Pressure-flow table for a K400 sprinkler. Every value is calculated from Q = K√P, with Q in litres per minute and P in bar.
Metric K400 corresponds to roughly K28.0 in imperial units (conversion factor 14.4). Typical application: ESFR; very high storage.
Pressure-flow table (K400)
| Pressure (bar) | Flow (L/min) | Flow (L/s) |
|---|---|---|
| 0.50 | 282.8 | 4.71 |
| 0.70 | 334.7 | 5.58 |
| 1.00 | 400.0 | 6.67 |
| 1.40 | 473.3 | 7.89 |
| 1.75 | 529.2 | 8.82 |
| 2.00 | 565.7 | 9.43 |
| 2.50 | 632.5 | 10.54 |
| 3.00 | 692.8 | 11.55 |
| 3.50 | 748.3 | 12.47 |
| 4.00 | 800.0 | 13.33 |
| 5.00 | 894.4 | 14.91 |
| 6.00 | 979.8 | 16.33 |
| 7.00 | 1058.3 | 17.64 |
| 8.00 | 1131.4 | 18.86 |
| 10.00 | 1264.9 | 21.08 |
| 12.00 | 1385.6 | 23.09 |
Required pressure at common design combinations
The table below shows the pressure a K400 sprinkler requires for a given density and coverage area. The calculation: required flow = density × coverage area; required pressure = (flow / K)².
| Density (mm/min) | Coverage area (m²) | Required flow (L/min) | Required pressure (bar) |
|---|---|---|---|
| 2.25 | 12.0 | 27.0 | 0.00 |
| 5.00 | 12.0 | 60.0 | 0.02 |
| 7.50 | 12.0 | 90.0 | 0.05 |
| 10.00 | 9.0 | 90.0 | 0.05 |
| 12.50 | 9.0 | 112.5 | 0.08 |
| 12.50 | 7.4 | 92.5 | 0.05 |
How to use it
- Take the design density (mm/min) from the hazard class.
- Find the coverage area (m²) from the sprinkler layout.
- Calculate the required flow by multiplying them.
- Read the required pressure from the table above, or calculate P = (Q/K)².
- Compare the result with the minimum sprinkler pressure the standard requires; if it is lower, use the minimum and recalculate the flow.
The table gives the pressure at the sprinkler inlet. In the hydraulic calculation, pipe friction loss, fitting equivalent lengths and elevation are added on top; the pressure at the system entry point is their sum.
Points to watch
- Confirm whether a catalogue K value is metric or imperial; the two differ by a factor of 14.4.
- For ESFR heads the K-factor comes with a minimum operating pressure defined in the listing; a table value does not mean you may go below that limit.
- A large K-factor works at low pressure but increases pipe diameter and water supply demand.
- A small K-factor produces finer droplets, weakening penetration into a stack in a storage fire.
Frequently Asked Questions
How much does a K400 sprinkler flow at 4 bar?
800.0 L/min from Q = K√P. That value corresponds to the pressure at the sprinkler inlet.
What is the imperial equivalent of metric K400?
Roughly K28.0. The conversion factor is 14.4, and which unit a catalogue uses must always be confirmed.
Can the sprinkler operate below a table value?
No. You cannot go below the minimum operating pressure defined in the product's approval document; for ESFR heads that limit is especially binding.
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Download MEP Calc on the App StoreNFPA 13 (2025) · BS EN 12845:2015+A1:2019 · EN 12259-1. Table values are calculated from Q = K√P; the manufacturer's approval document governs the product-specific minimum and maximum operating pressure.