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Have a flow test in a semi-rural area that has static pressures of over 130 psi but a residual pressure of 60 psi at just 500 gpm.
A flow test from nearly a decade ago shows worse results - with a static of around 120 and a residual of 20 psi at just 600 gpm. My initial concern with the older flow test was a partially-closed valve or obstruction in the line. With the newer test the residual pressure seems more reasonable, but other than something being wrong with the system is there a reason that would justify a residual pressure less than half the static at only 500 gpm of flow? Perhaps a system fed with small pumps and no tower? What are your thoughts? Posted anonymously for discussion. Discuss This | Submit Your Question | Subscribe
5 Comments
Brett Cooper
10/14/2019 10:30:45 am
Do you have any information about the existing underground pipe? How far apart are your test hydrants? It sounds like the pipe is experiencing significant frictional losses due to an obstruction, partially closed valve, buildup in the aging underground pipe, or an undersized underground.
Jon Hatcher
10/14/2019 11:56:00 am
There are several factors that could cause a low residual pressure. Obstructions and/or closed or partially closed valves are possibilities. I suggest also investigating whether or not the hydrants are on a long dead-end run and possibly far from the source. Or perhaps the tested hydrants are served by older and small diameter mains. A map of the mains (with pipe sizes) in the area will shed some light in to what is going on.
pete
10/14/2019 12:08:36 pm
My first thought here was long narrow dead-end run... 6". Also some purveyors have isolating valves open on a delayed pressure feedback loop. In one Mississippi community I've worked in they have a 2nd feed normally closed until pressure drops for a minimum 3 minutes. The delay is to keep it from opening and closing repeatedly before the pressure normalizes downstream. You have to flow the hydrant 3-5 minutes minimum for the valve to open providing water from both sides.
lee mailler
10/15/2019 08:18:43 am
The static pressure is independent of pipe size or condition. We've seen many housing developments that are miles from the nearest water tower that lose half of the static pressure when flow tested. 60 psi residual pressure is still a good starting point, though. 9/29/2020 09:32:38 pm
Well worth a read. Got great insights and information from your blog. Thanks. Leave a Reply. |
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