A sun valve
, "solar valve") is a form of flow control valve
, notable because it earned its inventor Gustaf Dalén
the Nobel prize in physics
The valve formed part of the Dalén light which was used in lighthouses from the 1900s through to the 1960s by which time electric lighting came to dominate.
The valve is controlled by four metal rods enclosed in a glass tube. One rod is blackened, while the others are highly polished. As daylight made the rocks visible, the heat of the sun allowed the expanding dark rod to cut the gas supply.
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