Hydrant Testing - Opened two ports

[hydrant_testing_101]

This may be a stupid question, but we recently did some hydrant testing where we knew the previous test results showed an issue with getting adequate pressure drop from the static to residual pressure. Therefore, we opened the 4" port to test the flow of hydrants where we were able to. However, where we were not able to open the 4", we attached a special adapter to the 4" which ran a 25' 4" hose to a 4"x3"x3" tee and flowed into the street. We also opened the 2.5" nozzle and measured the pitot pressure out of that and recorded that as our pitot pressure.

Is it possible to calculate the hydrant flow with these parameters?
I realize it is not ideal and we should have stuck with opening the other 2.5" nozzle as opposed to the 4", but I don't want to go back out and re-test these if we don't have to...

Any information anyone can provide would be greatly appreciated.
Thanks

 

[mk3223]

I think you may add the DP of the 25' long hose to the pressure see at end of hose which is to be the actual pressure at hydrant.

 

[hydrae]

Did you pitot both locations
The small port at the hydrant and one of the 3" ports on the tee? they would have been different.

If not, yes it could be calculated but it would be highly iterative and not something I would trust to submit to a fire flow calculation

Hydrae

 

[hydrant_testing_101]

We did pitot both ports, but only at 2 out of the 7 locations that were tested that way...

I understand there would need to be some assumptions made in order to calculate the fire flow, I just need to determine what assumptions those are and report those.

Thank you!

 

[hydrant_testing_101]

Any idea what assumptions would need to be made? I know the pitot reading out of the 2.5" that we did measure would be slightly less than what a typical reading would be without opening the 4". But is there an assumption we can make for the 4" flow nozzle being open and add the two together to get our hydrant flow?

I understand this is not ideal nor should it be considered for actual fire flow purposes, however the only alternative is re-testing and I am trying to avoid that.

Any recommendations would be appreciated.
Thanks!

 

[hydrae]

If you had very little pressure drop in the residual while opening the small port and just a little bit more drop when opening the large port through the hose and tee, how much water is needed?
Sounds like you are on a network where the available fire flows are enormous or very close to a source such as an elevated tank, in which case I would limit the fire flow to a velocity in the nearest main.

Another issue I have run into during fire flow tests, if the residual is taken at a nearby hose spigot there may be a backflow device preventing accurate reading of the residual pressure. The pressure vacuum breakers are incorporated into nearly all the spigots installed recently.

Hydrae