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K-Factor Conversion

Sprinkler and other nozzles

Sprinkler K-factor is based on the following formula:

Q = Kp0.5
Where:
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-Factor Conversion (Based on q=K*P^0.5)
K-(gpm-psi)K-(L/m-kPa)K-(L/m-bar)
1gpm3.7854L/m3.7854L/m
1psi6.8948kPa0.068948Bar
1K-gpm/psi1.44K-L/m/kPa14.4 K-L/m/bar

K-Factor in Flow Test Using Hazen-Williams Formula

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/p0.54

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/p0.54 = 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.

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