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Sprinkler K-factor is based on the following formula:

Q = Kp^{0.5}

Where:

Q – flow in gpm

K – nozzle discharge coefficient of K-factor for head in gpm/psi

P – pressure in psi

Q – flow in gpm

K – nozzle discharge coefficient of K-factor for head in gpm/psi

P – pressure in psi

The real meaning of K-factor is that the flow in gpm can be discharged from the nozzle when the pressure is 1 psi.

While K-factor is used in calculation in other units like that in SI system, the K-factor of a nozzle, such as a sprinkler, a measuring orifice, or even any outlet of a pipe, must be converted to a value based on the units of flow and pressure in such calculation.

The following table offers such conversions:

K-(gpm-psi) | K-(L/m-kPa) | K-(L/m-bar) | |||
---|---|---|---|---|---|

1 | gpm | 3.7854 | L/m | 3.7854 | L/m |

1 | psi | 6.8948 | kPa | 0.068948 | Bar |

1 | K-gpm/psi | 1.44 | K-L/m/kPa | 14.4 | K-L/m/bar |

In Hazen-Williams formula, flow is proportional to pressure to 1.85-th power, and thus K-factor is slightly different from that calculated by the above formula.

In flow testing and sprinkler system calculations using Hazen-Williams formula, K-factor is calculated using the following formula:

K = q/p^{0.54}

A K-factor calculated based on this formula is 45 times of the value calculated based on flow in L/s and pressure in kPa:

K = q/p^{0.54} = 1 gpm / (1 psi)^{0.54} = 0.0631 L/s / (6.895 kPa)^{0.54} = 0.0222

Therefore:

K-(L/s-kPa) = 0.0222 K-(gpm-psi)

or,
K-(gpm-psi) = 45 K-(L/s-kPa)

If bar is use for SI calculations, K-(L/s-bar) is 1/10 of K-(L/s-kPa), i.e. 4.5.