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Technical Information: Water Flow Characteristic


The friction loss in hydraulic can be evaluated through the use Of various flow coefficients. one such coefficient is the Hazen-Williams C factor. This factor for PVC & CPVC plastic piping system has been set at  at C=150. The following formulae express the friction loss in feet of water and the water velocities in feel per second.

Friction loss is based on Hazen-Williams formula  


F= friction head loss in feet of water per 100 feet of pipe
C= constant for inside pipe roughness (c=150 for extruded smooth wall thermoplastic pipe)
Q= flow in us gallons per minute
di= inside diameter of pipe in inches

The value of c 150 for thermoplastic pipe is based on engineering measurements made with new and used thermoplastic pipe in several laboratories. Thus the value of c = 150 has a conservative bias. Using c = 150 the equation reduces to

Water velocities in feet per second v may be calculated as follows

Typical values of the Hazen Williams coefficient

     Water Hammer_Pressure surge

Maximum pressure caused by water hammer May be calculated with the following formulae.


P = pressure surge (psi)
A = wave velocity (ftsec)
V = maximum velocity change (ftsec)
G = acceleration of gravity (32.2 ft sec2)
K= fluid bulk modulus (300 000 psi for water)
Di = pipe inside diameter (inches)
E = modulus of elasticity of the pipe (420 000 psi for PVC 360 000 psi for CPVC)
t = wall thickness (inches)


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