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. Subsequently other variants of sun valve were developed for various different uses.
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 expands the dark rod, switching a valve to cut the gas supply. After sunset, the central rod cools down, contracting to become 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. 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.
In 1921 Francis Everard Lamplough (an engineer with AGA's rival firm in lighthouse provision: Chance Brothers) patented an alternative 'light valve' in the hope of breaking Dalén's effective monopoly. In subsequent years it was installed on several lighthouses and beacons, but because of its dependence on liquid it could only be used in static locations (unlike Dalén's valves, very many of which were installed on floating buoys). Lamplough's 'valve' was a form of rocker switch, on which were mounted two glass bulbs, one black, the other clear, part-filled with liquid ether and linked by a tube. During the day, heat from the sunlight would cause the air in the black bulb to expand, forcing the liquid into the clear bulb, the additional weight tipping the switch and cutting off the current to the lamp; at night, or at other times of insufficient daylight, the process was reversed, reconnecting the current.
- The Sun Valve, History from the AGA website (archived link).
- 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.
- "Historical Monuments". Chumbe Island Coral Park. Archived from the original on 2017-07-26.
- Patent listing
- Chance, Toby; Williams, Peter (2008). Lighthouses: the Race to Illuminate the World. London: New Holland Publishers (UK) Ltd. p. 243.
- "Photo". Shipping Wonders of the World (3). 27 February 1936. Retrieved 21 March 2019.
- Patent No. US1997598