Pipe flow through a small network 1

[eskerley]

I am having trouble figuring out how to begin this analysis. The project I am working on is proposing to add 3 yard hydrants to an existing waterline. I know the pressure at the waterline we are tying into, pipe diameters, and yard hydrant diameters. My understanding is that this is a parallel pipe network problem with 4 pipes all existing to atmosphere, so headloss in each branch is equal.

Watermain = 4" @ 65 psi
Hydrant 1 through 3 = 1.5" yard hydrants
Hydrant 4 = 2.5" hydrant
Hydrant exists are +3' higher than the watermain connection
Service line will be 145 ft of 3" pipe.
yard hydrants will be ~1' from service line

I am getting stuck at the fact that I only have pressure at the beginning of the system, I don't know velocity because I don't have the headloss. I could do some type of iteration (assume a headloss, get a velocity, circle back to check headloss), but not sure if that is the best way to do it.
How do I go about calculating the pressure/flow rate at each hydrant when they are all open (worst case scenario)?

Side note, I attempted to use EPANET to model the system, but the results I am getting don't seem to be correct. See attached screen shot for schematic.

Any help would be greatly appreciated.

 

[bimr]

You need to explain what you are trying to do. Are these hydrants for fire service or yard hydrants?

Fire hydrants are flow-tested at a residual water main pressure of 20 psi; therefore, you should understand the typical flow rates of fire hydrants. The flow rate of a hydrant is typically identified by determining the available flow rate when the residual pressure drops to 20 psi. The hydrant manufacturer should be able to supply the water flow curve for various pressures.

NFPA handbooks tell you to use water main velocities between 10-20 ft/s. With a 15 ft/sec velocity, the 3-Inch pipe will flow about 330 gpm with a headloss of about 19 psi.

This preliminary calculation indicates that if all hydrants are open, the flow capacity from the hydrants will be limited by the capacity of the 3-Inch water main.

 

[eskerley]

Thanks for the response.

These are just yard hydrants, no fire flow is required. I am wanting to make sure there will be adequate flow to each yard hydrant in the event that all yard hydrants are in use, however unlikely a situation that may be.

 

[1503-44]

Assume atmospheric pressure for the discharge pressure at each of your hydrants.

A black swan to a turkey is a white swan to the butcher ... and to Boeing.

 

[coloeng]

For a system like this, accurate minor losses are extremely important. If you haven't determined what the minor losses are for each bend, tee, transition from pipe to hydrant, etc. you won't get an accurate outcome in your model.