Editing Water turbine (section)

=== New concept ===
{{Main|Pelton wheel}}
[[File:Pelton wheel (patent).png|thumb|right|Figure from  [[Lester Allan Pelton|Pelton's]] original patent (October 1880)]]

All common water machines until the late 19th century (including [[water wheel]]s) were basically reaction machines; water ''pressure'' head acted on the machine and produced work.  A reaction turbine needs to fully contain the water during energy transfer.

In 1866, California millwright Samuel Knight invented a machine that took the impulse system to a new level.<ref>W. A. Doble, "The Tangential Water Wheel", ''Transactions of the American Institute of Mining Engineers'', Vol. XXIX, 1899.</ref><ref>W. F. Durrand, ''The Pelton Water Wheel'', Stanford University, Mechanical Engineering, 1939.</ref> Inspired by the high pressure jet systems used in hydraulic mining in the gold fields, Knight developed a bucketed wheel which captured the energy of a free jet, which had converted a high head (hundreds of vertical feet in a pipe or [[penstock]]) of water to kinetic energy. This is called an impulse or tangential turbine. The water's velocity, roughly twice the velocity of the bucket periphery, does a U-turn in the bucket and drops out of the runner at low velocity.

In 1879, [[Lester Allan Pelton|Lester Pelton]], experimenting with a Knight Wheel, developed a [[Pelton wheel]] (double bucket design), which exhausted the water to the side, eliminating some energy loss of the Knight wheel which exhausted some water back against the center of the wheel. In about 1895, William Doble improved on Pelton's half-cylindrical bucket form with an elliptical bucket that included  a cut in it to allow the jet a cleaner bucket entry. This is the modern form of the Pelton turbine which today achieves up to 92% efficiency. Pelton had been quite an effective promoter of his design and although Doble took over the Pelton company he did not change the name to Doble because it had brand name recognition.

[[Turgo turbine|Turgo]] and [[cross-flow turbine]]s were later impulse designs.