Formsprag Model HSB pump backstopping clutches are used on a variety of wastewater applications including, clarifier tank sludge removal pumps, sludge and microorganism pumps, screw conveyors, and transfer pumps. FRB Series backstopping clutches and SB pump backstops can be used on some of the same applications. The clutches are used to prevent pump impellers from rotating backwards (backflow) when the pump motor is off and back pressure is present.