Grinder pumps are designed to reduce the solids typically found in wastewater into a slurry that can be pumped under high pressure through small-diameter piping. Small grinder pumps, 2 hp or less, are commonly used in residential, light commercial or light industrial applications. These may be necessary in areas of low-lying terrain or where long, flat lateral runs of piping are required, or as a solution for mitigating clogging due to troublesome solids. Larger grinder pumps, up to 15 hp, are commonly used in commercial or industrial applications where a more robust solution is required for managing solids.   

Performance

Small grinder pumps, 2 hp or less, have a typical performance range of 130 to 200 feet of head pressure, with maximum flows between 15 to 55 gpm. Large grinder pumps, up to 15 hp, can achieve heads up to 250 feet with maximum flows exceeding 150 gpm. Typical grinder discharge sizing is between 1.25 and 3 inches.

Grinding technology

There are two main types of cutters used for grinding mechanisms: axial and radial. 

Radial cutters are a more traditional style featuring a sharp shredder ring with several channels around the radius. Inside the shredder ring is an angled spinning blade. As items enter the pump, the blade paired with the sharp channels in the shredder ring cut down any item passing through the components. With low horsepower pumps, radial cutters can be more susceptible to clogging or jamming on items such as wipes or other flushables. It is especially troublesome if the pump stops running while in the process of cutting a solid and then tries to restart. Radial cutting technology is commonly used with higher horsepower pumps, which offer higher torque — making them less prone to jamming.

Axial cutters feature a spinning blade which is mounted beneath a slotted suction plate. This cutting mechanism acts similarly to a cheese grater and takes nibbles out of solids as they come in contact with the cutter and the plate. By nature of this design, solids are cut into a slurry before entering the volute, reducing the jamming risk seen in radial cutter designs for low horsepower grinder pumps. 

Configurations

In a typical grinder application, you will find two different basin configurations: a pump on a stand or a pump on rails. Rails are the more traditional installation and allow for grinder pumps to be easily pulled in and out of a basin with a fitting that locks into a metal rail in order to slide down the basin and into place. A pump on a stand simply sits at the bottom of the basin and either has a flexible discharge hose or hard PVC piping that connects it to the basin discharge.

These installations always require a check valve and shut-off valve to ensure the station can be isolated from the pressurized line it is hooked up to. Basins (sometimes referred to as wet wells) are either HDPE, fiberglass or in rare cases, concrete. Many grinder pumps feature a level control, which notifies the pump to turn on or off when the liquid in the wet well reaches a certain level. These are most commonly float switches but could also be a pressure switch.