Inlet Manifolds for Fire Pumps: What Is Prohibited

Inlet manifolds for fire pumps: The answer depends on the hydraulic configuration (above-head or below-head) and the inlet conditions described in the sections cited in the referenced rules.*

The question: What is meant by “inlet manifolds”?

When we talk about “inlet manifolds,” we are essentially referring tothe interconnection of the inlet lines of multiple pumps that are connected to the same water supply.

This issue is not merely a matter of “plant engineering”: the choice affects the reliability and continuous operation of the pumps, especially under specific conditions where malfunctions may occur (as noted in the Inlet conditions).

UNI EN 12845: Overhead panels and prohibition on interconnection

In the case of an overhead installation, the text refers to the section on “inlet piping” and provides a clear instruction:

• Where more than one pump is installed, the inlet lines must not be interconnected.

In this configuration, therefore, the installation of inlet manifolds between main fire pumps is explicitly prohibited.

Overpressure: The jockey pump must be independent

That is not all: it is also specified that, if a pressure-maintaining (jockey) pump is installed in the upper tank, the inlet piping and its associated fittings and valves must be independent of those of the main pump(s).

The operational implication is clear: in the upper tank, in addition to the prohibition on manifold connections between the main pumps, the jockey pump must also have its own dedicated inlet, without sharing it with the main pumps.

UNI EN 12845: Underlayment and Interconnection Options (Subject to Conditions)

With regard to the provision on the lower hinge, the text below introduces an option:

• Where more than one pump is provided, the inlet lines may be interconnected if they are equipped with shut-off valves;
• The purpose is to allow each pump to continue operating when the other is taken offline for maintenance;
• The connections must be properly sized for the required flow rate.

Read at face value, the immediate conclusion would be: in summary, inlet manifolds for fire pumps can always be built. The text, however, clarifies that this is not the case.

Inlet Conditions: Why Interconnection Can Create Critical Issues

The chapter on inlet conditions highlights that water supply systems (both above-pipe and below-pipe) serving systems with deluge valves or dry hydrant networks require special attention during the overall design process.

Under certain operating conditions, malfunctions may occur that could result in:

• draining the pump;
• pump cavitation;
• phenomena related to exceeding the inlet capacity.

It is also noted that this phenomenon is particularly pronounced in the case of over-beam installations.

Sub-section: Examples of Problems with Inlet Interconnection

In the case described below, even if the interconnection were sized for the flow rates involved, the text points out potential problems in typical single-source supply scenarios, for example:

• 2 pumps, each operating at 100% capacity: simultaneous operation is not provided for under the regulations; the idle pump may be subject to air ingress through the interconnection (via devices and potential entry points such as minimum recirculation, diesel heat exchanger cooling, sealing devices, flanges, connections, shut-off valves, etc.);
• 3 pumps, each operating at 50% capacity: the system is designed for the simultaneous operation of two pumps; here as well, the idle pump may be subject to air ingress through the interconnection (with similar dynamics).

The key point is the principle stated: “superior” standalone power supplies, given their high degree of reliability, must not depend on interconnections that could cause problems stemming from the other interconnected pumps.

What this means: Prohibitions and Permitted Cases (according to the text)

When the passages cited are considered in sequence, the text leads to the following practical conclusions:

• It is expressly prohibited to install inlet manifolds above the floor slab where two or more pumps (including the jockey pump) are installed.
• Inlet manifolds are prohibited even in cases of individual water supplies with higher head (for technical reasons related to inlet conditions; this prohibition also applies to jockey pumps).
• Inlet collectors are eligible only in the case of single, underpressure feed systems, as stated in the final summary of the text.

Conclusion

Inlet manifolds for fire pumps are not a “standard” choice: the text in the footnote explicitly prohibits their use and requires that even the jockey pump be independent. In the lower section, interconnection may appear possible, but the inlet conditions and the issue of separate upper feed lines lead to a more restrictive approach, with interconnection permitted only in specific cases.