Gun barrel settling tank

Wash tank or, as it is more commonly called, a gun barrel–is a settling tank fitted with an internal or external boot, or flume. Although gun barrels are not employed to the extent now that they once were, many are still used to break emulsions.

In a gun barrel, oil and water are separated in a two-part action: (1) washing, and (2) settling. The washing is done in the free-water layer, and the settling occurs in the emulsion layer. Because all emulsions are not alike, the amount of free water that should be held in a gun barrel must be established for each lease. For instance, if washing has little or no effect on a certain emulsion, then only a small amount of free water is maintained in the gun barrel’s tank. Conversely, if an emulsion completely breaks down by washing, then a large amount of free water is kept in the tank.