Screens and flap gates have historically been installed on overflow pipes, but those have become inferior technology for protecting tanks from birds, animals, airborne pathogens, and most recently risk of terrorist attack.
Screens can rust, become dislodged, collect materials like leaves in the overflow pipe, encourage icing on the screen when the surfaces are wet (screen gets blown out on next overflow), do not prevent insects from entering the tank, and do not prevent cold drafts from entering the tank thru the overflow pipe which can promote icing.
Flap gates can hang open and can corrode or rust in the open or closed position. Consider, the Tideflex Valve was invented based on a USEPA grant whose purpose was to overcome operational and maintenance problems associated with flap gates.
Tideflex Valves are extensively used for overflow pipe protection because they are all rubber so they cannot rust or corrode, are non-mechanical so they don’t require maintenance and completely drain after an overflow event. Tideflex Valves also prevent cold drafts from entering the tank which can promote icing in cold climates. For end-of-pipe applications, Tideflex are available in slip-on (Series TF-1 or TF-2) or flanged connections (Series 35-1 or 35) and are supplied with stainless steel clamps or retaining rings (Figures 1 & 2).