EN 12845 Pump Performance Characteristics

The three classic problems that follow selecting a pump from a catalogue without checking the curve: overflow, cavitation and a burst alarm valve.

On a logistics warehouse project, a duty point of 4500 L/min at 6.5 bar was calculated for HHS3 protection. The consultant picked a pump from the manufacturer's catalogue that "met the duty point" and moved on. At commissioning two things failed at once: closed valve pressure shot to 11.8 bar, straining the alarm valve body seal, and at 140 % flow the pump pressure fell to 3.9 bar — unable to serve the hydraulics of the most favourable area. A single point had been selected and the rest of the curve never examined.

EN 12845 treats a pump not as a point but as a characteristic curve. Anyone who does not read the pump clause alongside the maximum pressure and cooling requirements ends up in the same scene. This article covers how the pressure-flow curve is checked under EN 12845, which points bind, and the errors most often made on site.

The relevant clauses

• Pump characteristics for LH and OH pre-calculated systems — a table giving a nominal point plus two further characteristic points.
• Pump characteristics for HHP and HHS pre-calculated systems — the pump must deliver at least 70 % of nominal pressure at 140 % of nominal flow.
• Calculated systems — the pump must exceed the most unfavourable area pressure by at least 0.5 bar and meet the most favourable area's flow and pressure at every water level.
• Maximum pressure — sprinkler equipment must not be exposed to more than 12 bar outside testing, so closed valve pressure is selected accordingly.
• Minimum continuous flow — the pump must not overheat running against a closed valve, so a continuous minimum flow (bypass) is included in the hydraulic calculation.

What the pressure-flow curve is, and what we look at

A centrifugal pump's flow-pressure curve rises steeply to the left and falls to the right. Three points bind:

1. Closed valve point (Q = 0): the pressure produced with all valves closed — the top left of the curve.
2. Duty point (Q_d, P_d): the flow and pressure the hydraulic calculation demands, where the pump curve crosses the system resistance curve.
3. 140 % flow point (1.4 × Q_d): where multiple sprinkler operation, the most favourable area or hose use pushes actual flow above duty. EN 12845 requires at least 0.7 × P_d here.

Demand flow versus pump flow

The hydraulic calculation gives you the system resistance curve — a parabola showing the pressure loss at a given flow. The pump curve is the manufacturer's test data. Where the two intersect is the actual duty point. Q_demand is what the calculation asks for; Q_pump is what the pump actually delivers in that system.

If the pump curve crosses the system curve far above it, the pump runs out toward excess flow: it operates at a point the calculation never anticipated, motor current rises, NPSH required grows and cavitation risk appears. Conversely, a curve with too little arc may meet the duty point but collapse dramatically at 140 %.

The three quantitative limits

1) 140 % flow at 70 % pressure minimum

This is the most binding pump rule in EN 12845. For HHP and HHS pre-calculated systems, the curve must pass above all three of:

• Q = 0 → P ≥ P_d
• Q = Q_d → P ≥ P_d
• Q = 1.4 × Q_d → P ≥ 0.7 × P_d

Anyone familiar with NFPA 20 should note the difference: NFPA 20 requires 65 % of rated pressure at 150 % flow; EN 12845 requires 70 % at 140 %. The numbers are close but not equivalent — decide on a European project using the NFPA limit and you will not get approval.

2) Closed valve pressure and the 12 bar limit

On a typical centrifugal pump, closed valve pressure runs to roughly 1.2–1.4 times the duty pressure. EN 12845 does not give that figure directly, but it does require that alarm valves, stop valves and mechanical connections are not exposed to more than 12 bar outside testing. On high-rise systems above 45 m the limit may be exceeded, but the equipment must then be selected for that pressure.

The practical check: closed valve pressure plus static head (the level difference between sprinkler and pump) plus any driver overspeed — a diesel governor can reach 110 % — must stay within 12 bar at the lowest equipment. If it does not, either select a flatter pump curve or fit a pressure reducing valve.

3) Continuous bypass at zero flow

The requirement is clear: to prevent the pump overheating against a closed valve, a continuous flow of water must be provided, and that flow must form part of the hydraulic calculation and pump selection. Manufacturers typically give it as a minimum continuous flow of 2–5 % of duty. The site solutions:

• An automatic recirculation valve from the pump discharge back to the suction tank.
• A fixed-orifice continuous bypass line.
• A separate test or bypass discharge with a visible outlet.

Without a bypass, a pump against a closed valve puts its energy into itself rather than the water; the gland cooks, excess vapour forms in a mechanical seal, and within minutes the rotor seizes. Teams who say "the pump ran, we held the pressure" at commissioning are called back a month or two later when the motor winding burns out.

