Pressure reported for hydrant test vs main pressure 2

[khu]

I'm trying to determine the pressure of a 10" main from hydrant test results. For some reason, I've always assumed those pressures were actual system pressures, but the water board is telling me the pressure in this line is actually ~170psi. Is there a way to convert these pressures to main pressure? Is it the same??

Test results:

Static Pressure = 70 psi
Residual Pressure = 50 psi
Outlet Size = 5 inches
Pitot Pressure = 18 psi
Flow = 2,850 gpm
Calculated Flow at 20 psi residual = 4,600 gpm

 

[cvg]

municipal water distribution systems rarely if ever have pressures as high as 170 psi. I would question that.

static pressure at the hydrant will be close to the static pressure in the main. but use caution as watermain pressure varies a lot depending on day of week, time of day, pumps on/off and tanks full or not, etc.

 

[LittleInch]

I too would have assumed the static pressure was the pressure in the mains. Unless there is some sort of pressure regulation going on the 170 figure seems incorrect.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[coloeng]

[municipal water distribution systems rarely if ever have pressures as high as 170 psi. I would question that.]

That may be true in relatively flat areas, but in mountainous areas there are often times where the pressure is in those ranges. In our system our highest pressure on a distribution main is 190 psi. I worked for a previous system that had a pressure of 240 in a transmission main. We are in the Rocky Mountains.

 

[cvg]

different strokes for different folks

transmission mains are a different animal
and the systems I have worked on, even in the mountains we kept the maximum pressure to 120 for both transmission and distribution

 

[mk3223]

Some possible reasons are for the discrepancy of the pressure of the water main and hydrant, such as there is an elevation difference between two locations, or the pressure of 170psi is the line design pressure but 70psi is the actual line pressure while performing the hydrant test.

 

[amlinerrichard]

If the main pressure is 170 psi, the fixtures in building hooked up to it would be blowing fixtures all over. The main is probably 10 feet deep so the pressure at the hydrant may be 5 psi less due to the lift to the hydrant.

 

[fel3]

amlinerrichard...

If the main line pressure is 170 psig, then building plumbing would be protected by pressure regulators.

Back in the 1980s, my company consulted for a water district in southern California that had main line pressures ranging from about 30 psig to as high as nearly 300 psig in a few places. Buildings with service pressures below 43 psig (100 ft of head) had an "elevation agreement" whereby the owner accepted lower-than-normal pressures. Buildings with service pressures above 80 psig had pressure regulators. For service pressures between 80 psig and 150 psig, the regulator was between the meter and the building and was the responsibility of the owner. For service pressures between 150 psig and 300 psig, the regulator was between the main and the meter (to protect the meter) and was the responsibility of the water district. BTW, the highest pressure in the entire water system was 590 psig on the discharge side of a pumping station that pumps WAY up a hill to a water tank. But, there are no service connections along this line.

I lived in Ventura at the time. The main line pressure outside my house was 135 psig. I learned this when my regulator failed at 4:45 on the Saturday afternoon before Memorial Day. The ONE plumbing supply store in town that was open on Saturday was closing in 15 minutes, but the owner agreed to stay open until I could pick up a regulator. (I had first called a couple home improvement stores and hardware stores closer to home, but they didn't have pressure regulators.)

Fred

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[cvg]

Fred - what water district was that?

I worked as district engineer for literally a dozen different water districts in the Inland Empire and none had such high pressures. Chino Hills, Rialto, Colton, parts of Fontana, East San Bernardino, Baldy Mesa, Mission Springs, Running Springs, to name a few. most districts chose to keep pressures lower partly because the amount of leakage is in proportion to the pressure and also because we were the engineer setting the pressure zones. Especially with some of the older systems, it just didnt make sense to crank up the pressure so high and replacement of all the lines with higher pressure pipe was expensive.

 

[fel3]

cvg...

Las Virgens Municipal Water District in western Los Angeles County. It covers the cities of Hidden Hills, Agoura Hills, and Westlake Village (all between the San Fernando Valley and Thousand Oaks) and a lot of unincorporated areas, including a couple areas NW of Chatsworth that are not contiguous with the bulk of the district.

The pumping station with the high pressure was designed before I got to Boyle Engineering's Ventura office in 1981. The engineer who designed it gave me the background when I was modeling the subsystem on top of the mountain on the other side of the tank his pumping station pumped to. In my five years there, I did a lot of water system modeling for the district related to proposed developments. Some of these developments stretched up and down steep hillsides, so we ended up with lots of abnormally high and low pressures and sometimes it wasn't economical to carve out a new subsystem via pumping station and tank or via master pressure regulator.

Fred

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[cvg]

did the same thing all throughout the inland empire 85 - 94