hydraulic ram

A hydraulic ram that drives a fountain at the Centre for Alternative Technology

A hydraulic ram is a water-powered cyclic pump. It harnesses the forces of water hammer to pump a portion of the water being used to power the pump to a point higher 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 kinetic energy of falling 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 1775 at Oulton, Cheshire, raised water to a height of 16 ft (4.9m). 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. 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 spring or weight loaded "waste" valve sometimes known as the "clack" valve and a "delivery" 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.

Sequence of operation

Hydraulic ram:
1. Inlet - drive pipe;
2. Free flow at waste valve;
3. Outlet - delivery pipe;
4. Waste valve;
5. Delivery check valve;
6. Pressure vessel

Initially, the [4] waste valve is open, the [5] delivery valve is closed. The water in the [1] drive pipe starts to flow under the force of gravity and picks up speed and kinetic energy until it forces the waste valve closed. The momentum of the water flow in the supply pipe against the now closed waste valve causes a water hammer, raises the pressure in the pump and opens the delivery valve [5], so some water flows into the delivery pipe [3]. Since this water is being forced uphill through the delivery pipe farther than it is falling downhill from the source, the flow slows down and when it reverses the delivery check valve closes. If all water flow has stopped, the loaded waste valve reopens against the now static head, allowing the process to begin again.

A pressure vessel [6] containing air, cushions the hydraulic pressure shock when the waste valve closes, and it also improves the pumping efficiency by allowing a more constant flow through the delivery pipe. Although, in theory, the pump could work without it, the efficiency would drop drastically and the pump would be subject to extraordinary stresses which would shorten its life considerably. This air is under pressure and is gradually dissolved in the water until none remains. One solution to this problem is to have the air separated from the water by an elastic diaphragm, (similar to an "expansion tank"), however this solution can be problematic in third world countries where replacements are difficult to procure. Another solution is to have a mechanism such as a "snifting valve" which automatically inserts a small bubble of air with each pump cycle. [1]

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 delivery 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. The drive pipe is ordinarily straight but can be curved or even wound in a spiral. The main requirement is that it be inelastic, strong and rigid as otherwise it would greatly diminish the efficiency.

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.

External links

• Details of how to make a homemade hydraulic ram
• Green and Carter
• HowStuffWorks-How does a hydraulic ram pump work?
• Information on hydraulic ram pumps
• A video of a hydraulic ram at work
• A video explaining the working of the hydraulic ram pump
• Picture of a hydraulic ram

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