The Hazen-William equation is an empirical one. It has a proportionality constant
that depends on the use of USCS units or SI units.
For the case of USCS units, pressure drop is in 'psig', length of pipe in 'ft', volume flow in 'gpm', and inside pipe diameter in 'in'.
For the case of SI units, pressure drop in 'm', length in 'm', volume flow in 'm3/s,
and inside pipe diameter in 'm'.
There are different ways of writing the hazen -william friction loss equation depending on which system of units you are working with. If you want to calculate friction loss in feet then the equation is as follows:hL = ((L)/(((6.27*10^-4)*C*D^2.63)^1.85))*Q^1.85Where:hL = Headloss (ft)L = Length of pipe (ft)C = Hazen William coefficient for the material that the pipe is made out of (unitless)D = Diameter of the pipe you are working with (in.)Q = Flow rate you are working with (cubic feet per second (cfs))
its not, the orifice headloss is higher because the change is abrupt.
A bend coefficient may be used for 1-D gradually varied flow and multiplied by the upstream cross-section averaged velocity head term, such that Headloss = C *a* u12/(2g) Where C is the bend coefficient which usually ranges between 0.05 - 0.6. The bend coefficient decreases as the radius of curvature decreases. a is the correction factor as a result of using cross-sectioned averaged velocity. This may be assumed as 1 if unknown, but is often times greater than 1 up to 1.4 u1 is the cross section averaged 1-D velocity for the upstream segment g is gravity