Sprinkler K-Factor
The K-factor is a sprinkler head's discharge coefficient in the relation Q = K√P: flow equals K times the square root of pressure. It defines how much water a head delivers at a given pressure, anchoring every hydraulic calculation.
Why it matters on an MEPF project
Hydraulic design works backwards from required discharge density over the design area to the pressure each head needs — and the K-factor is the bridge. A design run for one K-factor, built with heads of another, silently delivers the wrong density: the calculations remain beautiful and the protection is fiction. Head schedules and procurement must match the calculation, model for model.
Higher-K heads deliver the same water at lower pressure — decisive in storage occupancies where high densities at workable pressures are the whole game. This is why racked warehouses gravitate to large-orifice heads: pushing high density through small-orifice heads demands pressures the pumps cannot sensibly provide.
How it's specified in practice
| Parameter | Typical / working position | Governing reference |
|---|---|---|
| Relation | Q = K√P (flow vs pressure at the head) | IS 15105 hydraulic basis |
| Standard orifice | General light/ordinary hazard coverage | IS 15105 selection |
| Large orifice / high-K | High-density demands (storage, high hazard) at practical pressures | IS 15105 selection |
| Design consequence | Head K must match the hydraulic calculation exactly | approved design |
Common mistakes
- Substituting "equivalent" heads at procurement with a different K than designed.
- Mixing K-factors within one design area.
- Reusing an old calculation after re-racking changed the hazard.
- Believing more pressure fixes an under-K'd system — the pump has limits and the mains have friction.
Related on this site
One of 68 working definitions in the MEPF & solar engineering glossary. The buying side of the same decisions is in the buyer's guides; the numbers are in the calculators.
Frequently asked
Where do I find a head's K-factor?
On the manufacturer datasheet and typically stamped on the head. The approved hydraulic calculation states the K it was designed for — the two must match on every head installed.
Does a bigger K-factor mean better protection?
It means more flow at a given pressure — the right choice where high density is required. "Better" is whatever matches the approved calculation; unmatched substitutions in either direction corrupt the design.
Standards referenced: IS 15105