Improved pump hydraulic design cuts blockages to nearly zero

Overview_TEXT

Overview

Redesign is a ‘stroke of genius’ according to service technician at regional Danish wastewater treatment company.

 

The situation

Palle Tækker drives his truck carefully through the narrow, cobblestoned streets of Ribe, Denmark’s – and Scandinavia’s – oldest town, from 700 A.D. He parks by a small grassy park at Ribe’s harbour, Skibbroen. “We’re in the old part of town, so we have to be as invisible as possible,” he says. 

Previously, Palle and his service colleagues were spending too much time visiting this area. Palle is a wastewater service technician at DIN Forsyning in Ribe. He opens a wooden lid in the park and starts down a ladder to an underground, dry-mount pumping station. This is one of the main pumping stations in Ribe, pumping 1,500 m3/day in dry weather and up to 7,000 m3/day in winter and wet weather.

Up until six months ago, the service crew had to visit this pumping station at least twice a week. One of the pumps kept jamming. 

“We had a lot of problems with pump blockages,” he says. “The pump wasn’t blocked, but it couldn’t operate. We got a dry-running alarm. It might just be a small rag or a sanitary napkin or a wet wipe. They used to stop the pump. It didn’t take much. The pump is also frequency-controlled, so the starting torque wasn’t high.”

What was odd was that this was happening on the Grundfos SE 7.5 kW pump with thenewer, energy-efficient S-tube channel impeller. The other two pumps in the pumping station also had channel impellers, but of an older, less efficient type with different hydraulics. DIN Forsyning had installed frequency converters on all the pumps in order to save energy. The newest pump began blocking about six months after installation. 

“We had to come out and dismantle the pump up to two times a week – without there being a blockage,” he says. “As soon as the pump was lifted, the material was loosened and we could run the pump again without any problem.”

DIN Forsyning began to consider replacing the pumps with another type. Palle called Grundfos. Grundfos sales engineer René Møller Pedersen investigated the installation together with Palle, then took data and observations back to the company.

 

The solution and outcome

Grundfos suggested that the pump could benefit from a different type of wear ring. The company offered a modified design that improved the reliability immediately. 

“It was an easy fix with the different wear ring design,” says René Møller Pedersen, Sales Engineer at Grundfos Denmark. “It is a good solution in applications where the composition and content of the wastewater creates problems.”

Palle Tækker and his crew were happy. “It was a stroke of genius,” he says.

In the half year since DIN Forsyning in Ribe installed the new wear rings on the SE pump, the stoppage problem ceased.

“We haven’t had the problem with the new system,” says Palle Tækker. “We have had, however, a single stoppage where one could say it would have happened anyway. A large rag got stuck, and it’s normal to have a pump stoppage of that kind.”

DIN Forsyning avoided needing to replace the pumps. The time savings on manpower for visiting the station, lifting the pump to clear the blockage and starting it up again amounts to an hour and a half per visit. With at least two times a week, that’s three hours a week of saved manpower. 

“Now we can do other things in those three hours,” he says. “In terms of efficiency, we gained a lot. This solution is superb. If there’s a problem with blockages – and that’s of any kind – then it’s worth considering switching to this type of wear ring.”

“Considering that we thought about replacing the pumps, and that we’re very pleased with it now, we saved a lot by just replacing the wear ring. That’s saved us a lot of time. These pumps don’t come cheap. It was the perfect solution for us.”


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Topic:

Solving blockages in wastewater pumps

Location:

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Ribe, Denmark

Company:

DIN Forsyning water and wastewater utility

different wear ring design could help in installations
Grundfos determined that a different wear ring design could help in installations like Ribe’s with particularly troublesome wastewater composition and content.
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