Having more main fire pumps means, first and foremost, complying with the specific requirements set forth in UNI EN 12845 (Section 10.2) when installing two or three main pumps. In this response, we clarify the rules, typical scenarios, and operational conclusions.
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Context: What does UNI EN 12845 (Section 10.2) say?
The applicable standard is UNI EN 12845, and specifically, Section 10.2 addresses systems with multiple pumps. There are four requirements to consider (in summary):
- The pumps must be capable of operating in parallel at all possible flow rates.
- If two pumps are installed, each must deliver 100% of the design flow rate at the design head.
- If three pumps are installed, each must be capable of delivering 50% of the required flow rate at the design head.
- When more than one pump is installed in a superior or dual-feed system, no more than one may be driven by an electric motor.
These four rules should be read together: they define both the required Hydraulic Performance and the constraints on motorization in certain scenarios.
Multiple Main Fire Pumps: General Requirements (UNI EN 12845)
The key point when discussing multiple pumps is their compatibility for parallel operation. It’s not enough to simply “install two (or three) pumps”; they must be able to work together at the flow rates specified for the system.
This leads to the following operational conclusion: to meet the parallel operation requirement, all main pumps must have the same Q/H characteristic curve.
In practice, the design of the pump group must be consistent from the outset: the selection of pumps is not independent, because parallel operation is an explicit requirement.
Parallel Operation: Why the Q/H Curve Must Match
The proposed summary is clear: to meet the requirement for parallel operation “at all possible flow rates,” the pumps must share the same Q/H curve.
This passage links directly to:
- the regulatory requirement (parallel operation);
- the technical choice (same characteristic curve).
If the curves are not consistent with one another, it becomes difficult (or uncontrollable) to ensure parallel operation within the intended operating range. For this reason, verification of the Q/H curve is treated as an enabling condition, not as a detail.
Installation with Two Pumps: What They Must Ensure
When TWO pumps are installed, the rule to follow is clear: each must deliver 100% of the design flow rate at the design head.
The operational conclusion, in the case of a single power supply, is as follows:
- Both pumps must each deliver 100% of the design flow rate;
- Both can be powered by an electric motor.
The following also remains true: there is no prohibition against using diesel-powered main pumps, so the use of diesel is possible in this scenario as well.
Installation with Three Pumps: What They Must Ensure
When THREE pumps are installed, the basic rule changes: each pump must be capable of delivering 50% of the required flow rate at the design head.
The practical conclusion, in the case of a single power supply, is:
- All three pumps must each deliver 50% of the design flow rate;
- All three can be powered by an electric motor.
The same note applies here: it is always possible to use diesel-powered main pumps, if deemed appropriate.
Single-channel vs. superior single-channel: What’s the Real Difference?
The most significant difference among the cases described is not in terms of flow rate or head (which remains as noted above for 2 or 3 pumps), but rather in the constraints related to the electric motor when moving to a higher “type” of power supply.
In the case of a single upper power supply, the following rule applies: only one pump can be driven by an electric motor.
This translates as follows:
- With two main pumps:
- Each one must provide 100% of the design flow rate;
- only one can be electric;
- The other one must be powered by a diesel engine.
- With three main pumps:
- Each one must provide 50% of the design flow rate;
- only one can be electric;
- The other two must be powered by diesel engines.
Furthermore, it is reiterated that there is nothing to prevent the use of only diesel-powered main pumps.
Electric Motors and Diesel Engines: Practical Rules (Without Ambiguity)
To summarize the above, the restrictions on engines depend on the type of fuel:
- Single power supply:
- with 2 pumps: both can be electric;
- with 3 pumps: all of them can be electric;
- However, the diesel fuel can still be used.
- Single top feed:
- In presence of multiple main pumps, only one can be electric;
- the rest must be diesel;
- You can also select the “all diesel” option.
This approach avoids the most common mistake: applying the constraint to the electric motor even when it is not required, or ignoring it when it is actually mandatory.
Quick Verification Checklist (Operational Checklist)
Before considering the issue “resolved,” verify that the installation consistently complies with the following points:
- The pumps are designed to operate in parallel at the expected flow rates.
- The main pumps have the same Q/H characteristic curve.
- With 2 pumps: each delivers 100% of the design flow rate at the design head.
- With 3 pumps: each provides 50% of the required flow rate at the design head.
- If the power supply is single-phase: only one pump can be powered by an electric motor.
- The use of a diesel engine is permitted and, in certain cases, is required for one or more pumps.
Conclusion
Systems with multiple main fire pumps can only be configured correctly if the following factors are considered together: parallel operation (and thus consistency of the Q/H curve), the required performance for 2 or 3 pumps (100% or 50% at design head), and motor constraints in cases of a single, higher-rated power supply.
