Dewatering Pump Selection
This information is to assist you in determining the correct pump to use in various situations. There are several types of self-priming portable pumps. A self priming pump will clear its passages of air if it becomes air bound (meaning it can no longer form a vacuum to pull water into the pump) and then resume delivery without outside attention. The self-priming feature permits the pump to continue to run even when the minimum pumping capacity is greater than the seepage of water.
Portable pumps feature discharge sizes ranging from 1.5 inches to 4 inches and are powered by either a 2- or 4-cycle gasoline air-cooled engine or an electric motor.
Choosing the Right Pump
The two most popular kinds of self-priming pumps are centrifugal and diaphragm.
The agricultural pump and the trash pump both fall into the centrifugal pump category. The agricultural pump transfers clear liquids and dewaters and is popular for turf irrigation and small farming operations. The trash pump transfers water mixed with large amounts of spherical solids. Most trash pumps can tolerate solids up to one half the size of the hose diameter, which makes them useful on construction sites, excavations, drainage ditches, and for septic systems.
Centrifugal pumps use an impeller mounted in a housing called a volute. The engine shaft rotates the impeller at high speeds and creates a vacuum at the center, which in turn pushes water up the hose to the pump. The rotating impeller forces water against the internal surface of the volute, which then directs water to the discharge outlet.
These pumps have a high suction lift that eliminates the need for placing the pump directly at the water source. Centrifugal pumps are designed for water containing up to 10 percent suspended solids by volume and will pass solids up to 1/4th of the hose diameter.
The diaphragm pump is also a self-priming pump; but, instead of an impeller, it uses a heavy elastomer plate of rubber called a diaphragm to form a sealed water chamber. As the diaphragm moves up and down, vacuum and pressure move the water through the pump.
Designed for transfer of water with high abrasive solids, such as mud, sand, silt, and sludge, this type of pump is usually used for industrial maintenance and municipality work, trench and foundation work, and septic systems and seepage.
Unlike centrifugal pumps that rely on water to cool the internal parts, dry pumping will not damage diaphragm pumps. Therefore, seepage in the water that is flowing through the pump does not compromise pump performance.
Using Your Pump
It is important to know “what and where” you will be pumping, and then pick the correct size pump with the correct seals for the fluids that you will be transferring. Remember that altitude will affect performance. The higher the elevation, the less lift there is. Never plan for more than 25 feet of suction lift.
Pump Specifications
Typical Discharge capacities for various pumps are listed below. Alternate brands and types of pumps may have varying discharge rates.
3/4″ Submersible 600 GPH
2 ” Submersible 5000 GPH
2 ” Centifugal 8000 GPH
3 ” Centrifugal 15000 GPH
2 ” Trash 11000 GPH
3 ” Trash 21000 GPH
3 ” Diaphragm 5200 GPH
