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Im currently doing an assignment where i have to design a water reticulating system for a small suburb.

I have planned out all my distribution mains and my reticulation mains and services

I also have the water demand(Q) for the houses using the Australian Standards for plumbing and drainage.

So i know my Q value from Australian standards given by the formula:

Q=3.637*10^-5 H^0.555 D^2.667

where:

Q=Flow rate (L/s)

D=pipe diameter

H=head loss gradient in meters per 100m given by: (h*100)/(L*1.5) where h= Head loss in meters head, L= index length in meters and 1.5 is a factor allowing additional head loss through fittings

So for example (this is the calcs i did on one of the reticulation mains with a dead end serving 3 houses)

If i have

Q=1.03 L/s

L=50 M

h=1.1

1.03=3.637*10^-5 * 1.46^0.555 * D^2.667

D = 43.16 mm

now using this with V=Q/A i get V to be V=0.709 m/s

Am i doing this right??? because the velocity seems to be very slow(even though the maximum allowable is 3m/s anyway)

and am i going about it the right way? i thought start from the demands from the houses and work backwards to the distribution mains that way i can calculate all the pressures,velocities and flows needed at the entrances of the reticulation mains.

and if this is right, what formula do i use to work out the pressure needed to at the entrance of this pipe to supply this flow and velocity? ive been reading fluid mechanics books all week and i cant seem to crack it.

Thanks in advance