What does this tool check?
The pump suction and starting rules of TS EN 12845+A2:2026 Section 10: suction pipe size and velocity, pump centre line position relative to the water level, NPSH margin, number of pumps, pressure-switch start pressures and the automatic priming tank under suction lift. It does not select a pump or check a pump curve.
What changed with A2: water supplies consisting of pumps conform to EN 17451 (Clause 10.1). Pump set characteristics, i.e. curve and rated-point requirements, were taken out of EN 12845 by A2 and left to EN 17451. EN 17451 is not available to us, so the tool does not check them.
Positive head or suction lift? (10.6.1)
Wherever possible, horizontal centrifugal pump sets are installed with a positive suction head. Both conditions apply together:
- at least two thirds of the effective capacity of the suction tank is above the pump centre line;
- the pump centre line is no more than 2 m above the low water level of the tank (level X in 9.3.5).
If these are not met, the arrangement is a suction lift.
Suction pipe (10.6.2.2 and 10.6.2.3)
| Condition | Minimum diameter | Maximum velocity | Further rule |
|---|---|---|---|
| Positive head | 65 mm | 1.8 m/s | Suction pipes may be interconnected only with stop valves so that each pump set keeps running when the other is removed |
| Suction lift | 80 mm | 1.5 m/s | Low water level to pump centre line ≤ 3.2 m; suction pipes not interconnected; foot valve at the lowest point |
The velocity is taken with the pump operating at maximum demand flow: v = Q / (π · d² / 4) The tool uses an approximate bore for steel pipe (sch 40) for each DN; the real bore depends on the pipe standard.
NPSH margin (10.6.2.1)
The suction piping, with all valves and fittings, is designed so that the available NPSH at the pump inlet (calculated at the maximum anticipated water temperature) exceeds the required NPSH by at least 1 m at the maximum pump set flow. Use the NPSH calculator to work out NPSHa from altitude, temperature and friction loss; NPSHr comes from the pump manufacturer.
Number of pumps (10.2)
- With two pumps, each one independently provides the specified flow and pressure (100 %).
- With three pumps, each one provides at least 50 % of the specified flow at the specified pressure.
- Where more than one pump is installed in a superior or duplicate water supply, no more than one is electrically driven.
Pressure switches (10.7.5)
Two pressure switches start each pump set; the sensing pipe is at least 15 mm and either switch starts the pump. The first pump starts before the trunk main pressure falls to 0.8 p; where two pump sets are installed, the second starts before it falls to 0.6 p, p being the closed-valve pressure. Once started, the pump runs until stopped manually.
Automatic priming (10.6.2.4, Table 15)
| Hazard class | Priming tank at least | Priming pipe at least |
|---|---|---|
| LH | 100 L | 25 mm |
| OH, HHP and HHS | 500 L | 50 mm |
If the water in the priming tank falls to 2/3 of its normal level, the pump starts, or an alarm is sent to a permanently attended location.
Frequently Asked Questions
What is the velocity limit in the suction pipe?
Under TS EN 12845+A2, with the pump at maximum demand flow, 1.8 m/s is not exceeded under positive head (Clause 10.6.2.2) and 1.5 m/s under suction lift (Clause 10.6.2.3). The minimum diameter is 65 mm under positive head and 80 mm under suction lift.
What counts as a positive suction head?
Clause 10.6.1: at least two thirds of the effective capacity of the suction tank is above the pump centre line and the centre line is no more than 2 m above the low water level. If both are not met, it is a suction lift, where the low water level to pump centre line distance is at most 3.2 m.
At what pressure must the pump start?
Clause 10.7.5: the first pump starts before the trunk main pressure falls to 0.8 p and, where two pump sets are installed, the second before it falls to 0.6 p, p being the closed-valve pressure. Each pump set has two pressure switches and runs until stopped manually.
Why are there no pump curve requirements?
TS EN 12845+A2 requires water supplies consisting of pumps to conform to EN 17451 (Clause 10.1), and pump set characteristics are left to that standard. EN 17451 is not available to us, so the tool does not check the pump curve.
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