A hyraulic ram 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.