Editing Water wheel (section)

=== Stream ===
[[File:Stream waterwheel simple.svg|thumb|150px|Stream shot waterwheel]]

A stream wheel<ref name="Stream wheel term and specifics"/><ref name="PITLtypes"/> is a vertically mounted water wheel that is rotated by the water in a water course striking paddles or blades at the bottom of the wheel. This type of water wheel is the oldest type of horizontal axis wheel.{{citation needed|date=April 2017}} They are also known as [[free surface]] wheels because the water is not constrained by millraces or wheel pits. {{citation needed|date=April 2017}}

Stream wheels are cheaper and simpler to build and have less of an environmental impact than other types of wheels. They do not constitute a major change of the river. Their disadvantages are their low efficiency, which means that they generate less power and can only be used where the flow rate is sufficient. A typical flat board undershot wheel uses about 20 percent of the energy in the flow of water striking the wheel as measured by English civil engineer [[John Smeaton]] in the 18th century.<ref>The History of Science and Technology by Bryan Bunch with Alexander Hellmans p.&nbsp;114</ref> More modern wheels have higher efficiencies.

Stream wheels gain little or no advantage from the head, a difference in water level.

Stream wheels mounted on floating platforms are often referred to as hip wheels and the mill as a [[ship mill]]. They were sometimes mounted immediately downstream from [[bridges]] where the flow restriction of the bridge piers increased the speed of the current.{{citation needed|date=April 2017}}

Historically they were very inefficient but major advances were made in the eighteenth century.<ref name="ASMEnoria">{{cite web
|url=https://www.asme.org/wwwasmeorg/media/resourcefiles/aboutasme/who%20we%20are/engineering%20history/landmarks/241-noria-al-muhammadiyya.pdf
|title=Noria al-Muhammadiyya
|publisher=The American Society of Mechanical Engineers
|author=The American Society of Mechanical Engineers
|access-date=12 Feb 2017
|date=December 2006
}}</ref>