Water lost in a fire hydrant

[lordtemple]

I'm doing calculations for how much water was lost when flushing a hydrant. It is a 2.5 in. outlet and the pressure is on the system is 40 psi. It was flushing for 1.5 hours.

Q=AV

V=[(2 dP gc)/density]^0.5

density = 62.4 lb/ft^3
dP=40 psi
gc=32.2 lbm ft / lbf s^2

V=77ft/s

Q=AV=(0.0340)(77)=2.6 ft^3/s=19gal/sec

The hydrant was flushing for 1.5hrs = 90mins = 5400secs so...

The water lost was 19*5400=105,892.77 gals??? is that right?? can you check my general theory of my problem?? it seems to me a little bit high to loose 100,000 gals in 1.5 hours for flushing a hydrant... don't you think?

 

[CRG]

I do not see any concern for viscosity and friction. The calculation cannot be accurate.

 

[hydrae]

Lordtemple

You need a more accurate way of measuring the flow:
pitot meters are available from waterworks supply sources, with the gauge comes the equations that will give flow based upon pressure read off the gauge, the diameter of the port and the edge factor of the nozzle.

Without that device use the following equation
I figure equation accuracy within 10 to 20%
Q = 2.83 * d^2 * L * h^.5 * C
Q = flow in gpm
d = diameter of port (2.5) inches
L = distance the stream of water hits the ground from nozzle edge (inches) typ 10 to 200 measure it you may get wet...
h = height from ground to center of nozzle (inches) (8 to 36) measure it
C = nozzle factor .8, .9 or 1: Feel the inside of the nozzle adjust with the following factors
inset sharp edge = .8
sharp edge = .9
smooth or rounded edge = 1


Flow can be as high a 1000 gpm from a single 2.5 port, at 90 minutes 90,000 gallons very possible but only if system losses are small.
Typical system static pressures at the hydrant 40 psi I would expect a flow in the 400 to 650 range depending upon the diameters and lengths of the supply piping network.

Hydrae