The fire department needs information on friction losses occurring between a water main and an open fire hydrant. at maximum main pressure (85 psig), the water discharge rate is 1620 gpm through a 2.5-inch open fire hydrant. the water main, in which the velocity is very small, is situated 8 ft below the hydrant discharge point. determine the friction loss from the main to the discharge point. assume atmospheric pressure is 15 psia.

Explanation:

The given data is as follows.

      = 85 psig,   = = 15 psia

        Q = 1620 gpm,  d = 2.5 inch,     l = 8 ft = 2.4384 m

According to Darey-Weisbach equation,

                         ......... (1)

Value of 'f' will be decided on the basis of Reynold number.

As, it is known that

where,   = kg/ms

As it is known that 1 gpm =

So,   = 3.67 gpm

Therefore,   Q =

                        =

                         = 0.1226

In, 1 inch = 2.54 cm = 0.0254 m

Therefore, d = 2.5 \times 0.0254 = 0.0635 m

                V =

                    =

                    = 38.73 m/s

Hence, we will calculate Reynold number as follows.

              =

                             = 2459355

As > 2000 then, it means that flow is turbulent.

As, f = 0.079

        = 0.001994

Putting all the values into equation (1) formula as follows.    

                                     =

                                      =

Thus, we can conclude that friction loss from the main to the discharge point is .

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