The article provides an example of calculating the elements of the sprinkler at automatic foam fire-extinguishing systems. There is Venturi tube at the core of the sprinkler. There are holes in the narrowest section for gas saturation of the extinguishing agent in data Venturi tube. This design allows the sprinkler to increase the effectiveness of fire-extinguishing foam due to its gas saturation, for example, the calculation of the hydrodynamic characteristics of the sprinkler taken universal foam. Data foam is approved for use in the Republic of Belarus. Injector elements are confuser, narrow (constriction) section and diffuser. To reduce losses, an injector inlet diameter is assumed to be the diameter of the output distribution pipe. This technique can be applied to the hydraulic design of automatic foam fireextinguishing systems.