Our expert responds #19

QUESTION
I would like you to explain to us once and for all what types of pumps can be used for fire-fighting water supplies.

ANSWER
The standard to refer to, when it comes to pumps that can be used to supply fire-fighting networks, is of course UNI EN 12845: 2020, in particular in point 10.6.1 and in the App. E

In addition to it, reference should also be made to T/R 11438:2016 point 8.4
Therefore, going in order:
The types that can be used are:
Point 10.6.1 UNI EN 12845

• Horizontal axis centrifugal pumps
• Submerged Vertical axial flow pumps (VTP)
• Submerged pumps

Appendix E UNI EN 12845

• Horizontal multistage pumps

Point 8.4 T/R 11438

• Axial split case pumps

With regard to the hydraulic arrangement, the SUCTION LIFT type is obviously preferred.
Therefore, going in order, the machines to be preferred are the Horizontal axis centrifugal pumps in the suction lift hydraulic arrangement

On the same reliability level, UNI EN 12845, puts the Vertical axial flow pumps (VTP) which are, of course, SUCTION LIFT

The great advantage of this arrangement, compared to the one with the centrifugal pumps, is linked to the fact that the water supply storage tank is moved below the level of the ground floor. Outside, therefore, the only volume involved is that of the water plant room.
The same result would also be achieved using horizontal centrifugal pumps, with a POSITIVE HEAD hydraulic arrangement, a version that the standard admits, only if one has not been able to use the two previous SUCTION LIFT arrangements.
This is because the POSITIVE HEAD condition is the source of a thousand problems (see this link)

With the diagrams we have seen so far, it is possible to create both single-type water supplies, and single-type upper water supplies. In fact, it is possible in both cases to couple both electric and diesel motors to the main pumps.

UNI EN 12845 also calls for the use of submerged pumps, only if strictly necessary and as usual asks to justify this choice. Indicating, in the report, why the arrangements with the centrifugal pumps or with the VTPs could not be used.

Horizontal multistage pumps are only dedicated to the so-called "High Vertical Development" systems – Appendix E already mentioned. Where the prevalence to be obtained is such that the use of this type of machine is necessary.
Finally, "axial split cases" are machines dedicated to particular uses, where the flow rates of horizontal centrifugal pumps usually do not arrive.