Hydrant Rated Flow at 20 psi (NFPA 291)
Hydrant rated capacity at 20 psi residual.
Example
You enter
- Static pressure (psi) 70
- Residual pressure while flowing (psi) 50
- Test flow QF (gpm) 1000
You get
- Rated flow at 20 psi 1640
Checked against published worked examples from: City of Temecula Fire Prevention Bureau.
Details, formula, and sources
ScopeQR = QF (hr/hf)^0.54, hf = static - residual, hr = static - 20, with the AA/A/B/C color class. Static 70, residual 50, QF 1000 gpm -> 1640 gpm, Class AA; static 65, residual 45, QF 800 -> 1240 gpm, Class A. A field/planning estimate; the water authority's data govern.
Formula or tablehf = static - residual; hr = static - 20; QR = QF (hr/hf)^0.54; class AA/A/B/C by QR.
Source and editionThe NFPA 291 hydrant rated-flow-at-20-psi projection and the color-class marking, by name.
Free accessThe QR = QF (hr/hf)^0.54 flow projection and the AA/A/B/C color classes are the published NFPA 291 method.
What governsEstimate. AHJ and licensed professional govern.
API field namesstatic_psi, residual_psi, qf_gpm, qr_gpm
- Flow projection QR = QF (hr/hf)^0.54, hf = static - residual, hr = static - 20NFPA 291
- Color class AA >= 1500, A >= 1000, B >= 500, C < 500 gpmNFPA 291
- Single test one location and time; the water authority's data governscope of this tile