CALCULATE THE HEAD, GPM AND HP OF THE PUMP

 

FIREFIGHTING SYSTEM

It is very necessary to understand the head loss, GPM, and power consumption of the pump in the firefighting system before installing it in the project. We must be aware of the elevation, number of hydrants, floor area which the hydrant should cover, and also the access to the municipal line for the case of emergency.


STEPS: 

TOTAL HEAD= HEAD LOSS DUE TO PIPES + HEAD LOSS DUE TO FITTINGS+ RESIDUAL                                  PRESSURE REQUIRED AT THE FARTHEST POINT (6.9 Bar/100 PSI) + HEAD                                LOSS DUE TO ELEVATION (HERE FIRST TWO NEEDS WORK, OTHER CAN                               BE EASILY CALCULATED)

        1.    RESIDUAL  PRESSURE REQUIRED AT THE FARTHEST POINT=  (6.9 Bar/100 PSI)

         2.   PSI  FOR HEIGHT= ELEVATION (in m)/ 1.428    (1.428 PSI FOR 1 m Height of Water)

        3.    TOTAL LENGTH OF THE PIPE= SUM OF PIPE TO THE FARTHEST POINT

        4.    TOTAL EQ. LENGTH OF THE PIPE= SUM OF EQUIVALENT LENGTH OF ALL                               FITTINGS

                 PSI/FEET OF EQUIVALENT LENGTH= 4.52 * (Q)^1.85/(C^1.85 * d^4.87 )

                                                                    Q= FLOW IN GPM THROUGH PIPE

                                                                    C= HAZEN'S WILLIAM C VALUE= 120

                                                                    d= DIAMETER IN mm =(150mm, 120 mm according to                                                                             pipe size)

                     For 750 GPM FLOWING THROUGH 150 mm, C= 120 (Look @table below) Q=750, d=                       6 inch

                     PSI LOSS PER FEET= 4.52 * (750)^1.85/(120^1.85 * 6^4.87 )  = ALMOST .0217                                 PSI/feet

                                    Head loss due to pipes= (pipe length in ft)x .0217

                                    Head loss due to fittings= (pipe equivalent length)x .0217   = (almost 20% of                                            head loss due to st. pipes normally)







EXAMPLE


Last two hydrant of Last Riser= 500 GPM
REMAINING RISERS= 250 GPM EACH

From above we found out that: 
Head= almost 100m


Now for Calculating HP of Pump = 
3,960×0.65
750×100​
= 29 HP




find attached excel calculator



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