Hydraulic ram

A hydraulic ram, also known as a hydram, is a cyclic water pump powered by hydropower. It is a clever machine that uses the energy of flowing water to move water to a higher location. The pump takes in water at a specific hydraulic head, which is the pressure of the water, and a certain flow rate. It then outputs water at a much higher hydraulic head, but at a lower flow rate.

This device is especially useful in remote areas. These locations might have a source of low-head hydropower but need water delivered to a higher elevation. Because the ram relies on the kinetic energy of flowing water, it requires no outside power source like electricity.

The mechanism of the pump relies on a phenomenon called the water hammer effect. To understand how it works, we must look at the sequence of its operation. Initially, the waste valve, sometimes called a clack valve, is open due to its own weight. The delivery valve remains closed because of the static pressure in the outlet. Water begins to flow through the inlet pipe, picking up speed and kinetic energy from gravity. As the water moves, the drag force eventually lifts the weight of the waste valve, causing it to close abruptly.

When the waste valve shuts, the momentum of the flowing water creates a water hammer. This is a sudden increase in pressure that rises above the static pressure of the outlet water column. This pressure differential forces the delivery valve open, allowing a portion of the water to flow into the delivery pipe. This water is pushed uphill to a higher destination. As the water flow slows or reverses, the delivery check valve closes to prevent backflow. Meanwhile, the pressure pulse travels back up the inlet pipe as a suction pulse. This pulse pulls the waste valve back into its open position, allowing the cycle to repeat.

Traditional hydraulic rams are known for being extremely reliable and easy to maintain. This is because they typically contain only two moving parts: the waste valve and the delivery valve. To improve performance, many systems include a pressure vessel containing an air cushion. This air cushion softens the hydraulic pressure shock when the waste valve closes. Without this vessel, the pump's efficiency would drop drastically, and the machine would face extraordinary stresses. To keep the air in the vessel, engineers sometimes use a snifting valve to inhale small amounts of air. Another practical solution is inserting a bicycle or car tire tube into the vessel to act as a diaphragm.

The history of the hydraulic ram involves several important inventors and engineers. In 1772, John Whitehurst of England invented a manual precursor called the pulsation engine. He installed his first device at Oulton, Cheshire, to raise water to a specific height. In 1796, the Frenchman Joseph Montgolfier invented the first self-acting ram pump for his paper mill. His friend, Matthew Boulton, obtained a British patent for this design in 1797. Later, the engineer Josiah Easton acquired these designs and built a major firm. His company supplied rams to large country houses, farms, and entire village communities throughout the nineteenth century.

Efficiency is a key factor in how these pumps perform in real-world settings. A typical hydraulic ram has an energy efficiency of about 60%, though some can reach up to 80%. It is important to distinguish this from volumetric efficiency, which is the ratio of water delivered to the total water taken from the source. For example, if a pump has a 2-to-1 supply-head-to-delivery-head ratio and 70% efficiency, the delivered water would be 35% of the supply.

The design of the drive pipe is also critical for success. The drive pipe should ideally be between 3 and 7 times longer than the vertical distance between the source and the ram to ensure reliable cycling.

Interest in the hydraulic ram has changed over the decades. In the United States, Joseph Cerneau and Stephen S. Hallet received the first patent in 1809. Interest in the U.S. grew around 1840, but waned toward the end of the 19th century as electricity became common. One notable example is Priestly's Hydraulic Ram, built in Idaho in 1890, which is now on the National Register of Historic Places. Today, interest in the technology has revived. It is being used for sustainable technology in developing countries and for energy conservation in developed nations. Engineers like Frederick Philip Selwyn have even developed more compact versions, such as the "Papa Pump," which uses the venturi effect to improve design.