DF41 backflow Preventer/HS41 anti-fouling block valve consists of two separate check valves and a hydraulic drive-to-drain Valve. The first check valve body is fitted with a strainer. Due to the local head loss of the check valve, the pressure in the center chamber is always lower than the inlet pressure. This pressure difference drives the drain valve to be in the closed state and the water supply in the pipeline is normal.
When the pressure is abnormal （I.E. The outlet pressure is higher than the Middle Cavity） . even if both check valves can not be sealed in reverse, the safety drain valve can automatically open to drain the backflow and form air partition to ensure the sanitation and safety of the upstream water supply.
