hydrant flow tests and their use in the hydraulic calcs 1

[pipesnpumps]

Taking a survey here..

I am curious what the NICET or FPE folks think is a completely correct design submittal, as it relates to a proper NFPA 291 hydrant flow test and the use of that flow test data in the NFPA 13 hydraulic calcs..

I know what I think, but what do you think?

For example, do you include a schematic showing the residual hydrant and the ug piping on your plans? What point do you consider as "the source"? etc.

Opinions seem to vary.

 

[MGXFP]

Personally, I calc back to the flowing hydrant shown on the site plan.

In the remote area hydraulic data info I include the pressure and flow at the base of riser/fire pump outlet and pressure and flow (+ hose stream) at the flowing hydrant.

 

[pipesnpumps]

Interesting NewtonFP.

Now let my pose another question for the sake of discussion. What if the residual hydrant reading the pressure is a long ways upstream from both the flowing hydrant and the new building run-in on a dead end UG main..?

Your calc assumes the entire residual pressure (at the residual hydrant) is available at the FLOWING hydrant. But in fact the flowing hydrant will have less pressure available since it is downstream, and there are pressue losses between the residual hydrant and the flowing hydrant..

So why would you not calculate losses back to the residual hydrant, since that is the supply pressure you are using for the design? This difference would almost never make the water supply become inadequate, but it could.. Elevations would also affect it.

I don't understand why some people calculate down to the gnats ass for branch line fittings etc. but the water supply is a simple "gpm @ residual", without an elevation, location, and with some guess at the equiv length of the lead-in.. Hydrant location is not shown on any plans. And they calc to the flowing hydrant.

 

[Oremus]

It would make more sense to calc back to the test hydrant (static/residual hydrant) than the flow hydrant. My elevation differences are accounted for in the calcs but not neccesarily shown on the site plan.

For light/ordinary hazard systems I usually don't show the hydrants and only calc back to where the fireline taps into the city main and call that out as the source node. Unless of course there are water supply issues or quite a distance from the tap to the test hydrant. The pressure losses are usually negligible for these type of systems when your connecting a 4" fire line into a 12" city main and requiring only 300-500gpm. Of course if there's water pressure issues and we're counting pennies then I'll take all that into consideration.

 

[MGXFP]

It's not cast in stone to calc back to the flowing hydrant, that's only what is usually done.

An engineer explained to me that if you get, say, 1050 GPM out of a flowing hydrant then when the calcs are performed pretend you're putting the 1050 GPM in. I.e. run it backwards like the rest of the calcs.

In the case of calculating back to the city main, losses in the water mains are usually quite low (not low enough to disregard IMHO).

Over the years I'm simply in the habit of showing which hydrants were flowed, where the static/residual pressures were taken and accounting for the underground, if that data isn't present then my plans are incomplete. Usually I'll get a topo map of the area via usgs and compare to the civil site plan and my elevations are above sea level so we don't have to muck about with AFF/ASL differences.

 

[spkreng]

I just calc to the 2" main drain valve, cause it's on the inspection report sheet......heard that one once, I'll calc to the intersection of the city main and call that source (unless unusual flow, elev etc) mains "usually" are going to be 8" and above, are looped and if hyd A is psi and B is flow and I'm coming off that line within a reasonable distance any loss would be negligible, if 1600 gpm at a loss of 3 psi in 150' would be a needed adjustment rather inclusion in the calc's.
I'll put the site plan showing all the hydrants, connections, etc as one of my plans with the flow data and getting that data from an owner / contractor is sometimes harder than getting a storage classification.

spkreng, CET

 

[SprinklerDesigner2]

Reference the following sketch

http://img809.imageshack.us/img809/8707/watersketch.jpg

If the static and residual was obtained @ hydrant "A" then the calculations should include the length of 8" city water main pipe all the way to Hydrant "A". With the Hydrant "A" being the test hydrant (it is, the flowing hydrant is not the test hydrant) the calculations would go back to this hydrant and it doesn't matter if the flowing hydrant was "B", "C" or "D".

