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Wastewater plant improves efficiency with centrifugal pump

Supplier: Hydro Innovations
02 July, 2012

For over 14 years the Moe Wastewater Treatment Plant has been effectively and successfully processing sewage.

Located in Gippsland, Victoria, the medium-sized plant serves an equivalent persons population of 22,000. Its average daily flow is five mega litres per day.

Starting in February 2010, the plant's wastewater treatment engineers noticed that its two submersible pumps at the inlet station were blocking up with increasing regularity, making them virtually ineffectual and impacting on the efficiency of the plant.

"Between February and the start of December 2010 our submersible pumps were choking about once a fortnight," said Adrian Harper, Senior Engineer Wastewater Treatment Group, Moe Wastewater Treatment Plant.

"The pumps were no longer capable of effectively handling the increasing flows and rags."

To deal with the problem, the engineers would call in their maintenance contractors to isolate the obstructed submersible pump, lift it using a crane, and then clean it before lowering the pump back into the wet well.

According to Harper the entire exercise was time consuming, inconvenient, expensive and negatively impacted on the plant's performance.

"Between February and December 2010 we spent some $27,000 just on getting the contractors in to clean the pumps," Harper said.

The problem also created OH&S headaches as it required the continual lifting by crane and cleaning of an 800kg submersible pump. The whole process increased the risk of accident when the plant was committed to improving its safety profile.

By about May the situation had become untenable and Harper and his colleagues were keen to find a permanent and effective answer to the choking pump problem.

Impressed with the solutions that Hydro Innovations had exhibited at a tradeshow, the plant invited the company to assess their dilemma and provide a workable option. After exploring the site and the needs of the plant, Hydro Innovations suggested that it consider installing an above ground Gorman-Rupp self-priming sewage pump.

To evaluate Hydro Innovation's solution as well as to explore the pros and cons of a self-priming pump versus a submersible pump with a cutter impeller, the plant initiated an option study. The study confirmed that a self-priming pump would be a workable solution.

"We had never used an above ground, self-priming pump at the plant before, and although we were happy to think outside the box, and the study had confirmed that such a solution was viable, we weren't entirely convinced," he said.

"So we asked Hydro Innovations if we could trial the pump for three months which they readily agreed to because they were certain the pump would meet our needs."

Hydro Innovations provided the plant with a Gorman-Rupp T8A3S-B above-ground self-priming centrifugal pump in December 2010. By mid-December the pump was installed and in use.

According to Garry Grant, General Manager of Hydro Innovations, the Gorman-Rupp T8A3S-B self-priming centrifugal pump is a purpose-built sewage pump that is fitted with an aggressive self-cleaning wear plate.

The wear plate has been specifically designed to handle stringy material [such as rags] so that the pump does not clog.

In addition, if any choking does occur, the pump can be easily and quickly unclogged [with only one person and no crane] via the removable cover plate and without the need to disconnect piping.

The machine's unique collar and adjusting screw allows for incremental adjustments of the wear plate clearance. This design allows users to adjust the clearance between the impeller and wear plate without having to pull it apart and without having to handle contaminated [with sewage] components. Once made, the collar locks in place maintaining the clearance setting. This feature enables operators to keep the pump at peak operating efficiency and also doubles the life of the impeller and the wear plate.

After the three-month trial period, the plant was impressed with the Gorman-Rupp pump's performance and purchased the machine.

"We are no longer wasting money on cleaning the pumps fortnightly," Harper said, "plus, the down time associated with this as well as the inconvenience have been eliminated."

"If the pump does need cleaning the design of the pump lets you do it quickly and of course, its done above ground so we don't have to worry about OH&S issues arising.

"Another big plus with the Gorman-Rupp pump is that if you do get a malfunction occurring in the motor you can just replace the motor. This isn't possible with submersible pumps — if there is a motor problem you have to change the entire pump."

With no regrets about having purchased a Gormann-Rupp self-priming pump, the plant has now purchased a 2nd Gorman-Rupp pump. The plant now confidently runs on two Gorman-Rupp pumps instead of three submersibles.

Harper concluded: "As an engineer I grew up on submersible pumps, but having now been exposed to an above ground centrifugal pump I'd say they have a lot to offer and should be seriously considered as a pump option in a wastewater treatment plant."

Self-priming pump basics – Pt 1: Introduction