3/4" 34-460XL Zorn Wilkins, Lead-Free Spill Resistant Pressure Vacuum Breakers are for use on potable water lines where a health hazard could exist if a backs phone situation were to occur. They must not be installed where backpressure may occur. Proper performance depends upon following these installation instructions and prevailing governmental and industry standards and codes. Failure to do so releases ZURN WILKINS of any liability that it might otherwise have with respect to that device. Such failure could also result in an improperly functioning device. Spill Resistant Pressure Vacuum Breaker Assy.