Source: TS EN 12845+A2:2026 (EN 12845:2015+A2:2026), Clauses 8.2, 10.2, 10.5, 10.6.2.1, 10.7 and Clause 20.3.4.2.
The sentence most often repeated in pump selection discussions, "70 % pressure at 140 % flow", does not exist in the text of TS EN 12845+A2:2026. The standard binds pump performance in three places and each of them does a different job: Table 16 gives the curve points for pre-calculated LH and OH, Table 14 says how the nominal flow is to be defined, and Figure 7 shows how the curve must cover the demand curve in calculated systems. This article separates the three.
Pre-calculated LH and OH: Table 16
Clause 10.7.1 (TSE p.65 / EN p.62): where pump sets take water from a storage tank, the pump set selected shall conform to the characteristics of pre-calculated LH and OH systems in accordance with Table 16.
In each row, Table 16 gives one set of nominal data and one or two characteristic points. In other words, the curve has to pass not through one point but through two or three. The whole table is given below (pressures are measured at the control valve set, Table 16 NOTE 1):
| Hazard class | h (height of sprinklers above the control valve set) | Nominal: bar / l/min | Characteristic 1: bar / l/min | Characteristic 2: bar / l/min |
|---|---|---|---|---|
| LH (wet or pre-action) | h ≤ 15 | 1.5 / 300 | 3.7 / 225 | - |
| LH (wet or pre-action) | 15 < h ≤ 30 | 1.8 / 340 | 5.2 / 225 | - |
| LH (wet or pre-action) | 30 < h ≤ 45 | 2.3 / 375 | 6.7 / 225 | - |
| OH1 wet or pre-action | h ≤ 15 | 1.2 / 900 | 2.2 / 540 | 2.5 / 375 |
| OH1 wet or pre-action | 15 < h ≤ 30 | 1.9 / 1 150 | 3.7 / 540 | 4.0 / 375 |
| OH1 wet or pre-action | 30 < h ≤ 45 | 2.7 / 1 360 | 5.2 / 540 | 5.5 / 375 |
| OH1 dry or alternate / OH2 wet or pre-action | h ≤ 15 | 1.4 / 1 750 | 2.5 / 1 000 | 2.9 / 725 |
| OH1 dry or alternate / OH2 wet or pre-action | 15 < h ≤ 30 | 2.0 / 2 050 | 4.0 / 1 000 | 4.4 / 725 |
| OH1 dry or alternate / OH2 wet or pre-action | 30 < h ≤ 45 | 2.6 / 2 350 | 5.5 / 1 000 | 5.9 / 725 |
| OH2 dry or alternate / OH3 wet or pre-action | h ≤ 15 | 1.4 / 2 250 | 2.9 / 1 350 | 3.2 / 1 100 |
| OH2 dry or alternate / OH3 wet or pre-action | 15 < h ≤ 30 | 2.0 / 2 700 | 4.4 / 1 350 | 4.7 / 1 100 |
| OH2 dry or alternate / OH3 wet or pre-action | 30 < h ≤ 45 | 2.5 / 3 100 | 5.9 / 1 350 | 6.2 / 1 100 |
| OH3 dry or alternate / OH4 wet or pre-action | h ≤ 15 | 1.9 / 2 650 | 3.0 / 2 100 | 3.5 / 1 800 |
| OH3 dry or alternate / OH4 wet or pre-action | 15 < h ≤ 30 | 2.4 / 3 050 | 4.5 / 2 100 | 5.0 / 1 800 |
| OH3 dry or alternate / OH4 wet or pre-action | 30 < h ≤ 45 | 3.0 / 3 350 | 6.0 / 2 100 | 6.5 / 1 800 |
The table has two notes. NOTE 1: the pressures shown are values measured at the control valve set or sets. NOTE 2: in buildings exceeding the heights shown, it shall be proven that the pump characteristics are adequate to provide the flows and pressures specified in 7.3.1.
There is a reading trap to watch for: the row labels of the table combine two classes. The row "OH2 dry or alternate / OH3 wet or pre-action" applies both to OH2 dry and to OH3 wet; OH3 dry is one row further down, with different values.
Nominal flow for HH and calculated systems: Table 14
Table 14 (within Clause 10.6.2.1, TSE p.62 / EN p.59) is headed "Pump pressure and flow value" and defines the flow at which the NPSH check is to be made:
| Pipework | Hazard class | Nominal pump flow | Pump inlet condition |
|---|---|---|---|
| Pre-calculated | LH / OH | Pressure and flow requirements from Table 6 | For tanks, the water supply at low water level (X in Figure 4) |
| Pre-calculated | HH | The pressure and 1.4 × the flow required from Table 7 | For booster pumps, at the minimum town main pressure |
| Fully calculated | All | The maximum pressure and flow required for the most favourable area | - |
This is the only factor of 1.4 in the standard, and it is not a rule about a point on the curve; it is a definition of the nominal flow. The same clause also gives the NPSH requirement: the suction pipework, including all valves and fittings, shall be designed so that at the maximum pump set flow shown in Table 14 and in accordance with EN 17451, the NPSH available at the pump inlet (calculated at the maximum anticipated water temperature) exceeds the NPSH required by at least 1 m.
