EN 12845 Pump Suction Conditions and Pump Room Layout

The geometry of the pump room and the suction chamber is covered in two separate places in EN 12845: the geometry of the storage tank suction inlet in Clause 9.3.5 (Figure 4 and Table 12), and the pump compartment itself in Clause 10.3. Confusing these two clauses is the most common mistake on site: the dimensions in Table 12 are not wall distances. Source: TS EN 12845+A2:2026, Clause 9.3.5 and Clause 10.3, EN p.50-51 and EN p.57-58.

Figure 4 and Table 12: suction inlet distances

Clause 9.3.5 (EN p.50) defines how the effective capacity of storage tanks is calculated in accordance with Figure 4 and gives the following symbols:

• N: normal water level;
• X: low water level;
• d: nominal size of the suction pipe.

Table 12 specifies two minimum dimensions:

• A: the minimum distance from the suction pipe to the low water level (see Figure 4);
• B: the minimum distance from the suction pipe to the bottom of the sump (see Figure 4).

Figure 4 shows two cases: without a sump (1) and with a sump (2). A tank may be provided with a sump in order to maximize the effective capacity. The standard gives no dimension for the distance from the suction inlet to the nearest wall.

Table 12: Suction pipe inlet openings (EN p.51)

Clause 9.3.5 (EN p.51): if a vortex inhibitor of the minimum dimensions specified in Table 12 is fitted, dimension A may be reduced to 0.10 m.

All values in the table are absolute dimensions. The standard gives no proportional rule of the form "so many times the diameter" (for example 0.5d, 1d, 2d or 8d). When reviewing a design, the dimensions should be read directly from this table.

Tank capacity and filling

• Clause 9.3.2.1 (EN p.47): the effective capacity of the tank is calculated by taking the difference between the normal water level and the lowest effective water level. Where the tank is not protected against frost, the normal water level is raised by at least 1.0 m and ice venting is provided. Ready access is provided for covered tanks. Except for open reservoirs, tanks are provided with a water level indicator that can be read from outside.
• Clause 9.3.3 (EN p.48): the water supply shall be able to fill the tank in not more than 36 hours. The outlet of any filling pipe is at least 2.0 m horizontally from the inlet of the suction pipe.
• Clause 9.3.4 (EN p.48): for reduced capacity tanks the inlet is from the town main and automatic, provided through at least two mechanical ball float valves, does not adversely affect the pump set suction, and the failure of a single ball float valve does not impair the required filling rate.

Inexhaustible supplies: settling and suction chambers

Clause 9.4 (EN p.51-52) covers settling or suction chambers fed from an inexhaustible supply and refers to Figure 5 and Table 13. The principal provisions defined in this clause are:

• Pipes, channels and the beds of open channels have a continuous fall of at least 1:125 towards the settling or suction chamber.
• In flowing water, the angle between the direction of flow and the axis of the suction (looking in the direction of flow) is less than 60°.
• The inlet of the pipe or channel is submerged at least one nominal pipe diameter below the lowest known water level.
• The dimensions of the suction chamber, the position of the suction pipes relative to the chamber walls, the submergence below the lowest known water level and the clearance from the bottom conform to 9.3.5 together with Figures 4 and 5.
• The settling chamber is of the same width and depth as the suction chamber; its length is at least 10d, where d is the minimum internal diameter of the pipe or channel, and not less than 1.5 m.
• The system is designed so that the mean water velocity does not exceed 0.2 m/s at any point between the inlet of the settling chamber and the inlet of the pump set suction pipe.
• The settling chamber is arranged, including by screened arrangements, so as to prevent the entry of wind blown debris and sunlight.
• Before entering the settling chamber, the water passes through a screen of removable wire mesh or perforated metal sheet with a total open area below the water level of 150 mm² for every l/min of the rated pump set flow in LH or OH and of the maximum design flow in HHP or HHS. The screen mesh is not larger than 12.5 mm and two screens are provided, one in use and the other raised ready for replacement for cleaning.
• A strainer with a total open area of at least five times the cross sectional area of the pipe or channel is fitted at the inlet of the pipe or channel feeding the settling chamber or the suction pit; individual openings are sized so as to prevent the passage of a sphere 25 mm in diameter.

Table 13: Nominal size of the feed pipe for settling and suction chambers (EN p.53)

For sizes not in the table, the standard proposes the following relationship: d ≥ 21.68 Q^0.357.

Clause 10.3: compartments for pump sets

Clause 10.9.1 (EN p.65) repeats the same point from the diesel side: sufficient fresh air shall be available in the pump room at all times to keep the diesel pump set operating within the limits stated by the manufacturer and within EN 17451.