If the static and residual pressures were obtained on Hydrant "B" and Hydrant "C" was the flowing hydrant the calculations would have to be carried all the way to Hydrant "B". Actually you would carry them to the 8x6 hydrant tee.

In this case the hydrant you should be testing (that's the hydrant where the static and residual pressures are obtained) is hydrant "C" and hydrant "D" should be the flowing hydrant. If this was the case then the calculations should be carried to the 8x6 tapping tee and I would would go further in saying you would not be incorrect to adjust the available residual pressure that was lost due to the friction loss between the 8x6 tapping tee and Hydrant "C".

I've never had to do this always leaving it as an additional safety factor but what if the distance between the 8x6 and hydrant "C" was 900 feet?

If the hydrant was flowing 1,100 gpm the head loss through 900' of 8" C900 DR18 WOULD BE 0.007 psi/linear foot or 6.6 psi over the entire 900' length.

If the flow test yielded 65 static, 44 residual (static and residual obtained from Hydrant "C") flowing 1,100 gpm where would I be wrong calculating to 65 static, 50.6 residual flowing 1,100 gpm at the 8x6 tap sleeve?

I am not wrong.

Of course this is assuming the terrain is flat.

I see people mess up with this stuff all the time and it aggravates me no end. They constantly miss adjusting for elevation and sometimes it makes a huge difference.

It is awfully hard to eyeball a fall of 10' over a 500' distance. Ten feet (4 psi) can happen and you never know it.

FYI I purchased DeLorme Topo USA version 8.0 a while back and it has been great. It's a topographic map of the entire USA and as far as I can tell it is accurate to within a couple feet. Most of you know I fly, I'm a pilot, and I checked it against aeronautical VFR charts published by the FAA and it is really close. On an VFR chart all towers higher than 100' (my scud running days were long ago) are published and what they do is give the height of the tower above sea level then the actual height of the tower above ground level like (343). DeLorme has always hit it within one or two feet and I've checked a lot of them.

Also airports are dead on. Airport elevations are given at the geographical center.

The point of all this is I don't think most people give full consideration and weight to what elevation does. You live and flat land, like I do, but you would be amazed what you might come up with especially with hydrants 500 or 1,000 feet away.

So, given the previous example if the finished floor is 100.0 what if that hydrant is determined to be at elevation 81? You just lost 19*.433=8.2 psi... at the 8x6 tee you would be correct in saying the static is 56.8 psi with a residual of 42.4 psi.

I cringe whenever I see designers assign the elevation to what they think the pipe is buried in the ground. The elevation is the centerline elevation of the hydrant butt from which you attached the gauge to obtain the static and residual flows.

Same goes if your static and residual hydrant was Hydrant "A" and flowed Hydrant "B". Calculations would be carried to Hydrant "A" and the elevation of the source would be the centerline of the hydrant outlet.

 

[pipesnpumps]

SD2, excellent post and summary. It aggravates me too, glad to know I am not alone.

On the elevation thing, I've seen some calcs where they include the underground pipe back to where the non-flowing hydrant taps off the main, and then code in a dummy vertical piece of pipe to account for the elevation of the hydrant butt. I don't know why, probably software related, but if I see that I at least know they considered elevation..

I've never seen anyone use friction losses to bump up the residual pressure, but I agree it is fair game to take credit for that, in your flowing from hydrant D scenario.. But good luck convincing a semi-retired fireman plans reviewer of that, heh heh.

 

[SprinklerDesigner2]

pipesnpumps,

I've never used it either, I've always left it for safety factor, but I know it is there.

The proper flow test is the single most important task of the entire project.

 

[FFP1]

Hydraulic calculations should be included to the static/residual hydrant or to the specific system component where the established static/residual data is available for any "other" source. Elevation and other pertinent data regarding the water supply should be provided to support the review process.