Pre-calculated HHP and HHS: Clause 10.7.2
Clause 10.7.2 (TSE p.66 / EN p.63) is a single sentence: for pre-calculated HHP and HHS systems, the nominal pump set flow and pressure shall be in accordance with 7.3.2.
In other words, on the HH side the table that binds the pump is not Table 16 but Table 7 (TSE p.43 / EN p.40). Table 7 gives the maximum demand flow and the pressure at the highest design point (pd) according to the design density; for example, at a density of 10.0 mm/min the maximum demand flow in a wet or pre-action system is 3 050 l/min and in a dry or alternate system 3 800 l/min. Clause 7.3.2.1 defines the total control valve set pressure as the sum of three components: the pressure at the design point, the pressure equivalent of the height difference between the control valve set and the highest sprinkler downstream of the design point, and the pipe loss from the control valve set to the design point.
Calculated systems: Clause 10.7.3 and Figure 7
Clause 10.7.3 (TSE p.66 / EN p.63) is also a single sentence: the pump set shall be selected so as to meet the pressure and flow demand of the sprinkler system. See Figure 7.
Figure 7 is headed "Typical pump curve for a calculated system" and its key marks four points:
- most unfavourable area,
- design pump flow,
- maximum demand flow (Qmax),
- most favourable area.
The standard gives no safety margin percentage here. It is sufficient that the pump curve covers the demand of the most unfavourable area as well as that of the most favourable area. The importance of the most favourable area comes from Clause 13.2.3: the 6 m/s and 10 m/s velocity limits shall be satisfied for the steady flow condition of both the most favourable and the most unfavourable area of operation.
Where the town main is boosted, Clause 10.7.4 (TSE p.66 / EN p.63) requires an additional site test: it shall be demonstrated by a test that the unboosted supply provides the maximum demand flow plus 20 % at a pressure of at least 0.5 bar measured at the pump inlet, and this test shall be carried out at the time of maximum demand on the main.
Parallel pump arrangements: Clause 10.2
Clause 10.2 (TSE p.60 / EN p.57) contains four provisions:
- Pump sets shall have compatible characteristic curves and be able to operate in parallel at all possible flows.
- Where two pumps are installed, each shall be capable of providing the specified flows and pressures independently.
- Where three pumps are installed, each pump shall be capable of providing at least 50 % of the flow at the specified pressure.
- Where a superior single or duplicate water supply comprises more than one pump, no more than one of them shall be driven by an electric motor.
For ESFR systems, Annex P (TSE p.167 / EN p.164) additionally recommends: it is recommended that three 50 % pump sets in accordance with EN 17451 be used for the water supply of ESFR sprinkler systems.
Two hidden loads that distort the curve
Clause 10.5 (TSE p.61 / EN p.58): a continuous flow of water sufficient to prevent overheating shall be ensured while the pump is operating against a closed valve, and this flow shall be taken into account in the system hydraulic calculation and in the pump selection. Diesel engine cooling circuits usually use the same water; if additional water is used, it too shall be taken into account.
The pressure ceiling: Clause 8.2
Clause 8.2.1 (TSE p.45 / EN p.42): other than during testing, the water pressure shall not exceed 12 bar at the equipment connections and locations defined in 8.2.1.1 and 8.2.1.2. In pumped systems the increase in drive speed and pressure at the closed valve condition shall be taken into account.
- 8.2.1.1 lists, for all sprinkler systems: sprinklers, multiple jet controls, water flow detectors, dry pipe and pre-action alarm valves, accelerators and exhausters, water motor alarms, zone control valves.
- 8.2.1.2 additionally lists, for systems where the height difference between the highest and lowest sprinkler does not exceed 45 m: pump outlets (including the increase in speed at the closed valve condition), wet alarm valves, stop valves, mechanical pipe joints.
Clause 8.2.2 (TSE p.46 / EN p.43): in high rise sprinkler systems where the height difference exceeds 45 m, 12 bar may be exceeded at pump outlets and in risers and distribution pipes, provided that all equipment exposed to pressures greater than 12 bar is fit for purpose.
Starting behaviour, the nameplate and annual verification
- Clause 10.8.1.3 (TSE p.67 / EN p.64): the pump set shall run at its nominal capacity within 15 s of starting.
