Fire pump performance curve: yes/no 140%Q

Fire pump performance curve: Verification at the point where Q is 140% and H is 70% is not “always” mandatory. The answer depends on how the system is classified under UNI EN 12845.

In short: the “yes/no” answer (it depends on the type of system)

If the system is precalculated, the characteristic curve of the main pumps must also cover the point corresponding to 140% of Q, while maintaining 70% of H.

If the system is calculated in its entirety, this requirement is not stated in those terms; instead, the rules specify certain conditions related to the most favorable and least favorable areas and to performance during testing.

Applicable standard: UNI EN 12845 (sections 10.7.2 and 10.7.3)

The stated reference is UNI EN 12845, specifically:

• 10.7.2: Q/H characteristics of the main pumps for pre-calculated systems.
• 10.7.3: Q/H characteristics of the main pumps for the systems calculated in their entirety.

These two articles are not interchangeable: the standard defines different criteria depending on the design method used (precalculated vs. fully calculated).

Pre-calculated systems: when the curve must cover 140% of Q and 70% of H

For PRECALCULATED systems (and only for them), the rules require that:

1. The pump’s rated flow rate and pressure values must comply with Section 7.3.2 of UNI EN 12845, that is, they must be consistent with the design Q/H point derived from the tables in the standard.
2. The performance curve of the main pumps covers:

• the estimated design flow rate in Q/H, and
• as well as the point corresponding to 140% of Q, while maintaining 70% of H.

In other words: in the preliminary calculation, one does not limit oneself to the “table” operating point alone, but requires additional coverage of the curve at a point where the flow rate is higher.

Fully calculated systems: the requirements are different (inspection, areas, water reserve)

For FULLY CALCULATED systems, the requirement (Section 10.7.3) is phrased differently and focuses on specific performance checks:

• During testing at the manufacturer’s test facility, the pump must deliver a pressure that is 0.5 bar higher than that required forthe most unfavorable area.
• The pump must be capable of maintaining the Q/H operating point of the most favorable range even when the water level in the reservoir is at its lowest.

Therefore, as a general rule, we are not talking here about “always covering” 140% of Q with 70% of H: the regulation links this requirement to system conditions (favored/disadvantaged areas) and water supply conditions (minimum reserve level).

Why do the rules distinguish between pre-calculated and fully calculated?

The difference stems from the fact that:

• In the fully calculated scenario, the network is modeled in greater detail:the most favorable area andthe least favorable area (typically the area closest to the pump room and the one farthest away) are clearly identified. For this reason, the rules may require targeted checks:
  • pressure margin at the most unfavorable location (during testing),
  • Guarantee of the Q/H point in the most favorable area, even at the minimum water storage level.
• In the pre-calculated method, however, favorable and unfavorable areas are not identified: the tables lead to the identification of a single design Q/H point. Precisely for this reason, the standard “errs on the side of caution” and requires that the pump be capable of delivering performance that exceeds the point calculated using the tables, also mandating coverage of that point at 140% of Q with at least 70% of H.

How to Correctly Interpret the 140% Q / 70% H Rule

The rule is explained in the text as follows:

• The maximum flow rate to be observed: Q1 = Q × 1.4
• At that flow rate: H1 ≥ H × 0.7

This specification should be interpreted as a requirement based on the pump’s performance curve for the specific case considered, not as a “universal” guideline applicable to every system and every calculation method.

What to Check in Practice (Without Confusing the Two Cases)

To avoid errors in configuration or verification, it is best to clearly separate the checks:

• If the system is precalculated: verify that the fire pump performance curve covers both the design Q/H point and the point at 140% of Q while maintaining 70% of H.
• If the system is designed on a full-scale basis: verify the conditions required during testing (additional pressure relative to the most unfavorable area) and the ability to maintain the Q/H point of the most favorable area even when the water reserve is at its minimum level.

For a visual reference, the text refers readers to Figures 7a and 7b in Chapter 10 of UNI EN 12845.

Conclusion

The answer to the initial question is clear only after specifying the type of system: yes (precalculated) and no (fully calculated), because UNI EN 12845 establishes different criteria for verifying pump performance in the two approaches.

If you are unsure about which classification your system falls under and which tests to apply (the 140%/70% curve or testing under favorable/unfavorable conditions), it is advisable to establish a documentation and technical review process that complies with the standard.