Situated along Lake Huron in Michigan, Tawas City is a popular vacation town. While unique in many ways, the city is similar to many other communities in being plagued by frequent pump ragging in its wastewater treatment facilities.

Improper disposal of nonwoven and fibrous materials such as wet wipes and diapers is a multibillion-dollar problem in the wastewater industry: Lift stations regularly require manual lifting and cleaning of pumps. Even if the pumps do not regularly trip out, they are likely to operate in a partially ragged condition, hindering their efficiency.

In Tawas City, crews had to visit up to three times a week to clear dry pit pumps. The problem was compounded because the pumps were located in confined spaces, which meant a team of three people had to be present each time to clean the pumps out while following OSHA safety procedures. This cost significant money and put staff at risk from exposure to raw sewage and sharps.

The city addressed the problem by deploying Real Time Pump Protection technology from DERAGGER to eliminate the ragging issue.

Making pumps smarter

In summer 2018, local representative Kerr Pump & Supply equipped one pump station with DERAGGER+ devices, a technology that combines an advanced power analyzer with a logic and mathematical processor. The technology measures the motor’s raw power signature and understands the torque profile of the pump.

By way of a highly developed algorithm that searches for specific fluctuations in torque, the device can detect when rags catch the pump impeller. Once this condition is detected, the device pauses and briefly reverses the pump in order to dislodge the rags. It then passes the rags through the pump rather than dropping them back into the well or weaving them into a full obstruction. The device does not reverse the pump according to arbitrary timed reversals, and it does not simply wait for a high current setpoint to be reached. Either of these approaches can allow time for rag balls to form. 

The technology can also detect issues such as advanced bearing or seal wear, alerting operators before the equipment fails. In this way, Real Time Pump Protection can greatly extend pump components’ life and can enable teams to plan maintenance in advance.

The city paired the technology with the DERAGGER PRO pump station controller, a simple-to-use, gesture-controlled touch screen made from highly durable glass and aluminum that provides real-time and historical data on the performance of the pumps and the DERAGGER+ devices.

Substantial savings

Since the technology was installed, the city has seen complete elimination of ragging at the pump station. The pumps have not had to be lifted and cleaned even once. They pass the rags along to the wastewater treatment plant screens. With manual pump cleaning eliminated, staff members are no longer exposed to confined-space hazards.

Given that each pump cleaning costs the city at least $300, estimates are that the Real Time Pump Protection on the one pump station has meant monthly savings of about $3,600. This means full payback on the investment has been achieved in just a few months.

“We were coming to clean the pumps as often as three times a week,” says Mike Bocker, operator. “We haven’t had to clean either pump a single time since installing the DERAGGER+ devices. Dealing with ragging was wasting not one, but three people’s time, and that time is now used better elsewhere.”

Documenting performance

An independent study by the Water Research Centre (www.deragger.com/wrcreport) recently found that many lift stations around the world are running partially ragged without the utility realizing it. Operating a pump in a partially ragged condition hinders efficiency, flow rate, runtime, speed and power consumption.

In this WRc study, the DERAGGER+ device was tested on three lift stations that the host utility classified as “nonblockers,” and yet efficiency gains of 7 percent, 15 percent and 20 percent were achieved. The device reduced overall runtime and energy consumption and increased asset life. 

About the author

Graham McIvor is technical director with DERAGGER.