The applications listed here emphasize foam as a delivery system for herbicides designed to kill roots in sewer systems.  Although the technology seems fairly simple, there are many unseen complications - most notably, and not obvious at first glance, is the pressure required for pushing the foam through long lengths of sewer pipe compared to the pressure drop connecting the laterals feeding the main sewer line - one does not want the sewer foam venting through your kitchen sink!!

Horne, F.F., U.S. Patent 3,874,926, April 1, 1975
Method and Apparatus for Injecting Foam into a Pipe

Horne, F.F., U.S. Patent 3,880,176, April 29, 1975
Apparatus for Sewer Treatment to Kill Tree Roots and Other Organic Growth Therewithin

Horne, F.F., U.S. Patent 3,892,588, July 1, 1975
Method of Killing Roots and organic Growths in Sewer Pipes

Horne, F.F., U.S. Patent 4,025,360, May 24, 1977
Method and Apparatus for Injecting Foam into a Pipeline, Including an Inflatable Plug

Horne, F.F., U.S. Patent 4,083,384, April 11, 1978
Method and Apparatus for Injecting Foam into a Pipeline, Including an Inflatable Plug

Monaghan, J.D., U.S. Patent 5,735,955, April 7, 1998
Apparatus for Generating and Dispersing Foam Herbicide Within a Sewer

Malavenda, A., U.S. Patent 5,919,731, July 6, 1999
Method for Controlling Root Growth Using Diquat Bromide

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