The standard gives no m³/h or air flow per unit of engine power for pump room ventilation; it specifies no fire class for the door (for example EI 60); and it sets no upper ambient temperature limit. These three items are resolved with supplier data and local legislation.

Water temperature: Clause 10.4

The water supply temperature does not exceed 40 °C. Where submersible pump sets are used, the water temperature does not exceed 25 °C unless the suitability of the motor for temperatures up to 40 °C is demonstrated (EN p.58).

Deciding the suction regime: summary

Field note: since column A of Table 12 gives the submergence depth and column B the bottom clearance, bringing the suction inlet close to a wall inside a tank is not in itself a direct breach of the standard; however, the risk of vortex and pre-rotation is a hydraulic design matter, and the use of a vortex inhibitor is already anticipated by Table 12's own column.

Frequently Asked Questions

What do dimensions A and B in Table 12 represent?

TS EN 12845+A2:2026 Clause 9.3.5 and Figure 4 (EN p.50-51): A is the minimum distance from the suction pipe to the low water level and B is the minimum distance from the suction pipe to the bottom of the sump. Neither is a distance to a wall; the standard gives no dimension for the distance from the suction inlet to a wall. For example, for a DN100 suction pipe without a vortex inhibitor, A is at least 0.37 m and B at least 0.10 m.

What does dimension A become when a vortex inhibitor is used?

Clause 9.3.5 (EN p.51): if a vortex inhibitor of the minimum dimensions specified in Table 12 is fitted, dimension A may be reduced to 0.10 m. Table 12 also gives the minimum size of the vortex inhibitor for each diameter: 0.20 m for DN65 and DN80, 0.40 m for DN100, 0.60 m for DN150, 0.80 m for DN200, 1.00 m for DN250, and 1.20 m for DN300, DN400 and DN500.

What fire resistance shall the pump room have?

Clause 10.3.1 (EN p.57): pump sets are located in a compartment with at least 60 minutes fire resistance that is not used for any purpose other than fire protection. In order of preference: a) a separate building, b) a building adjoining the sprinkler protected building with direct access from outside, c) a compartment inside the sprinkler protected building with direct access from outside. The standard does not specify a class for the door (for example EI 60).

At what temperature is the pump room maintained?

Clause 10.3.3 (EN p.58): the pump set compartment is maintained at a minimum of 4 °C for electric driven pump sets and 10 °C for diesel driven pump sets. The standard gives no upper temperature limit. Clause 10.4 limits only the temperature of the water: the water supply temperature does not exceed 40 °C, and 25 °C for submersible pump sets unless the suitability of the motor is demonstrated.

Must the pump room be protected by sprinklers?

Yes. Clause 10.3.2 (EN p.58): compartments for pump sets shall be sprinkler protected. Where the compartment is detached, the protection may be provided from the nearest accessible point downstream of the pump outlet check valve, by means of a subsidiary stop valve secured in the open position and a water flow detector conforming to EN 12259-5. A drain and test valve of 15 mm nominal size is fitted downstream of the flow alarm so that the alarm system can be tested practically.

References

• TS EN 12845+A2:2026 Clause 9.3.2.1 (EN p.47)
• TS EN 12845+A2:2026 Clauses 9.3.3, 9.3.4 (EN p.48)
• TS EN 12845+A2:2026 Clause 9.3.5, Figure 4 (EN p.50)
• TS EN 12845+A2:2026 Table 12, Clauses 9.3.6, 9.4.1 (EN p.51)
• TS EN 12845+A2:2026 Figure 5, Clauses 9.4.2 - 9.4.5, Table 13 (EN p.52-53)
• TS EN 12845+A2:2026 Clause 10.3.1 (EN p.57)
• TS EN 12845+A2:2026 Clauses 10.3.2, 10.3.3, 10.3.4, 10.4 (EN p.58)
• TS EN 12845+A2:2026 Clauses 10.6.1, 10.6.2.1 (EN p.59)
• TS EN 12845+A2:2026 Clause 10.6.2.3 (EN p.60)
• TS EN 12845+A2:2026 Clause 10.9.1 (EN p.65)

SprinkCalc — Fire Sprinkler Design Across Three Standards

SprinkCalc covers hazard classification, design density and area, K-factor selection, water demand and hydraulic calculations for NFPA 13, FM Global and BS EN 12845 in a single iOS app, and exports a professional PDF report.

Download SprinkCalc on the App Store

MEP Calc — 86+ Engineering Calculators

MEP Calc bundles 86+ engineering modules in one iOS app: 21 fire calculations plus heating, cooling, HVAC, plumbing, steam and natural gas.

Download MEP Calc on the App Store