divided by the initial jet power, is the turbine efficiency, η = 4u(Vi − u)/Vi2. It is zero for u = 0 and for u = Vi. As the equations indicate, when a real Pelton wheel is working close to maximum efficiency, the fluid flows off the wheel with very little residual velocity. In theory, the energy efficiency varies only with the efficiency of the nozzle and wheel, and does not vary with hydraulic head. The term "efficiency" can refer to: Hydraulic, Mechanical, Volumetric, Wheel, or overall efficiency. System components The conduit bringing high-pressure water to the impulse wheel is called the penstock. Originally the penstock was the name of the valve, but the term has been extended to include all of the fluid supply hydraulics. Penstock is now used as a general term for a water passage and control that is under pressure, whether it supplies an impulse turbine or not. See also Peltric set Centrifugal pump References External links Example Hydro at Dorado Vista ranch American inventions Water turbines 19th-century inventions