Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

Head 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, 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.

$$\large{ h_{l-major} = f \; \frac{l}{d} \; \frac{v^2}{2\;g} }$$
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, abbreviated as $$h_{l-minor}$$, is the pressure drop caused by fittings and valves.

$$\large{ h_{l-minor} = K \; \frac{v^2}{2 \; g} }$$
$$\large{ h_{l-minor} }$$ = 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 $$\large{ \frac{ft}{sec} }$$   $$\large{ \frac{m}{s} }$$