A Primer On Septic System Pumps
When your septic system incorporates a pump, understanding how that pump functions, what it’s doing, and what to expect when it fails is important. Depending on the type of pump, and what it’s purpose is, the necessary maintenance, lifespan, and cost of replacement can vary greatly. This primer will discuss the most common uses for pumps in onsite wastewater treatment systems, the different types of wastewater pumps, and how they are controlled.
Why pumps are used in septic systems:
The most common reason a septic system will have a pump, is to deliver sewage to a tank or soil treatment area that is higher than where the wastewater exits the home or the septic tank. When pumping from the home to the septic tank, the pump may be located in an interior pump vault in the basement of the home, or may be housed in a pump chamber on the exterior of the home. When pumping from the septic tank to the soil treatment area, the pump will be located either in the last chamber of the septic tank, or a separate pump chamber after the septic tank.
Another reason an onsite wastewater treatment system may incorporate a pump is to pressure dose the soil treatment area. Traditional septic systems rely on gravity to deliver effluent to the soil treatment area, but pressure dosing can have a variety of benefits including:
Even distribution of effluent throughout the lateral lines in the soil treatment area
Greater control over the volume and timing of effluent delivery to the soil treatment area
Ability to provide periods of “rest” for the soils in the treatment area between doses of effluent
By utilizing pressure dosing, designers can plan for systems in areas with more challenging soil types, increase the lifespan of soil treatment areas, and in some cases reduce the overall size of the system.
While it’s beyond the scope of this write-up, it should be noted that there are many other, but less common, reasons a system may utilize pumps. Some examples include recirculation pumps for advanced treatment units, alternately dosing different soil treatment areas, and metering the flow of wastewater to other components in the system.
What kinds of pumps are used in septic systems:
Not all pumps are the same. Using the correct size pump, and the correct type of pump is crucial to ensuring that the system functions as intended, and that the pump lasts as long as possible. When pumping from the house to the septic tank, there are two types of pumps that are commonly used, Grinder and Sewage pumps. Grinder pumps work, as the name suggests, by grinding the solids in raw sewage into a fine slurry and then pumping that slurry to the septic tank. Sewage pumps, on the other hand, work by passing the solids along rather than grinding them. There are pros and cons to both.
Grinder pumps tend to be more robust, and since they grind up the sewage, there is less chance that they will clog; however care should still be taken with regards to what is sent down the drains and toilets. On the other hand grinder pumps tend to be more expensive than sewer pumps, and the fine slurry they create has a harder time separating into solids and liquids in the septic tank. Due to the lack of solids settling, filters in the tank will clog faster, the soil treatment area may have a shorter effective life span since solids are more likely to make their way to the lateral lines, and the septic tank may need to be pumped out more frequently.
Sewage pumps tend to be better for the septic system, as they do not grind up the solids coming from the home. Because of this the waste stream delivered to the septic tank is able to settle more completely into solids and liquids, and the effluent leaving the tank will be clearer. Sewage pumps tend to be cheaper than grinder pumps, so replacing them when they eventually wear out is more cost effective. The reason sewage pumps are not more desirable in all cases is that since they only pass along solids, they are more prone to getting clogged. Most sewage pumps that will be found in residential applications can only pass 2” spherical solids, and much more care must be taken in the home in regards to what is being sent down the drains and flushed down the toilet.
When a pump is needed to transport liquid wastewater (effluent) to the soil treatment area, effluent pumps are used. In these situations the solids have already settled out of the wastewater, and often times that wastewater has passed through a filter, so the pump doesn’t have to handle any solid waste. As the name suggests these pumps are not designed to grind or pass solids, and if solids do make there way into these pumps the risk of them clogging or breaking is much higher. It is important to get the septic tank pumped at regular intervals, and to clean the filters to ensure that the effluent pump lasts as long as possible.
Pumps are sized based on how fast they need to pump (gallons per minute), how far, high and through what size pipes they need to pump (total dynamic head), and how much pressure they need to provide when used in pressure dosing applications. The sizing of a pump depends on much more than just how many horsepower the motor is.
If you are having trouble with a pump, or you need a pump replaced in your septic system, the professional technicians at Ruby Septic can help. Feel free to contact us with any questions you may have.