# Velocity Head

## Dynamic pressure and velocity head

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Dynamic pressure in a fluid flow can be expressed as

*p _{d} = ρ_{f} v*

^{2 }

*/ 2 (1)*

*where *

*p _{d} = dynamic pressure in fluid (Pa, psf (lb/ft^{2}))*

*ρ _{f} = density of fluid (kg/m^{3}, lb/ft^{3})*

*v = fluid velocity (m/s, ft/s)*

*1 Pa = 10*^{-6}N/mm^{2}= 10^{-5}bar = 0.1020 kp/m^{2}= 1.02x10^{-4}m H_{2}O = 9.869x10^{-6}atm = 1.45x10^{-4}psi (lbf/in^{2})*1 psf (lb*_{f}/ft^{2}) = 47.88 N/m^{2}(Pa) = 0.006944 lb_{f}/in^{2}(psi)

Head water column can be calculated by dividing dynamic pressure with specific weight of water like

*h _{w} = p*

_{d }

*/*

*γ*

_{w}

* = (ρ_{f} v^{2}/2) / ρ_{w} g *

* = v^{2}/ 2 g (2)*

*where*

*h _{w} = head water (m Water, ft Water)*

*γ _{w}*

*=*

*ρ*_{w}g*= specific weight water (*

*N/m*, l^{3}*b/ft*)^{3}*where *

* ρ_{w }= density of water (kg/m^{3}, lb/ft^{3})*

*g = acceleration of gravity (32.174 ft/s ^{2}, 9.81 m/s^{2})*

### Air Flow - Velocity and Dynamic Head Chart

Charts are based on air density *1.205 kg/m*^{3}* *and water density *1000 kg/m*^{3}.

### Water Flow - Velocity and Dynamic Head Chart

### Velocity Heads

Velocity - v -(ft/sec) | Velocity Head - v^{2}/2g -(ft Water) |

0.5 | 0.004 |

1.0 | 0.016 |

1.5 | 0035 |

2.0 | 0.062 |

2.5 | 0.097 |

3.0 | 0.140 |

3.5 | 0.190 |

4.0 | 0.248 |

4.5 | 0.314 |

5.0 | 0.389 |

5.5 | 0.470 |

6.0 | 0.560 |

6.5 | 0.657 |

7.0 | 0.762 |

7.5 | 0.875 |

8.0 | 0.995 |

8.5 | 1.123 |

9.0 | 1.259 |

9.5 | 1.403 |

10.0 | 1.555 |

11.0 | 1.881 |

12.0 | 2.239 |

13.0 | 2.627 |

14.0 | 3.047 |

15.0 | 3.498 |

16.0 | 3.980 |

17.0 | 4.493 |

18.0 | 5.037 |

19.0 | 5.613 |

20.0 | 6.219 |

21.0 | 6.856 |

22.0 | 7.525 |

*1 ft (foot) = 0.3048 m = 12 inches = 0.3333 yd*

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