Pressure in Pipe/ data from hydrant flow tests 2

[199292]

It has been a while since I have had to interpret the results from a hydrant flow test using a pitot tube. For example I have the results of the static pressure to be 110 psi and the residual to be 75 psi. From this I assume I plug these numbers into the V=[2((110-75)*144)]/62.4 in order to get the velocity and from that number I should be able to get the flow through the steamer nozzle. Is the diameter of the steamer nozzle usually 5.25"? With this scenario I get a flow rate of 846 gallons per minute. Next question, should I be able to find the pressure in the pipe in the vicinity of that particular hydrant for any flow rate. For example could I calculate what the pressure is if I have 735 gallons per minute flowing through it using the reults of my flow test manipulating the equation from above. I would like to then plug this number, the pressure number, into Bernoulli's eqaution to find if the pipe I am designing would meet certain flow and pressure requirements down stream. Some guidance would be appreciated.

 

[hydrae]

199292

You need to account for the venina contracta (sp) using the factor according to the entrance to the nozzle and a measurement of the actual diameter of the port both of which may be different for each brand of hydrant.
Use 0.9 for a smooth rounded entrance or if using a flow tube off the port.

To calculate the pressure drop in water distrubution systems use the HZ equation.

(Q1/Q2)^.54= (Ps-P1)/(Ps-P2)

Ps = static pressure
P1 = residual pressure while flowing Q1
P2 = residual pressure while flowing Q2

You have 3 of the 4

Hydrae

 

[LHA]

Hydrae is correct about actual nozzle diameter (and everything else in the method described).

Here in the USA, the most common standard nozzle diameter is 2.5", sometimes 3". I don't recall ever encountering a 5.25" nozzle on a hydrant. I think you mis-measured the diameter, and that will throw off v (and therefore Q) substantially.

 

[hydrae]

lha

It is common in some cities to have 3 port hydrants 2-2.5 ports and one 5" port, the 5" port is called the steamer port and will allow up to 2500 gpm out of a single hydrant providing the system can support that flow.

199292

Rereading the question again 199292, are you using a pitot tube? from you description I cannot tell. The static and residual pressures measured off the main (at a house or nearby hydrant, prefer downstream) and then the pitot tube pressure to get velocity through Bernoulli's equation at zero pressure, and adjust as shown above...

For pipe length and sizing using orignal HZ equation (the above equation is derived from the below equation setting lengths, roughness, and diameters remain the same)

Hl = 4.727* L * Q^1.852 / C^ 1.852 / d^4.871

HL = headloss in feet
Q = flow in cfs
L = pipe length in feet
d = pipe diameter in feet
C = Roughness coefficient(Hazen-Williams C-actor)

C = 140 for smooth (cement lined DI, or PVC)
C = 100 for unlined cast or steel
Other numbers as determined by testing


Hydrae

 

[199292]

Hydrae,

I am using a pitot tube and I have used the equation Q=29.83*c*d^2*(p^.5). Then you mentioned the manipulated HZ equation in your first response and that was the equation I needed to proceed. Thank you so much for your help.

199292