Intermittant distribution system low pressure remediation

[smaug6]

I am analyzing a water system that has intermittent low system pressure. The situation is that this system lies on a lake and experiences periods of very high demand. I am sure the distribution system; which consists of a standpipe elev. 812 ft 37 ft high. and approximately 2.6 miles of unlooped 8" pvc water main with a 50 psi PRV at 650 ft in elevation followed by approximately 2 mi of 6" PVC main to eventual service elevation of 683 ft is inadequate for the job and should be upgraded. The service population varies such that the hydraulic grade line lowers and high areas within my area of interest lose pressure on occasion. My concern is this; if I spec. a VSD pump system to mitigate the intermediate low pressures could cavitation become an issue during times of high demand or I would think it probable I could collapse the line feeding the pump station (elev. 605 ft.). Any feedback would be appreciated.

 

[BigInch]

Let me confirm,

Supply point is at elev 812 ft
2.5 miles of 8" to elev 650 : Pressure reduction to 50 psi
2.0 miles of 6" to elev 683

Now...

Question 1: Why the Pressure reduction?

If you CAN remove the pressure reduction valve at elev 650 ft, I think it looks like you can get about 1000 gpm from that supply elev of 812 ft to elev 683 ft for distribution with about 50 psi left to distribute. (I didn't do a real flow analysis, but it looks approximately correct.) So... I don't see where you need a pump at all, never mind a pump with a VFD too.

Question 2: What are the maximum allowed pressures in the 8" and in the 6" pipelines?

Question 3: What maximum flow rate output do you need at the distribution point at elev 683 ft.?

Question 4: Why do you want a VFD?

We wait for your answers (especially to question #1, but don't forget about the other 3 questions either.)

http://virtualpipeline.spaces.msn.com

 

[bimr]

You have not provided enough information for someone to make an informed comment. What is your population for example?

 

[BigInch]

Isn't it the flowrate that is needed to determine the answer to the questions asked?

If you ask about the population, then you have to ask what's the maximum demand in gallons/person or something. Why not just ask what flowrate he wants?

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