Hydraulic ram

The use of the term hydraulic ram below describes a type of water pump. For the use of the term in vehicle extrication, see Jaws of Life.

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A hydraulic ram is a water-powered cyclic pump. It harnesses the "water hammer" effect to pump a portion of the water being used to power the pump to a higher point than where the water originally started. It is sometimes used in remote areas where the right conditions exist, since it requires no outside source of power other than the energy of falling water.

History

James Whitehurst, FRS (1713-1788) installed a water raising machine in 1775 at Oulton, Cheshire. It raised water to a height of 16ft. He installed another in an Irish property in 1783. He did not patent it, and details are obscure, but it is known it had an air vessel.

The first self-acting ram pump was invented by the Frenchman Joseph Michael Montgolfier in 1796 for raising water in his paper mill at Voiron. His friend Matthew Boulton took out an English patent on his behalf in 1797. The sons of Montgolfier obtained an English patent for an improved version in 1816, and this was acquired in 1820 by James Easton, a young Somerset engineer, who had just moved to London. Easton's firm grew during the nineteenth century to become one of the more important engineering manufacturers in Britain, 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 survive [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. Green & Carter now function from Ashbrittle, nr Wellington, Somerset.

The first American patent was issued to J. Cerneau and S.S. Hallet in 1809. American 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.

Construction and Principle of Operation

A hydraulic ram has only two moving parts, a ?waste? valve (sometimes known as the ?clack? valve) and a ?delivery? valve (or ?check? valve), making it cheap to build, easy to maintain, and very reliable. In addition, there is a drive pipe supplying water from an elevated source, and a delivery pipe, taking a portion of the water that comes through the drive pipe to an elevation higher than the source. The waste valve is held open by a spring or gravity, allowing water from the drive pipe to drain into the open. When the flow of water is fast enough, it forces the waste valve closed, and it remains closed until the pressure is relieved. The delivery valve is held closed by a spring or by the pressure of the water in the delivery pipe unless the pressure at the end of the drive pipe is greater than that in the delivery pipe, in which case it opens and allows water to flow from the drive pipe into the delivery pipe.

The sequence of operation is as follows. Initially, the waste valve is open, the delivery valve is closed, and the water is at rest. The water in the drive pipe starts to flow under the force of gravity and picks up speed until it forces the waste valve closed. The inertia of the moving water raises the pressure and opens the delivery valve, so that water starts flowing into the delivery pipe. Since the water is being forced uphill through the delivery pipe farther than it is falling downhill from the source, the flow slows down and the pressure drops. At some point the delivery valve closes and the waste valve reopens, allowing the process to begin again.

A common refinement is to add a pressure vessel containing some air between the pump and the delivery pipe. This cushions the shock when the waste valve closes and improves the efficiency by allowing a more constant flow through the delivery pipe. In a similar way a supply pipe and a barrel (or a stand pipe) may be added above the drive pipe so that the drive pipe does not have to be made too long. The optimum length of the drive pipe is 5 to 12 times the vertical distance between the source and the pump, or 500 to 1000 times the diameter of the drive pipe, whichever is less. This length of drive pipe typically results in a period between pulses of 1 to 2 seconds. A typical efficiency is 60%, but up to 80% is possible.

Common Operational Problems

Some common operational problems are intrusion of air into the drive pipe, blockage of the intake or valves with debris, knocking due to too little air in the pressure vessel, and freezing in winter.

Links

For Green & Carter see

For PDF paper on hydraulic ram pumps by the hydraulics, Jaws of Life