Pump Addition Fixes Tank Problem

Abstract

The distribution system for the City of Westerville, Ohio, includes two pressure districts and three elevated water tanks. The first district includes two water storage tanks. Otterbein tank, the system's original tank, holds only 300,000 gal. Pointview tank, constructed later to meet increased system demand, holds a significantly higher volume of water—1.5 million gallons. The hydraulic gradient of the overflow on the Otterbein tank is 9 feet lower than the overflow of Pointview tank. Pointview was designed with an elevation difference to increase distribution system supply and pressure. The Otterbein tank uses an altitude valve to shut off the flow of water to the tank as it reaches overflow level. When distribution system pressure drops, the altitude valve opens and lets water out of the Otterbein tank. In order to drop distribution system pressure, we had to lower the Pointview tank considerably and shut off the plant's high‐service pumps. When demand peaked during the summer, it was not prudent to lower the tank level for fear of a resulting shortage of finished water. At the same time, there was concern about the Otterbein tank water becoming stagnant. One option was to take the tank completely out of service. However, we ruled this out because we wanted to maintain as much elevated storage of potable water as possible. The Westerville Water Plant Mechanical Department constructed a system that pumps water out of the Otterbein tank while allowing the altitude valve to continue working normally. The new system, which still employs an altitude valve to fill the tank, uses a pumps to lower the tank level.