Automated trash rakes with frequent equipment failures to be replaced by a much more efficient new system – all very carefully scheduled for a fast-track completion ahead of the November to June flood season – and then…….. along comes a pandemic.
For the Multnomah County Drainage District No.1 (MCDD) in Portland, Ore., robust pumps and trash rakes are essential.
MCDD, in conjunction with three other districts, operates and maintains flood management systems for nearly 13,000 acres of land along the Columbia Slough and the lower Columbia River. These systems include: 27 miles of levee, 12 pump stations, and 45 miles of sloughs, streams, and culverts.
In recent years, during heavy rainstorms and debris accumulation, frequent equipment failures were causing the existing, automated trash rakes at MCDD’s Pump Station #1 to shut down.
“With the old rakes at the end of their service life, we had the opportunity to invest in better, looking at how we could improve the performance of the pump station,” said Brian Eberhardt, MCDD’s Project Manager. “We also wanted to have trash rakes designed with quicker self-cleaning that would in turn be easier to maintain”.
Randy Lyons, MCDD’s Operations Manager, added: “We were having to undertake far too much supplemental removal of debris, which for six to eight days of the year meant us having to have a two-man team go out on a barge to collect larger debris with an excavator, which apart from taking up valuable time, also raised health and safety concerns”.
Replacing in kind wasn’t an option when Brian Eberhardt and his MCDD team began looking for a new system with mechanical design firm, Murraysmith, and their Senior Engineer, Austin Rambin. A much bigger mechanism with a larger rake head was required to increase efficiency over the previous units, which had a three-and-a-half-foot rake head. Also, a trash rake that could lift 2,000 lbs or more was needed, versus the existing lifting capacity of 1,250 lbs.
“We spoke to operators in our region and went to see them”, said Austin Rambin from Murraysmith. “These included one at a hydroelectric dam and another at a power generating site. The fact that the Lakeside Muhr trash rake was scalable for our required widths was a big advantage, rather than some manufacturers, who could only provide fixed sizes”.
He continued; “MCDD has a very good, experienced team, who certainly know how to maintain and troubleshoot, but when we were considering the design of the system around the rakes, we knew we wanted to improve on the cycle time for cleaning, which, for two traversing rakes on a chain system, was taking half an hour. With five Lakeside Muhr stationary Model T-260 Hydronic T Trash Raking Mechanisms, this cleaning time would be reduced to less than five minutes”.
With the support of MCDD’s Operations team, Brian Eberhardt said: “We confidently placed our fast-track order in November 2019 for delivery by the end of June 2020 – and then of course in the spring of 2020, right in the middle of the manufacturing process of our new equipment, COVID-19 hit”.
“We needed more manpower to do the same job”, continued Eberhardt. “And with the weather not always being predictable, the pressure was high to somehow still achieve the fast-track delivery and installation dates”.
Just in time for the November to May flooding season, the new Lakeside Muhr trash rakes were in place and working by the middle of October 2020.
How It Works
The Hydronic T trash rakes are constructed in galvanized steel and include hydraulic power units (one HPU for each trash rake). Having five individual trash rakes allows four units to remain in operation when one trash rake has to be taken off-line for any reason, such as routine maintenance.
Usually, the trash rake systems are furnished with completed control panels, but, on this occasion, MCDD wanted Lakeside to work with its systems integrator, Industrial Systems Inc. of Vancouver, Wash., to ensure that the SCADA system would operate and control the new equipment.
The trash rack cleaners are designed to initiate an automatic cleaning cycle based upon a liquid level sensor or via time clock operation. The hydraulically‐driven trash raking mechanisms start in a parked position, with the telescoping boom and rake head fully retracted.
Upon activation, the telescoping boom moves outward (away from the bar rack) and lowers the rake head downward to the bottom of the bay floor. With the telescoping boom fully extended, the rake head then moves inward into the bar rack for engagement. Once engaged, the telescoping boom raises the rake head to remove captured debris from the bar rack.
When the telescoping boom approaches the fully retracted position, debris is removed from the rake head via a wiper blade and discharged into an existing trough, which is then transported to a debris pit before being removed by an excavator.
Liz Edgar, Engineer and Construction Lead for MCDD, said: “The installation certainly achieved our goals of reducing maintenance and cleaning times. Protecting downstream properties from flooding has to happen at all costs, so the upgrade has given us a more robust system, with everything moving in the right direction. It’s been a difficult time, but we all pulled together. The MCDD crew was awesome to work with and certainly rose to the challenges”.
