Per Febco 905-051 765 Kit Riparazione Gruppo Valvola di Ritegno, 1/2"/3/4", 905051, 765CBV
(3) First replace the parts. you need to first close the outlet valve, then quickly turn on the inlet valve. Then you can turn on the outlet valve, completing the repair. It is for use to repair check valve on 1/2" & 3/4" model 765.