LOW PRESSURE FORCEMAIN 1

[water017]

I am doing a low pressure force main with multiple grinder pumps feeding into the forcemain at different points. I have done many forcemains from one lift station source, but never a multiple pumps on the same line at different entry points.

Just wondering if there are any things I need to consider that you wouldn't look at on a tradional lift station forcemain.

any thoughts would be appriciated

 

[LHA]

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[kchayfie]

As I see it, you are essentially talking about a pumping station with multiple pumps, albeit spread out over a much wider area, with pumps in individual wells rather than the same well. You need to give it the same considerations as a station with a duty/assist pump set but take care in selecting which is the "worst case" pump on the system. If the different pumps are located at different levels, a deeper pump connecting further downstream at a lower level might need more pressure than a pump that connects in first, but from a higher level depending on the relative flowrates and the dynamic losses in the system.

 

[redbridge]

You will just need to figure out how many grinder pumps will be running at the same time. The grinder pump companies or the regulatory agency can help you come up with that number. Then design and run a worst case simulation and you should be fine. The grinder pump manufactures will actually simulate the system for you. I always design a system and then compare to the manufactures.

 

[bimr]

You have to be concerned with the minimum flow to maintain solids in suspension in the force main. That would be 1 -1/2 to 2 ft/sec.

 

[CivEnvEng98]

As far as previous posts: Lburg has it right. I would check with any grinder rep to confirm the number of grinders you model as being on simultaneously. It is not the same as how you look at a force main system.

Also, I would be surprised if any permitting agency would allow less than 2.0 fps, but I would check before investing any time into it.

Just keep in mind that some utilities with low pressure systems use PVC, SDR 21 pipe. This means you can actually use pipe diameters ranging in 1/2-inch increments from 1.5-inches in diameter and up through 3.5'inches. 4 and above just use C-900.

One of the largest low pressure systems in the USA is in the City or Port St. Lucie, FL and they use Myers exclusively. Their specs should be useful if you want to see what they use for fittings as well.

 

[stanleyleecm]

Here is the link to EONE sewer design guide. You will find out all the information you need including detail calculations.

Hope this will help you out, btw design guide start on page 12.

http://eone.com/downloads/products/lps_design_manual.pdf