Do flapper & ball type BWV’s provide a 100% positive seal?
No. The ANSI/ASME national standard allows for a minimal amount of seepage around the flapper or ball. The purpose of a flapper or ball is to suppress the back flow. Therefore, if the back flow condition exists over a lengthy period, there will be water seeping into the building at the lowest fixture or floor drain. For a 100% positive seal, you need to specify a figure number 7140 FloodGate BWV.
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