Sewage Wastewater Lift Pump Design Considerations

Properly designed Wastewater Lift pump systems require some basic attention that most plumbers just fail to address. When designing your Sewage lift unit, we recommend that you consult a registered engineer to ensure that your system will work reliably for years.

We reviewed internet posts, which present guidance for homeowners and plumbers to use when choosing a Sewage wastewater lift system. Most of the internet “advice” we reviewed fails to consider some critical pump design elements. This article attempts to highlight a few minimal design considerations which we feel should be addressed.

Firstly, what type of wastewater requires pumping? For example, various sewage pumps can pass different size solids from small quarter inch pieces to up to 2.5 inches in diameter. For larger size solids, grinder pumps are used, much like a garbage disposal, to chop up the solids into smaller particles that can be pumped. Therefore, if we are pumping screened or filtered wastewater, a liquid pump is adequate. The liquid pumps are generally multi-staged pumps and can deliver a high head (pump outlet pressure). If solids are screened in larger pieces, then specially designed lift pumps can be used which can pass the larger solids.

All pumps require a minimum net positive pump suction head (NPSH) to minimize cavitation. If the pump cavitates excessively, then the impeller will wear out, possibly in a year or so. A properly design system ensures that the correct pump is chosen which will match the system, minimizing cavitation and extending pump life.

The figure below is pump curves for the basic NORWECO wastewater lift units and a “typical pump placement.” The pump curves are the curves bending downwards. Each pump has a different application and you select the appropriate pump based on the desired lift height and the resulting system curve. The system curve, in this example, curves upward. Where the pump and system curves meet yields the flow rate and pump lift height when the pump is running. Generally, you meet NPSH requirements if the pump curves intersect without extrapolation.

The system curve should ALWAYS be calculated as noted in the bottom of figure one. The calculation ensures that the pumps operate in an acceptable range. As a homeowner or contractor, you should ALWAYS ask to see the pump and system curves for your application. Please do not trust an installation that does not perform the calculation, force your plumber or engineer to provide one.

One additional consideration is the pump chamber height and/or lift. I notice many “sewage pump units” offered on the internet. The pump units are short and fat sumps. We estimate that these systems are very inadequate. When the pump sump height is too low, the pump will tend to short cycle. The “short cycling” can cause excessive pump wear. Also, the on/off and alarm settings tend to be unreliable due to the short travel distance (the pump sump height is much too small) in liquid height. In the NORWECO pump units, you adjust the pump sump heights are by adding segments to the sump. This gives the design engineer flexibility in pump designs which ensure maximum pump cycle times and proper NPSH.

Please consider our line of NORWECO lift stations. Our pricing is very competitive and we do maintain staffs of registered engineers, which can provide complementary lift pump calculations with every purchase. We feel that the NORWECO pump units are the best pump units on the market today.

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