Information needed to properly select a pump:
Sizing a sewage pump:
- What is being pumped?
- How high do you have to pump vertically?
- How far do you have to pump horizontally?
- Type and size of pipe
There are actually three ways to size a sewage pump. Each method will provide an estimate of peak flow conditions.
- Fixture unit calculation
This method uses the "Hunter Curves" for approximating water usage by a typical plumbing fixture. This is an acceptable way of estimating the pump flow requirement for residential and small commercial applications.
- Larger capacity system chart
This is a derivation of the fixture unit method. It takes into consideration that in a high density environment, a ratio of plumbing fixture use can be applied to approximate peak flows. This method can be utilized for structures such as motels, apartment complexes, trailer parks, large office buildings, etc.
- Population method
Method of calculating demand used by civil engineers when designing municipal sewage systems. A gallon-per-day usage pattern is established for each type of building structure. Then, a peak factor is applied, which is spread over a 24-hour period. This method is used for homes and other residences where sewage flows into a municipal sewage system. This method can only be used in those applications where a large basin is used.
Regardless of what your peak flow requirement is for a given application, the pump must always be able to provide a minimum velocity of 2 feet per second through the line. Line sizes, with their accompanied minimum flow rates, are as follows:
1.25" - 9 GPM
Other factors concerning pump selection:
1.5" - 13 GPM
2" - 21 GPM
3" - 46 GPM
4" - 78 GPM
6" - 180 GPM
8" - 320 GPM
10" - 500 GPM
- Total dynamic head (TDH) in feet is the total resistance in the piping network which you are pumping against. Do not select a pump if the TDH is less than the minimum point shown on its curve.
- The pump selected must be capable of pumping to the highest vertical point in the system.
- Do not under-size the basin. If possible, always select a pump and basin assembly which will allow for at least a 30-second pump cycle and no more than 6 starts per hour.
- Air can interfere with the pump's ability to work. Always drill a vent hole in the discharge line between the pump and check valve. In long horizontal runs of pipe, air relief valves may be required.