The invention relates to a device for automatic adding of a coagulant for treatment of roof high
pollution runoff in a building downpipe. The device comprises a downpipe, an upper standpipe and a lower standpipe that are connected to the downpipe, a chemical dosing cylinder inclinedly communicated with the upper standpipe and the lower standpipe, and an
evaporation tank that is disposed above the chemical dosing cylinder and is communicated with the upper standpipe and the chemical dosing cylinder respectively, and a
brake lock valve body communicated with the chemical dosing cylinder is arranged below the
evaporation tank. According to the invention, a rainwater collection
pipe of an
evaporation tank chamber and a chemical dosing cylinder water collecting chamber inclined plate are disposed in the standpipes, the evaporation tank is internally equipped with a
piston, a connecting rod and a one-way
braking system, wherein the one-way
braking system depends on the cooperation of a spring leaf, a
brake pin and a connecting hinge to complete chemical dosing control. The device provided by the invention can effectively treat overflow rainwater falling into the downpipe, and can completely rely on the falling water
gravitational potential energy to complete initial rainwater water recognition and coagulant adding. The device has the characteristics of simple structure, convenient
processing and manufacture, complete autonomic regulation, convenient replacement of coagulant and good
treatment effect.