Grinder Pumps & the Evolution of Pressure Sewer Systems

Gravity sewer systems are the primary method used by municipalities to transport residential sewage waste to a collection or treatment facility. Gravity sewers use the force of gravity to push fluid through networks of large sloping pipes to the sewer main. For all sewer technology, fluids require a minimum flow velocity to keep solids suspended. When solids settle in a wastewater system bad things happen, such as blockages or odor problems.To get more news about bryson pump, you can visit brysonpump.com official website.

States and municipalities publish design criteria which dictates the standards for the required minimum flow as well as the minimum pipe diameters and minimum slopes to accomplish these flows. What this means for contractors is that a sewer main must be installed deeper than the discharge lines from each source connected to it. Lift stations can be used to pump fluid to a higher elevation, which allows the sewer main to be located closer to the surface; however, lift stations can be expensive to construct and more expensive to maintain. Overall, the construction of sewer infrastructure requires extensive digging of trenches, which is costly and has an environmental impact. These challenges are more difficult in areas where water tables are high or the landscape is hilly, rocky or flat.  Pressure sewer systems were designed in the early 1970s as an alternative for applications where gravity sewer systems were less feasible or economical. It provided a means to combat difficult terrain and reduce the upfront cost of slow buildout projects or developments. The primary differences between conventional gravity sewer systems and pressure sewer systems are in the piping network and the reduction of solids size in wastewater at each residence. Pressure sewer systems utilize a network of grinder pumps to transport wastewater through small diameter pipes, directly to a sewer main, lift station or treatment system. A grinder pump is a submersible pump designed to reduce particulates in a waste stream into a fine slurry using a grinding mechanism. In order to overcome challenging terrain, pipes are installed just below the frost line and follow the natural landscape. The pumps must operate with high pressure and limited flow when compared to a gravity system. There are two basic forms of grinder pumps that can be used in pressure sewer applications—progressive cavity or centrifugal. With a progressive cavity grinder, pumping is performed by a specially shaped, stainless-steel rotor that turns within a multilobed rubber stator. The friction developed between the two components develops the pressure used to transport fluid. Centrifugal grinder pumps use a vortex impeller to create pressure and flow. As the impeller rotates, it creates a vortex in the pump casing that carries the slurry outward from the volute chamber to the piping system.

History of Progressive Cavity Grinder Pumps in Pressure Sewers Originally, progressive cavity grinders were the pump of choice for pressure sewer applications due to their ability to pump with a narrow range of flow (10 to 15 gallons per minute [gpm]) at high head pressures (up to 150 feet). Progressive cavity pumps are not self-limiting with respect to pressure; as the system volume increases, so does the pressure. If the system pressure exceeds the shutoff head pressure for the pump, the pump will continue to try to overcome back pressure until something breaks down. The breakdown could be as simple as a tripped thermal sensor or as serious as a broken line or damaged pump. At the least, the increased pressure leads to increased wear. Since these pumps operate by way of friction, the components of the pump are experiencing continuous wear.

Wear is accelerated with high pressure, high flow, long run times or the addition of grainy particulates in the waste stream, such as sand and dirt. The pump stator of a progressive cavity grinder is both the highest wear item and one of the more expensive components to replace, making repair or premature failure costly.