Summary of the binding points

System type	Binding curve points
LH (wet or pre-action), h ≤ 15 m	Nominal 1.5 bar / 300 L/min; characteristic 3.7 bar / 225 L/min
OH1 (wet), h ≤ 15 m	Nominal 1.2 bar / 900 L/min; 2.2 bar / 540 L/min; 2.5 bar / 375 L/min
OH3 (wet), 30 < h ≤ 45 m	Nominal 2.5 bar / 3100 L/min; 5.9 bar / 1350 L/min; 6.2 bar / 1100 L/min
HHP1 to HHP3 and HHS	P(Qd) ≥ Pd; P(1.4 Qd) ≥ 0.7 Pd
Calculated systems	P at the most unfavourable area ≥ demand plus 0.5 bar; the most favourable area met at every water level
All systems — closed valve	Closed valve pressure at equipment ≤ 12 bar; continuous minimum bypass provided

Worked example — checking an HHS3 pump

Duty point: Q_d = 4500 L/min, P_d = 6.5 bar. The standard requires:

• At 140 % flow: at 1.4 × 4500 = 6300 L/min the pump must deliver at least 0.7 × 6.5 = 4.55 bar.
• Closed valve (Q = 0): a typical centrifugal gives P_closed ≈ 1.25 × P_d ≈ 8.1 bar. With 25 m of level difference between the pump discharge and the alarm valve on the lowest floor, the pressure there is 8.1 + 2.5 = 10.6 bar — within the 12 bar limit.
• Bypass: if the manufacturer gives a minimum continuous flow of 180 L/min, a 1 in orifice bypass line back to the suction tank is shown on the schematic.

Mark all three points on the manufacturer's curve. Where a point sits below the curve, the pump is acceptable; above it, the pump is eliminated.

Field error: not checking the curve

The three most common errors:

• Running out to excess flow: where the pump curve crosses the system curve too steeply, Q_pump far exceeds Q_demand. Motor current passes the nameplate, NPSH required rises, and cavitation begins at low water levels. The fix is a flatter pump characteristic or an orifice plate at the discharge to raise system resistance.
• Selecting on duty without checking 140 %: steeply falling curves meet the duty point but collapse at 1.4 Q_d, so discharge falls when the most favourable area opens. Rejection is close to guaranteed.
• Forgetting closed valve pressure and the bypass: alarm valve body cracks, gland fires and the classic "flange that burst in the first fire" all originate here.

Add to those the curve shift when two pumps run in parallel: two identical pumps do not double the flow. The system curve stays the same while the pump curve appears to shift right, but the real increase is 30–60 %. If one pump cannot meet the duty, two in parallel will not either — which is why the standard requires each pump in a parallel set to be capable of 100 % of the demand alone.

Comparison with NFPA 20

NFPA 20 does the same job with different numbers:

• NFPA 20: at least 65 % of rated pressure at 150 % flow; closed valve no more than 140 % of rated pressure.
• EN 12845: at least 70 % of rated pressure at 140 % flow for high hazard; closed valve bounded by the 12 bar equipment limit for systems below 45 m.

The NFPA "shut-off head no more than 1.4 × rated" rule has no direct EN 12845 equivalent, but the 12 bar equipment limit produces a similar practical outcome. On dual-approval projects, check both rules separately; the stricter binds.

Turkish context

BYKHY treats EN 12845 and NFPA 13 as equivalents for sprinkler design. On the pump side, NFPA 20 practice is more common in Turkey because pump manufacturers sell UL and FM listed sets certified to NFPA 20. Using an NFPA 20 listed pump on an EN 12845 project is not prohibited, but the performance points must be checked separately against the EN 12845 limits. Submissions that skip that difference come back for revision at fire service approval.

Frequently asked questions

What pressure must an EN 12845 pump deliver at 140 % flow?

At least 70 % of nominal pressure for HHP and HHS pre-calculated systems. A 6 bar duty pump must give at least 4.2 bar at 1.4 × Q.

Is there an upper limit on closed valve pressure?

Sprinkler equipment must not be exposed to more than 12 bar outside testing, so closed valve pressure must be kept within that limit. In high buildings the limit may be exceeded, but the equipment must be rated accordingly.

Why is a bypass needed at closed valve?

To prevent the pump overheating. A continuous minimum flow must be provided and included in the hydraulic calculation, typically through an automatic recirculation valve or a fixed-orifice bypass.

How is the pump curve selected in a calculated system?

The pump must exceed the most unfavourable area's required pressure by at least 0.5 bar and meet the most favourable area's flow and pressure at every water level — two bounding points, not one.

Can an NFPA 20 listed pump be used on an EN 12845 project?

Yes, but its curve must be checked separately against the EN 12845 140 %/70 % and 12 bar rules. The NFPA 150 %/65 % and shut-off limits are not equivalent.

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