Head Loss

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

hydraulic head lossHead loss, abbreviated as \(h_l\), is a pressure loss due to the resistance of the fluid and obstructions along the way in a pipe.  There are a number of factors that affect head loss such as:

  • flow rate
  • corrosion and scale deposits
  • fittings (bends, elbows, exits, expanders and reducers, tees)
  • inside diameter of the pipe
  • roughness of the pipe wall
  • viscosity of the liquid
  • length of the pipe
  • straightness of the pipe
  • valves


Major Head Loss

Major head loss, abbreviated as \(h_{l-major}\), is the pressure drop caused by friction loss.  It does not matter if the pipe is horizontal, vertical or on an incline.

Major Head Loss Formula

\(\large{ h_{l-major} = f \; \frac{l}{d} \; \frac{v^2}{2\;g}  }\) 
Symbol English Metric
\(\large{ h_{l-major} }\) = major head loss  \(\large{ ft }\)  \(\large{ m }\)
\(\large{ f }\) = friction factor \(\large{ dimensionless }\)
\(\large{ g }\) = gravitational constant \(\large{\frac{lbf-ft^2}{lbm^2}}\)  \(\large{\frac{N - m^2}{kg^2}}\) 
\(\large{ l }\) = lenght of pipe \(\large{ ft }\)  \(\large{ m }\)
\(\large{ d }\) = pipe inside diameter \(\large{ in }\)  \(\large{ mm }\)
\(\large{ v }\) = velocity of flow \(\large{ \frac{ft}{sec} }\) \(\large{ \frac{m}{s} }\)


Minor Head Loss

Minor head loss, abbreviated as \(h_{l-minor}\), is the pressure drop caused by fittings and valves.

Minor Head Loss Formula

\(\large{ h_{l-minor} = K \; \frac{v^2}{2 \; g}  }\) 
Symbol English Metric
\(\large{ h_{l-minor} }\) = minor head loss  \(\large{ft}\)  \(\large{m}\)
\(\large{ g }\) = gravitational constant \(\large{\frac{lbf-ft^2}{lbm^2}}\)  \(\large{\frac{N - m^2}{kg^2}}\) 
\(\large{ K }\) = loss coefficient \(\large{ dimensionless }\)
\(\large{ v }\) = velocity of flow \(\large{ \frac{ft}{sec} }\)   \(\large{ \frac{m}{s} }\)


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Tags: Hydraulic Equations Head Equations