Board Thread:Questions and Answers/@comment-13037480-20130806032024/@comment-13413401-20130806222132

Did you say that the sewage collectors have the silver upgrades? You have to be careful when placing upgrades in the sewage collectors. If the ranges of 2 or more sewage collectors overlap, they will both stop working...

So if the sewage collectors are right next to each other, then the ranges will overlap because each silver upgrade improves the range by 6 blocks.