K Factor
The sprinkler constant as given by the manufacturer. If left blank in the data for Sprinkler/Nozzles on the Discharge Tab Page, the program assumes the default above the column heading. k is the ratio of the sprinkler discharge divided by the square root of the pressure drop of the sprinkler or nozzle.
i.e. k = Q /√ P
The sprinkler constant entered must be consistent with the units of flow and pressure specified in the Project Tab Page.
The following table lists typical values of k for various sprinklers:
| Sprinkler Orifice Size mm (ins) | Sprinkler constant k with units of flow and pressure of: | |||
|---|---|---|---|---|
| l/min & kPa | l/sec & kPa | USGPM & PSI | L/min & Bar | |
| Commercial | ||||
| 10 (3/8) | 5.70 | 0.095 | 4.0 | 57.0 |
| 15 (1/2) | 8.00 | 0.133 | 5.6 | 80.0 |
| 20 (3/4) | 11.50 | 0.192 | 8.0 | 115.0 |
| Domestic | ||||
| 9.5 (3/8) | 4.00 | 0.067 | 2.8 | 40.0 |
| 11.1 (7/16) | 6.00 | 0.100 | 4.2 | 60.0 |
| 12.7 (½) | 8.00 | 0.133 | 5.6 | 80.0 |
| 13.5 (17/32) | 11.70 | 0.195 | 8.1 | 117.0 |
The following table lists typical values of k and the pressure exponent for various atomizer nozzles.
| Nozzle Type | Constant k with units of flow and pressure of: | Pressure Exponent | |||
|---|---|---|---|---|---|
| l/min & kPa | l/sec & kPa | USGPM & PSI | L/min & Bar | ||
| Swirl Type | 0.10 | 0.0017 | 0.069 | 0.995 | 0.5 |
| Cluster Swirl Type | 0.11 | 0.0018 | 0.073 | 1.05 | 0.5 |
| Spiral | 1.37 | 0.023 | 0.95 | 13.7 | 0.5 |
| Full Cone | 1.65 | 0.027 | 1.08 | 14.4 | 0.47 |
| Wide Angle Full Cone | 1.60 | 0.027 | 0.99 | 12.5 | 0.44 |
The following table lists typical values of k for various nozzles.
| NozzleSize mm(ins) | Constant k with units and flow and pressure of: | ||||
|---|---|---|---|---|---|
| Coeff. of dis-charge | l/min & kPa | l/sec & kPa | USGPM & PSI | L/min & Bar | |
| 6 (1/4) | 2.1 | 0.035 | 1.46 | 21.0 | |
| 8 (5/16) | 3.0 | 0.050 | 2.10 | 30.0 | |
| 10 (3/8) | 4.3 | 0.071 | 3.01 | 43.0 | |
| 12 (1/2) | 0.985 | 9.5 | 0.158 | 6.65 | 95.0 |
| 16 (5/8) | 0.985 | 16.9 | 0.282 | 11.8 | 169.0 |
| 19 (3/4) | 0.983 | 23.8 | 0.396 | 16.7 | 238.0 |
| 22 (7/8) | 0.982 | 31.8 | 0.531 | 22.3 | 318.0 |
| 25 (1) | 0.972 | 40.7 | 0.678 | 28.5 | 407.0 |
| 28 (1 1/8) | 0.976 | 51.3 | 0.854 | 35.9 | 513.0 |
The values for 6, 8 and 10 mm nozzles are typical values while for larger sizes the discharge through the nozzle is expressed (in AS 2419-1980 Installation of Fire Hydrants) in terms of a coefficient of discharge Cd for use in the formula -
Q = Cd.A..√ (2gh)
where:
Q = discharge in cubic metres per second.
Cd = coefficient of discharge.
A = area of nozzle of diameter d in sq. metres.
g = acceleration due to gravity in metres per second squared.
h = hydraulic head just before the nozzle in metres.
The flow through a sprinkler is given by -P
Q = k √ P
where:
Q = flow in litres per minute.
P = pressure in kilopascals.
The equivalent k value for nozzles is therefore, by combining these two equations.
k = 0.067 C<sub>d</sub>d 2
where:
d = nozzle diameter in mm, and k is in units of l/min and kPa