Question

You have a 12-inch PVC water main that is 850 feet long flowing at 5.6 cfs. Point A is at an elevation of 750 ft. Point B is at an elevation of 765 ft. If the pressure in a water main at Point A is 85 psi, what is the pressure at point B, in psi? (5 points)

Answer 1

Known :

D = 12 in = 1 ft

L = 850 ft

Q = 5.6 cfs

hA = 750 ft

hB = 765 ft

PA = 85 psi = 12240 lb/ft²

Solution :

A = πD² / 4 = π(1²) / 4

A = 0.785 ft²

Velocity of water :

U = Q / A = 5.6 / 0.785

U = 7.134 ft/s

Friction loss due to pipe length :

Re = UD / v = (7.134)(1) / (0.511 × 10^(-5))

Re = 1.4 × 10⁶

(From Moody Chart, We Get f = 0.015)

hf = f(L / d)(U² / 2g) = 0.015(850 / 1)((7.134²) / 2(32.2))

hf = 10 ft

PA + γhA = PB + γhB + γhf

PB = PA + γ(hA - hB - hf)

PB = 12240 + (62.4)(750 - 765 - 10)

PB = 10680 lb/ft²

PB = 74.167 psi