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Robert Dohm knows a lot about fluid-handling pumps. He spent much of his working life as a pump mechanic at a prominent chemical company’s West Virginia plant. The large pumps had to function reliably in some of the most caustic process environments imaginable. Dohm recalls every pump at the specialty chemical plant as specifically engineered to withstand the process flows, from their metal casing to the seals, coatings, bearings and controls.
Even with an aggressive, proactive maintenance program, however, some pumps still would fail. That gave him job security for 29 years, he said.
Now 77, Dohm retired 20 years ago to his “dream home,” built in a new residential development along Lake Wylie, a 13,400-acre reservoir located in both North and South Carolina. He built on one of the initial 15 waterfront homesites situated atop a virtually impermeable former gravel pit.
“At the time we built the house, there was no connection available to a community sewer system,” Dohm said. “Because the rocky ground would not percolate, the developer had bought a more porous site large enough to install a common septic tank with suitable soil and had an engineer design a low-pressure system to accept the raw sewage there from 15 homes.”
According to Dohm, the design was changed in favor of each homeowner installing an individual septic tank to accept the sewage before it passed through a grinder pump, which was then pumping effluent. Unlike the raw sewage, the greywater built up hydrogen sulfide gas that attacked the pumps, which were not designed to withstand that kind of operating environment.
Frequent Pump Failures
“We went through several pumps in the following years,” Dohm said. “Neighbors also experienced pump failures—probably 17 pumps in all.
“My original pump lasted only four years and wasn’t worth fixing when they pulled it,” he explained. “It was replaced at no cost by the supplier, but it cost us $2,000 to replace a third pump a few years later. Even that pump had developed loud bearing noise, so I had to replace or repair it. At that time, I decided to replace it with a Flygt pump.”
By then, Dohm and the other homeowners had connected to a recently installed municipal sewage collection grid. Dohm bypassed his septic tank, allowing the raw sewage to pass directly through the grinder pump on to the collection line, and then to the municipal wastewater treatment plant.
His expertise with pumps once again came into play during the fourth pump replacement at the beginning of 2012.
Flygt progressive cavity grinder pumps from Xylem Inc. are suited for waterfront, remote and low-lying locations. Typical residential applications are individual homes, a small network of residences or an apartment building.
Before it was selected, however, the pump had to pass Dohm’s scrutiny, developed over decades of working on pumps at the chemical plant. Dohm was impressed by the simplicity, durability and ease of installation of the Flygt unit.
“I liked the pump’s design features,” he said. “Unlike the earlier pumps, the electrical controls are not mounted inside the new pump, but [instead are] in a weatherproof box outside the sump, and therefore clear from possible flooding in the sump.”
By moving the controls out of the sump, the existing wet well/dry well configuration was converted to a complete wet well that increased the storage capacity by 40%. The work also changed the method of level control from a built-in pressure transducer to a level stick that allows for a lower maintenance alternative, without vents or breather exposed to potential flooding.
“We were able to use the same basin and eliminate any digging,” Dohm said. “The entire process, including the rewiring, lasted only three hours.”
Dohm believes the chronic pump failures are finally behind him. “There are about 30 remaining lots to develop here, and two-thirds will probably need to pump their sewage to the collection line,” he said. “Some will probably want to see our system. The elimination of individual septic tanks and our connection to the municipal collection line should prevent what we experienced and make the lots more marketable.”