Our expert responds #23

QUESTION
If you would kindly like to specify what is meant by overpressure system, and if this system is still usable pursuant to UNI EN 12845

ANSWER
The UNI EN 12845 edition of 2007, reported in points 8.6.3 and 9.2.2 the necessary indications for the design and implementation of this type of fire-fighting water supply.

These are, as can be seen from the figure, of one or more centrifugal pumps (see 9.2.2), placed directly in suction on the aqueduct pipe.
If there is only one pump, once again point 9.2.2. tells us that it is necessary to provide a by-pass, to be carried out as shown in the figure.
In addition, it is necessary to be in possession of an authorisation from the supplying entity (the aqueduct’s operator). This request is fundamental, because in this type of application, there is the possibility of putting the pipeline of the aqueduct in depression. If, as almost always happens in Italy, it is the piping of an aqueduct for drinking water use, one runs the risk that sewage from outside could enter into the pipeline (in the pipeline, there is a lower pressure than atmospheric pressure). The consequence of this would be a dangerous pollution of the water resource, with the related risks to public health.
Remember that the connection of a suction pump on an aqueduct pipeline is normally prohibited (strictly) for the reason we have explained. Therefore, connecting without authorisation becomes not only an administrative offence, but also a criminal offence because public health is put at risk.

The subsequent editions of UNI EN 12845, in particular that of 2015 and 2020, eliminated point 9.2.2 and retained only, in point 9.2, a note, which recalls the need to request authorisation from the operating authority, for any connection to be made on the piping of an aqueduct.
Point 8.6.3. has remained unchanged, where the possibility of using the overpressure pump is still mentioned.

So in summary:

• Overpressure pumps are allowed
• For connection to the aqueduct, an authorisation from the operating authority is essential
• This connection, carried out on a resource of drinking water, even if authorised, remains a risk from the point of view of public health
• If the connection were to be made on an industrial or fire-fighting aqueduct, the problem of pollution would be greatly reduced

Personally, I would never dream of creating a system of this type, on an aqueduct for drinking water.