|pipeline = surge_tank|
|A tank designed to absorb excessive water power in a pipeline on valve closing or emergency stops|
|Used on these elements|
|Tools for this tag|
Surge tanks are useful to dissipate the power water is applying to pipes and tunnels when a valve is closed (sometimes brutally).
Depending of upstream (only, not downstream penstocks) tunnels length and diameter, they can be pretty huge shafts like 200m of depth and 20m of diameter - often found in the middle of nowhere.
Overground building can exist sometimes and it may be useful to add name=Valve chamber on it.
Surge tanks is a concept related to fluid flows, not specific to penstocks.
As strategic function of a pipeline system, often at the start point of penstocks, we can map them in OSM with pipeline=surge_tank on a node only, like valves.
Even if such tanks can be huge shafts or chimneys, pipeline=surge_tank should be used on a pipeline node placed at the position of the tank. Visible infrastructure can be tagged with man_made=shaft or man_made=chimney since it can be complex buildings or construction which don't need to be linked to pipeline directly.
How to map
|pipeline||surge_tank||It's a pipeline surge tank||mandatory|
|location||<tank location>||Location of the surge tank. Can be outdoor, underground||recommanded|
|diameter||<tank diameter>||The internal diameter of the tank||optional|
|operator||<surge tank operator>||Name of the company operating the surge tank||optional|
|--||A chimney is installed above the pipeline it is supposed to protect|
|--||Here is an underground shaft acting as a surge tank for a penstock located 170 metres below. The shaft outlet is about 18 metres wide|