Low Pressure Sewer question

[bws222]

Hi,
I was hoping someone with experience in low pressure sewer design could help me. We are working on a small lps system to serve roughly 30 houses. The best reference I have found is the EPA's manual on alternative sewer systems. My question is about calculating the design flow for pipe sizing.

The EPA mentions two methods for this; probability and rational. The probability method is based on probable number of pumps running simultaneously and pumping rate (only recommended for progressive cavity pumps). The other method is the rational method which is based on flow rate/dwelling unit.

We are proposing a centrifugal pump. I have worked on a smaller lps system in the past and we had access to the FE Myers Collection systems manual and they used the probability method for centrifugal pumps as well. Just wondering what method others use for centrifugal pumps. Also I was wondering are zones required when using the rational method. My understanding is that zones are set up when the probable number of pumps operating simultaneously increases by one.

Also any other reference for low pressure sewer would be great.

Thanks for any help

 

[CarlB]

http://www.eone.com/

is used for a lot of LP sewer systems.

see also
thread161-225849
thread161-194697

 

[bimr]

The semi-positive displacement grinder pump in the LPS pump station has a nearly vertical H-Q curve. This is the best type of pump for successful parallel operation of many pumps into a system of common low pressure mains. Since each pump will be located at a different point along common low pressure mains and at various elevations, each pump should operate in an efficient and predictable manner, whether one pump or numerous pumps are operating at a given moment; the pumps in such a system do not have a single fixed "operating point," but must operate consistently over a wide range of heads that are continually, and often rapidly, changing.

The E/One grinder pump has the capability of operating above the LPS system design criteria of 80 psig. Based on the maximum daily number of pumps operating simultaneously versus the number of pumps connected to the system at the design pressure of 80 psig, the capability to operate significantly above the system's design pressure is mandatory in order for the system to operate properly during the approximately bimonthly peaks when the "absolute maximum" numbers of pumps are operating. This feature also ensures that pumping will continue under those conditions when higher–than–normal pressure occurs in the pipeline.

Contact Orenco or E/one for design information.