Our expert responds #21

QUESTION
I ask if you could go further into the topic of the use of submerged type pumps within UNI EN 12845

ANSWER
UNI EN 12845 10.6.1, allows the use of submerged pumps.

The standard puts some limits on their use, indicating that they should be fitted only if it is strictly necessary to do so, and asking for a technical justification for this choice.
Therefore, the report should indicate the reasons why the arrangements with the suction lift centrifugal pumps or with the VTPs could not be used.

We see some of the characteristics of systems that use submerged pumps, such as main fire-fighting pumps.
First of all, the hydraulic diagram that is created, is obviously the SUCTION LIFT one. So an ideal arrangement, for a safety system, like the one we're considering.
To minimise the loss of volume inside the tank, the pumps must be placed in a horizontal position.
To avoid overheating of the electric motor, the machines must be inserted into cooling hoods, built in such a way as to allow the entry of water, only from the rear part.
The water, lapping the motor, keeps it at a correct temperature.
The pipes that connect the pumps to the room are obviously under pressure. This allows one to place the fire-fighting water storage in a different place than the one chosen for the technical room.
This detail is very useful, when architectural or landscape constraints must be respected. In fact, it will be possible to bury the water storage in front of the prospectus, the view of which must not be impeded, and assemble the room in any place, even dozens of metres away from the water storage.
To obtain the sizing prevalence of the pumps, it will be sufficient to add to the design the prevalence of the network, the pressure drops between the pumps and the room.
As regards the characteristics of the room, reference should also be made to UNI/TR 11438:2016 point 7.1, where it is explicitly stated that the rooms, even with the use of submerged pumps, must comply with the requirements of UNI EN 12845:2020 and UNI 11292:2019.

So be mindful of the following:

• apart from the theme of the PUMP-SET, which in this case is not present, all the other requirements, contained in the aforementioned standards, including the minimum height, must be respected.

Finally, it should be noted that by using submerged pumps as main fire-fighting pumps, only SINGLE-TYPE WATER SUPPLIES can be made and never UPPER-TYPE WATER SUPPLIES.
This is because, of course, there is no possibility of connecting a diesel motor directly to the pump body, since the latter is mounted in water.
In order to obtain a higher level of reliability, not from the point of view of the standard, but from the functional point of view, the use of a generator unit as a security energy source has often been provided.

This is also to meet the requirements of the
Decree of the Interior Ministry of 20 December 2012, which provides that:

• in the absence of certification by the electricity grid operator, the professional shall independently certify the continuity and reliability required. Thus assuming an enormous responsibility from a civil and criminal point of view.
• The insertion of the generator unit greatly limits the possibility of out of service of the fire-fighting water supply, due to lack of electricity.

However, it must be clear that, even in the presence of a generator unit, the need remains to make a connection of the pump panels, which complies with the requirements, and which are highlighted in the figure.