Squeaky Clean: Remote-Controlled Dam Washer Gets the Job Done

Cleaning house takes on a different meaning at Tacoma Power’s hydroelectric projects. In the past, when moss needed to be removed from the face of the dams, employees at the company’s seven western Washington dams found themselves in a precarious position: hanging from a safety harness, being lowered down the side of a dam by ropes. Hovering hundreds of feet over water, they pointed a power washer at the wall, getting a face full of mossy backsplash as a result.

Tacoma Power’s dams tower up to 365 feet above the riverbed below. Recently, these employees decided there must be a better way.

Using computer knowledge and mechanical experience, the people who work on the dams came up with an idea that led to the construction of something that has not been available before. They developed an automated, remote-controlled pressure washer, which gets the job done faster, safer and more effectively than washing the surface of these massive dams by hand.

Why do they have to bother cleaning the dams at all? It all goes back to moss. Western Washington’s cool, moist climate is ideal for moss and lichen, which also happen to love the dams’ concrete surfaces.

The Federal Energy Regulatory Commission (FERC), however, said the moss had to go. “A couple of years ago, during the annual FERC inspection, the inspector said moss was becoming an issue and getting so thick, FERC personnel couldn’t properly inspect Mayfield dam,” said Dean McLeod, Cowlitz Hydroelectric Project manager. “We knew that eventually we’d be required to remove the moss from certain sections of the face of the dam so the inspectors could do an inspection.”

This left McLeod to pose a challenge to mechanic Ron Jacobson and electrician Chad Chalmers: Can you create something that will help us with the cleaning?

The dam washer cleans the concrete surface of moss and lichens.
The dam washer cleans the concrete surface of moss and lichens.

How it works

Chalmers and Jacobson went to work in their shop in the Mayfield Dam powerhouse, Chalmers applying his knowledge of computer control systems and Jacobson his decades of mechanical experience.

The two skillfully combined their knowledge and used these materials (at a cost of $4,500) to build the washer:

– Steel framework
– Aluminum carriage;
– Two spray nozzles;
– Two motors (1 horsepower each) that move the spray nozzles up and down and the carriage side to side;
– Touch-screen remote control;
– Wireless computer on the aluminum carriage that receives remote control signals; and
– Variable speed unit that allows the operator to control the speed of the spray nozzles for more effective cleaning.

Because the dam washer was custom-designed and fabricated in-house, design challenges were inevitable. The design, carriage system and programming were altered repeatedly until the design team was satisfied. The utility first tested the device on Mayfield Dam on the Cowlitz River While there were a few problems, the washer did its job, and after some minor modifications, it was ready for prime time.

This is how it works: A crane is used to lower the dam washer over the edge of the dam and position it on the dam face. Nozzles shoot water under high pressure back and forth over the concrete and remove the moss with precision. Using the touch screen control unit, employees control the effectiveness of cleaning by adjusting the speed of the carriage that moves the sprayers across the surface of the dam as well as the vertical travel of the spray nozzles. The weight of the frame keeps it up against the dam.

The spray nozzles are slowed down for areas with thicker moss or sped up for areas with less moss.

“Without a doubt, this was the best solution to the problem,” said Terry Ryan, Tacoma Power’s plant engineering manager. And their work is netting results. So far, the dam washer has cleaned more than 600,000 square feet of concrete on three dams – an area larger than 12 football fields. Workers have to spend considerably less time hanging over the dams, and the work is accomplished much more quickly than the old method.

Each of Tacoma Power’s seven dams has different slopes and curvatures, so the utility is working to customize modifications that will allow the dam washer to eventually fit more of its dams. It has been successfully used on three dams so far.

– By Patrick McCarty, generation manager,Tacoma Power

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