Cash Acme 3/4 inch Dual Check Backflow Preventer Valve. Cash Acme feet s BF-1 Series Dual Check Backflow Preventers are designed to prevent polluted water from entering the potable water supply system by stopping the reverse flow of water into supply lines. The BF Series is designed to protect the primary water system (such as city water supply) by providing containment at the point of distribution. These valves function in either the horizontal or vertical position under continuous or intermittent pressure conditions.