For nearly 40 years, the Del-Co Water Co., whose motto is “Quality on Tap,” has been treating, clarifying and softening extremely hard well and surface water for its customers in Delaware and Morrow counties in central Ohio. To assure water quality consistency for all their customers, treatment techniques are the same at all four Del-Co plants:
- Raw water flows to single-stage solids contact basins where clarification and softening occur. Raw water hardness can vary from 180 mg/L in surface water to 350 mg/L in groundwater;
- Lime softens water to 105 mg/L;
- Settled solids are transferred for further processing;
- Carbon dioxide is added to lower the pH, ending the softening process and stabilizing the water, a process that takes approximately four hours;
- Water passes through sand filters to further remove small particulates; and
- Finally, chlorine disinfects water prior to consumer use.
Problems
Damon Dye, plant superintendent, and Chuck Penry, maintenance supervisor, had experienced several problems with the air-operated diaphragm pumps they were using at two stages: moving sludge from clarifying tanks in the basement to holding tanks for further settling; and removing settled sludge from the bottom of the holding tanks as needed, usually daily. The pumps were not responsive to the varying slurry densities and flow rates. Air valves and check valves often fouled and failed, resulting in frequent down time. Further, the pumps were so noisy in operation that personnel complained that they could not hear each other talk.
Dye, Penry and their team consulted with a local fluids handling firm who told them about seepex progressive cavity (pc) pumps. Seepex then recommended its range “BN” (block) pumps to handle the abrasive lime slurry being pumped from the tanks.
In operation, a PC pump’s single helix rotor rotates within an elastomeric double helix stator to form sealed cavities that progress from the suction side to the discharge end of the pump. The continuous seal between the rotor and the stator helices moves the fluid steadily at a fixed flow rate proportional to the rotational speed of the pump, and independent of pressure fluctuations that can result from varying densities and viscosities of conveyed product.
Del-Co is pleased with its pc pumps, which they have been using for over six years. Not only do the pumps handle fluctuating flows with ease, but they also are able to pump the slurry directly via 6-in. piping a full mile from tank to destination. When needed, pump maintenance takes only minutes, noted Lonnie Evans, assistant maintenance supervisor.
PC pumps are less complicated and are more energy efficient than air-operated diaphragm pumps. Eliminating check valves and air valves alone results in a much less complicated and problematic piece of equipment.
It is always a good idea to avoid air power when installing equipment for permanent use, and instead use dedicated electric motors and switchgear. Capital and installation costs may be higher, but the energy and maintenance savings are so great that a permanent electric installation usually has a payback of a few months when compared to operating process equipment with compressed air.
