Determining Service Line Pressure From Hydrant Flow Test
Determining Service Line Pressure From Hydrant Flow Test
(OP)
I just recently graduated and I am having to determine the water pressure of a 2" service line at the site of a new industrial facility. The facility will require at least 35 psi at the meter and is located 2,715 ft from the nearest fire hydrant. The site is 78ft higher in elevation than the hydrant as well. The only information I have is hydrant flow data. The hydrant (hydrant #1 on attachment) is tied into a 6" water main and just past the hydrant drops into the 2" service line and runs up the hill. So far all my attempts to use the hydrant flow data and find the end line pressure have resulted in huge head losses (over 7000ft using Hazen-Williams). Can a hydrant flow test be used to determine the pressure at the end of this line? Any help or advice would be greatly appreciated. From what I have calculated, this 2" service line running this far uphill is not possible; however, the line already exists and has been utilized in the very recent past by a facility across the street. Thanks.





RE: Determining Service Line Pressure From Hydrant Flow Test
Note that the minimum operating pressure in the water system should be approximately 40 psi.
A 2-Inch water line will be able to provide pressure when flowing at 3-5 ft/sec. At 3 ft/sec (30 gal/min, you will have 81 ft of headloss. At 2 ft/sec (30 gal/min, you will have 43 ft of headloss.
The question is, what water flow is desired?
If you need a significant amount of water, it probably will not work.
RE: Determining Service Line Pressure From Hydrant Flow Test
RE: Determining Service Line Pressure From Hydrant Flow Test
RE: Determining Service Line Pressure From Hydrant Flow Test
RE: Determining Service Line Pressure From Hydrant Flow Test
RE: Determining Service Line Pressure From Hydrant Flow Test
You need to model the existing system losses as well as losses in the new service. The hydrant test gave data to model the existing; 2 points on that curve are 75 psi at 0 gpm and 45 psi at 450 gpm. At the end of the 2" service you want to find what flow is available at 35 psi. Elevation loss of 78 feet is 34 psi, so at 0 flow the pressure is 41 psi at the "meter". There is 6 psi available (41-35), to be lost in existing system and new pipe. What pipe flow causes approx 5 psi pressure drop?
RE: Determining Service Line Pressure From Hydrant Flow Test
RE: Determining Service Line Pressure From Hydrant Flow Test
RE: Determining Service Line Pressure From Hydrant Flow Test
The hydrant test does not relate directly to service pressure. The hydrant test is a scenario where you would have one significant user of 450 gpm.
If you have the flow of 18 gpm as given, that would be 35 feet of headloss in the 2-Inch pipe. Adding in the elevation difference of 78 feet, which would give you a total of 49 psi pressure difference from hydrant No. 1. The resulting pressure is then 26 psi.
As cvg noted, this is probably unacceptable since the minimum service pressure should be approximately 40 psi.
RE: Determining Service Line Pressure From Hydrant Flow Test