- Clause 18.2.5.1 (TSE p.119 / EN p.116): a plate shall be fixed to each suction or booster pump showing a) the outlet pressure in bar at the inlet condition and flow specified in Table 16, together with the corresponding nominal speed and flow in l/min, and b) the maximum power absorbed at any flow at the relevant speed.
- Clause 20.3.4.2.1 (TSE p.125 / EN p.122): in the annual routine each pump set shall be tested at full load conditions by means of the test line connection downstream of the pump outlet non-return valve and shall deliver the pressure and flow values stated on its nameplate. Appropriate allowances shall be made for pressure losses in the supply pipe and valves between the supply and each control valve set.
- Clause 8.5.1 (TSE p.47-48 / EN p.44-45): under f), at least three pressure/flow readings shall be taken to establish a test curve; in addition, the static pressure shall be read with no flow. Under e), pressure readings shall be taken only with a test gauge with an accuracy of ±1.6 %; under c), the error of the flow measuring device shall be within ±5 % of its maximum flow.
Frequently Asked Questions
How many points does EN 12845 define for the pump curve?
For pre-calculated LH and OH systems, Table 16 (Clause 10.7.1, TSE p.65 / EN p.62) gives one nominal point and one or two characteristic points for each hazard class and height range. For example OH3 wet or pre-action, h of 15 m and below: nominal 1.4 bar - 2 250 l/min; characteristic 2.9 bar - 1 350 l/min and 3.2 bar - 1 100 l/min.
Is there a rule in the standard saying 70 percent pressure at 140 percent flow?
There is no such provision in the text of TS EN 12845+A2:2026. The only factor of 1.4 in the standard is in Table 14 (Clause 10.6.2.1, TSE p.62 / EN p.59): for HH pipework the nominal pump flow is the pressure required from Table 7 and 1.4 times the required flow. This defines the maximum pump set flow at which the NPSH calculation is made.
How is the pump selected in calculated systems?
Clause 10.7.3 (TSE p.66 / EN p.63) is a single sentence: the pump set shall be selected so as to meet the pressure and flow demand of the sprinkler system; see Figure 7. The key to Figure 7 marks four points: most unfavourable area, design pump flow, maximum demand flow Qmax and most favourable area.
What capacity shall each pump have in a two or three pump arrangement?
Clause 10.2 (TSE p.60 / EN p.57): where two pumps are installed, each shall be capable of providing the specified flows and pressures independently. Where three pumps are installed, each pump shall be capable of providing at least 50 percent of the flow at the specified pressure.
What is the pressure limit at the pump outlet?
Clause 8.2.1 (TSE p.45 / EN p.42): other than during testing, the water pressure shall not exceed 12 bar at the points listed in 8.2.1.1 and 8.2.1.2, and in pumped systems the increase in speed and pressure at the closed valve condition shall be taken into account. In high rise buildings where the difference between the highest and lowest sprinkler exceeds 45 m, Clause 8.2.2 permits 12 bar to be exceeded at pump outlets and in risers.
References
- TS EN 12845+A2:2026 Clause 7.3.2.1, Table 7 (TSE p.43 / EN p.40)
- TS EN 12845+A2:2026 Clause 8.2.1 (TSE p.45 / EN p.42), Clause 8.2.2 (TSE p.46 / EN p.43)
- TS EN 12845+A2:2026 Clause 8.5.1 (TSE p.47-48 / EN p.44-45)
- TS EN 12845+A2:2026 Clause 10.2 (TSE p.60 / EN p.57)
- TS EN 12845+A2:2026 Clause 10.5 (TSE p.61 / EN p.58)
- TS EN 12845+A2:2026 Clause 10.6.2.1, Table 14 (TSE p.62 / EN p.59)
- TS EN 12845+A2:2026 Clause 10.7.1, Table 16 (TSE p.65 / EN p.62)
- TS EN 12845+A2:2026 Clauses 10.7.2, 10.7.3, 10.7.4, Figure 7 (TSE p.66 / EN p.63)
- TS EN 12845+A2:2026 Clause 10.8.1.3 (TSE p.67 / EN p.64)
- TS EN 12845+A2:2026 Clause 13.2.3 (TSE p.86 / EN p.83)
- TS EN 12845+A2:2026 Clause 18.2.5.1 (TSE p.119 / EN p.116)
- TS EN 12845+A2:2026 Clause 20.3.4.2.1 (TSE p.125 / EN p.122)
- TS EN 12845+A2:2026 Annex P, Clause P.1 (TSE p.167 / EN p.164)
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Download MEP Calc on the App StoreTS EN 12845+A2:2026 (EN 12845:2015+A2:2026) Fixed firefighting systems — Automatic sprinkler systems — Design, installation and maintenance; TS EN 12845-2:2025 (EN 12845-2:2024) ESFR and CMSA sprinkler systems. Every figure in this article is taken from the published standard text; clause, table and page references are listed under References. General information only, not a substitute for the standard or for a design review.