By Chris Edmondson
Pumps used in commercial sewage lift stations come in a variety of types (effluents, grinders, etc.) To determine which type is right for your application you must answer two questions:
- What size solids will have to be pumped?
- What is the size of the discharge pipe?
Simply stated, you can’t pump 2-inch solids through a 1-inch pipe. If these are the parameters of the application at hand, then a grinder pump is in order to chop the solids into smaller, more manageable pieces.
This is but one example of how the pump duty will impact the type of pump you choose. The various types pumps are listed below, along with the applications for which they are most suited:
Best Suited For….
Dirty water applications where solids are not typically present and are unlikely to ever exceed 3/8”.
Partially or completely treated wastewater applications with solids of 1” or less.
Commercial sewage applications where solids are 2 ½” or larger.
Applications involving waste that includes long, stringy, and/or fibrous solids. Examples include raw sewage lift stations, storm water applications, paper mill waste, etc.
Applications where solid size is likely to exceed the size of the discharge pipe. These pumps have a cutting system made of hardened stainless steel to shear solids so they can pass thru smaller pipe. Also useful in high pressure discharge systems typically associated with groups of homes, motels, schools, shopping centers, etc.
Whatever pump is selected, it should be able to maintain a velocity of 2 to 8 feet of flow per second in order to meet the International Plumbing Code (IPC) requirements (See Table 1). However, it is always important to check with local plumbing codes, those codes may exceed the IRC requirements.
Select Pipe Size and Pump Discharge
Note: Maintains velocity of 2 to 8 feet per second
Your pump model selection will be based on the following:
- Flow rate
- Solid size
- Pump style
- Discharge pipe size
All of these details, along with the specific pump selection and control requirements, should be indicated on the drawings. Control requirements will include the type of Level Controller required for the pump system, along with all following components that are inclusive within the control panel itself:
- Starts with Overload Protection
- T-O-A (Test-Off-Automatic)
- Alarm Systems
- Automatic Pump Rotation
The basic control requirements vary little from one lift station application to the next, however, the voltage as well as the type of NEMA enclosure required will often vary. Selection of the latter depends on the location of the panel itself – whether it is indoor, outdoor, etc. Table 2 shows the various types of NEMA Enclosures used for sewage applications.
General Purpose Indoor
Rainproof Sleet Resistant, Ice Resistant
Water Tight & Dust Tight – Indoor and Outdoor
NEMA 4 with Corrosion Resistant Enclosure
Hazardous Locations – Indoor – Air Break Equipment
For more information, check out JMP’s webinar on designing sump and sewage systems.