EPANET set up / 25% drop in pressure during flowtest

[ieranger]

I have an existing 12" waterline looped off of a 20" waterline and I am trying to set up an EPANET Model. We are trying to determine available fireflow / pressure in a new waterline that will loop from the 12" to the 20". A hydrant was recently flowed near the proposed tie-in on the existing 12" with the static and residual pressure measured at a nearby hydrant. To set up the EPANET model I have all of the existing 12" information input into the model and tied into the 20". I have then simply placed a reservoir at the end of the 20" at the elevation that provides the measured static pressure at the hydrant and then placed the observed flow as a demand at the flow hydrant and then extended 20" line until the pressure at the measured hydrant was equal to the observed residual pressure from the flow test. Is this correct? I have seen reference to placing a reservoir at the flow hydrant with a pump to match the observed flows and pressures. Is either way more correct? The former method is more intuitive for me.

And during the flow test, there was only a 4 psi drop observed; however, code requires 25% or equal fire fighting flow. We will be flowing more hydrants to match the code requirements and hopefully better calibrate the model, but what is the reason to require an observed drop of 25%? Thanks for any inputs.

 

[RWF7437]

Sounds confusing.

Try modeling this with TWO reservoirs; one at each end of the 20" line. Then assign a flow at the hydrant(s) of interest equal to the required fire flow. Then note the lowest residual pressure. Is it 20 psig or more ?

"We will be flowing more hydrants to match the code requirements and hopefully better calibrate the model, but what is the reason to require an observed drop of 25%?"

I've never heard of such a requirement. The usual requirement is that you be able to deliver the required flow at a minimum pressure of 20 psig. I don't understand what a drop of 25% means. 25% of what ? Are you sure you've read the code correctly ? Can you post it ver batim ?

good luck

 

[ieranger]

the 25% drop in pressure from static to residual during flow testing is per NFPA 291. We are required to perform the flow tests per this code. The NFPA 291 code actually has nothing to do with the actual fire flow requirements. maybe kind of non-sequiter to add that to the end of the first question. thanks.

 

[RWF7437]

"NFPA 291: Recommended Practice for Fire Flow Testing and Marking of Hydrants"


Indeed, this doesn't seem to have much to do with our original question. I don't have a copy of this standard so can't say for sure.

Meanwhile, try my earlier suggestions for modeling this.

good luck