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How to size a sewage ejector system?

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708 views asked Aug 29, 2014 by Mepanet

1 Answer

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  1. Count all the sanitary fixtures (users) fixture units (FU) in system which are covering by sewage ejector and add them up to determine the total FUs in system.
  2. Convert the total FUs to gpm by using below formula:

                          gpm = total FUs/ 2
                          Each gpm is equal to 2 FUs


  1. The Static Head : The actual vertical distance of “lift” in feet from the minimum water level in the basin to the highest point in the discharge piping.
  2. The Friction Head: The friction losses caused by pumping the fluids and solids through the various piping and fittings. 

Selecting the Pump:

Using the Capacity (GPM), Total Dynamic Head, and solids handling requirements, refer to the pump performance curves to determine the best pump for the application. Select the smallest pump that meets the Capacity and Head requirements and can pass the required solid size. 

Basin size

To determine the proper basin size, refer to the required GPM of the system, convert this to the volume the pump must be able to pump out of the basin during each cycle using formula:  

                     GPM x Run Time (min.) = Volume (gals)

The run time must be at least 2 minutes to ensure against short cycling (which would greatly reduce the service life of the pump). 

Pump Quantity:

Most commercial applications requires duplex pump systems to guaranty stand –by safety factor that many municipalities require (public health concern). In most residential installations, a simplex system is adequate. Exact requirement shall be verified with the local plumbing and municipal codes. 

Size of solids:

  1. Building with water closet will pass 2 inch solids and will require a Sewage Pump.
  2. If building does not have a water closet it will only need to pass 0.25 inch or smaller solids, and will require Effluent pump.  
answered Aug 30, 2014 by Mepanet

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