Sun valve

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Sun valve designed by Gustaf Dalen, 1912, TM34299 - Tekniska museum - Stockholm

A sun valve (Swedish: solventil, "solar valve") is a flow control valve that automatically shuts off gas flow during daylight. It earned its inventor Gustaf Dalén the 1912 Nobel Prize in Physics.

The valve was the key component of the Dalén light used in lighthouses from the 1900s through the 1960s, by which time electric lighting was dominant.

Prominent engineers, such as Thomas Edison, doubted that the device could work. The German patent office required a demonstration before approving the patent application.[1]


The valve is controlled by four metal rods enclosed in a glass tube. The central rod that is blackened is surrounded by the three polished rods. As sunlight falls onto all of the rods, the absorbed heat of the sun allows the unequally expanding dark rod to cut the gas supply. After sunset, the central rod cools down, becoming the same length as the polished rods and opening the gas supply. The gas is lit by the small, always-burning pilot light.


Dalen's system of acetylene lighting for marine navigation proved very reliable, as exemplified by the lighthouse at Chumbe Island off Zanzibar. This lighthouse was constructed in 1904 and converted to un-manned automatic acetylene gas operation in 1926.[2] The acetylene lighting installation, controlled by a sun valve, remained in use until the lighthouse was converted to a solar-powered (photovoltaic) system in 2013.[3]


  1. ^ The Sun Valve, History from the AGA website (archived link).
  2. ^ Jeremy D'Entremont (August–September 2004). "Zanzibar's Chumbe Lighthouse Celebrates a Century of Service". Lighthouse Digest. Archived from the original on 2017-07-26.
  3. ^ "Historical Monuments". Chumbe Island Coral Park. Archived from the original on 2017-07-26.