RPZ - Backflow Preventer | Detailed explanations




Potable water from the mains supply may be subject to pollution caused mainly by the contaminated fluids flowing back from plumbing installations connected directly to the mains supply. Backflow can be attributed to a variation in the pressure difference that causes a consequent inversion of the normal direction of flow at certain point of the installation. This phenomenon, termed “backflow”, occurs when:


a) the pressure in the mains system is less than that in the plumbing circuit receiving the supply (back syphonage). This situation can occur, for example, due to a break in the pipework of the mains supply and the consequent maintenance work, or when significant quantities of water are drawn by other users connected upstream, such as fire-fighting systems

b) the pressure in the plumbing circuit receiving the supply rises (back pressure) due, for example, to water being pumped from a well.

Risk assessment

Given the potential danger of the phenomenon and the requirements of current regulations, the risk of pollution by backflow must be assessed on the basis of the type of system and the characteristic of the fluid that flows in it. An appropriate backflow prevention device must be selected on the basis of that assessment performed by the system designer and the mains supply Company. The device must be located along the supply line at those points at risk of backflow which would be hazardous to human health.


The protection can be provided by inserting a backflow preventer at critical points in the circuit at the inlet from the mains supply network or in the internal distribution system. This will prevent polluted water from flowing back in all systems for which direct connection to the mains supply network or an internal supply is considered hazardous.

Protection Unit - Product standards - Caleffi devices

Use of backflow preventers (BA type) according to European standards EN 1717 and EN 12729 

Proper use of the BA type backflow preventer is regulated by the European standards on the prevention of pollution by backflow. The relevant standard is EN 1717: 2000 “Protection against pollution of potable water in water installations and general requirements of devices to prevent pollution by backflow”. The types of water contained in water systems are classified in this standard according to the degree of risk to human

Category 1:
Water to be used for human consumption coming directly from a potable water distribution system.

Category 2:
Fluid presenting no human health hazard. Fluid recognized as being fit for human consumption, including water taken from a potable water distribution system, which can have undergone a change in taste, odour, color or temperature (heating or cooling).

Category 3:
Fluid representing some human health hazard due to the presence of one or more harmful substances.

Category 4:
Fluid representing human health hazard due to the presence of one or more toxic or very toxic substances or one or more radioactive, mutagenic or carcinogenic substances.

Category 5:
Fluid presenting a human health hazard due to the presence of microbiological or viral elements.

Appropriate backflow prevention devices must be fitted in water supply systems on the basis of this classification.

Backflow preventers (BA type) can be used to protect against the risk of pollution from backflow for types of water up to category 4.
For category 5 types of water an air gap separation must be used.


The table below, entitled “Protection matrix”, relates the categories of water to different types of system. It has been compiled on the basis of indications given by the European standard.


The European standard EN 12729 - “Devices to prevent pollution by backflow of potable water. Controllable backflow preventer with reduced pressure zone. Family B - Type A” - stipulates the functional, dimensional and mechanical requirements that must be met for controllable reduced pressure zone backflow preventers (BA type).

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