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Definition: The backflow preventer is a type of hydraulic control device which can strictly control the water inside pipeline to flow in one direction, and consisted of two separately functional check valves and a drain valve.

 Application:  The backflow preventer is applied to high, general, and low risk of contaminated area.

Design principles

Backflow preventer is consisted of three parts including inlet check valve, outlet check valve, and a drain valve located between the two check valves.

When the fluid flow normal in the pipe, the inlet pressure is always higher than the outlet pressure, and water goes through the assembly smoothly in normal direction. For the moment, the inlet pressure is greater than that in the valve chamber, and constitutes a positive pressure differential △P，which drives the drain valve in a closed position, and therefore there is no leakage from the drain valve. When the water flow gets to zero state, there is no water coming out from the outlet, and both the two check valves are in closed position. The pressure at the inlet, middle chamber, and outlet is in different pressure, but the inlet pressure is still greater than the pressure in the valve chamber to keep the drain valve in the closed position. If the inlet pressure goes down to produce backsiphonage tendency or the outlet pressure goes up to produce backpressure tendency, the positive pressure differential △P drops to a specified point; the drain valve opens to drain out water in the middle chamber, and air goes into the valve chamber to form air gap, thereby preventing the reverse flow from being pumped or siphoned to the portable water pipeline.

A.  Adopting two separate check valves structure, the two end springs of both check valves having relatively strong preload force ensure a quick action. Prior to occurring backpressure or backsiphonage reverse, check valves could complete actively, beforehand, and timely closed action.

B. The two separate spring assisting closed action of check valves system and the pressure differential drain valve system in middle chamber have no mechanically connection beside they are operated in one valve body. Such designing structure means these parts are operated independently, and therefore they will not turn up coexisted mechanical glitches and ensure a highest safe handling. .

C. Reduced-pressure type backflow preventer has been publicly regarded as backflow preventer control device with the highest safe protection class. It has gradually applied widely in domestic water supply engineering projects.