Surge Analysis and Engineering Design for a Somerset Pump Station and its Water Distribution System

Pressure surge, also known as water hammer or hydraulic transient, is a time-varying momentary phenomenon. It happens when the equilibrium of a flow system is disturbed by a status change over a relatively short time period. Caused by either immediate startup or shut-down of pumps, or rapid opening or closing of valves, surge events can introduce large pressure forces and rapid fluid accelerations into a water distribution system, which may result in pump and device failures, system fatigue or pipe ruptures, and even dirty water backflow/intrusion. Therefore, surge protections are extremely important for the design of hydraulic systems. This paper reviews the commonly used surge control strategies that include redesign of the plan and profile of the pumping station and pipeline system; selection of pipes and fittings to withstand the anticipated pressures; identification of proper start-up, operation, and shut-down procedures for the system; and selection and location of the proper control devices to mitigate the adverse effects of surge events. The pros and cons of the control devices, such as hydropneumatic tanks, air valves, surge valves, and pump control valves, are also discussed. A pump station and its transmission/distribution system in Somerset, Texas, is proposed to provide drinking water from the to-be-upgraded Somerset pump station to its serving areas including three different pressure zones: 830, 730, and 790. This project is a part of the San Antonio Water System's (SAWS) district special projects and upgrades to the facility are necessary to support integration of the pump station into the SAWS network. This system includes, but is not limited to, the Somerset pump station and the water distribution network including ground and elevated storage tanks. The system has a design capacity of 5.441 million gallons per day (MGD) representing the maximum hourly demand of the system. Without surge protections, the surge analysis results indicate that the pump and distribution system can have serious downsurge (low negative surge pressure) problems. The goal of the surge analysis is to provide a cost-effective surge protection system to mitigate the potential surge damages. Specifically, downsurge pressures need to be checked and reduced to the minimum impact. Based on the surge modeling results, hydropneumatic tanks and other devices and strategies are proposed to mitigate the downsurge impact. The final simulation results indicate that the surge control strategies will provide reliable surge protections to the pumping and pipe systems.