Backflow is a plumbing term for an unwanted flow of water in the reverse direction.[1]​ An example of this would be the case of the toilet cistern and its water supply, which must be isolated from the toilet bowl.

Backflow can present a serious health risk due to contamination of drinking water supplies with wastewater. Cross connections are links through which contamination is likely to enter a potable water supply when the pressure of the contaminated source exceeds the pressure of the potable source. The action may be referred to as “backsiphoning” or “back pressure.”[2] For this reason, building codes require a number of measures and devices in order to prevent backflow, either by eliminating cross connections or by preventing backflow where cross connections cannot be eliminated.

Contenido

La prevención de reflujo debe ser automática. Válvulas operadas manualmente no suelen ser aceptables.

Non-return valves

Non-return valves close the passage of a circulating fluid (gaseous or liquid) in one direction and leave free passage in the opposite direction. Its process is linked to the changes of fluids to open and close, that is, its operation is automatically mechanical.

This type of valve detects the flow of a process by opening at a certain pressure in the same direction and closing in the opposite direction when the flow decreases or loses pressure.

air spaces

Reverse siphoning can be avoided by using a vertical air gap. The size of the acceptable gap depends on the capacity of the incoming supply, so that a clogged flow cannot overfill the cistern and close the gap.

Air gaps can also protect against back pressure and are generally preferred for this.[3] However, most air gaps also limit the system pressure that can be transmitted through them.

Sanitary backflow valves are intended to prevent the backflow of wastewater into the sanitary sewer line during a sewer flood or blockage, and have no connection to potable water.