of which was discussed as along ago as 1931 by Hanns Günther in his book In hundert Jahren.
