Electric Winch System Helps Plant Screen River Water

Sept. 1, 2010
The Twin Oaks Valley Water Treatment Plant in San Diego, Calif., filters and distributes water to all of San Diego County.

The Twin Oaks Valley Water Treatment Plant in San Diego, Calif., filters and distributes water to all of San Diego County. When the largest submerged membrane water treatment plant in the world called on the Metropolitan Water District in Los Angeles to pipe unfiltered, screened water to the new facility, updating a set of trash racks became a necessity.

Located upstream from the plant, the trash racks provide large-scale screening functionality. After channeling Colorado River water through the racks, the water filters through a much finer mesh traveling screen downstream, then journeys along the pipeline to the treatment facility.

An electric winch from Thern raises and lowers the trash racks for cleaning.

To protect the fine screen and insure properly screened water enters the treatment facility, installing a reliable trash rack upstream to collect larger items was essential. Rather than manual operation, Metropolitan decided to use electric power to raise and lower the trash racks to ensure more reliable cleanout capabilities.

The solution was an electric winch system with two-part rigging and custom drum configuration from Thern Inc., a winch and crane manufacturer in Winona, MN. Because of limited geometry, the installation was a challenge.

"It was a significantly tight installation with limited deck space and a short fleet angle distance," said Justin McProud, an engineer for Thern who oversaw the project. "Plus, we had a high load capacity requirement and required the winch to perform both pull and lift functions."

The custom winch system features a narrow drum configuration for easier mounting on the limited deck space. To supply the required load handling capacity, the two-part rigging feature afforded a load capacity rating of 9,000 pounds each, delivering a total of 18,000 pounds capacity. An epoxy finish was added to protect the winch system in the corrosive environment.

Solving the limited geometry and load capacity challenges, Metropolitan's new electric winch system effectively hoists the trash racks for easier cleanout and prevents debris from damaging the traveling screens downstream. WW

Thern is an exhibitor at the WEFTEC.10 event and can be found at Booth No. 5219

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