Representing Check Valves in a Force Main Water Hammer Model

Check valves, depending on their closure characteristics, may introduce significant transient pressures after pump shutdown. Therefore, appropriate representation of these devices in water hammer models is important for simulating accurate transient response. However, the lack of check valve closure characteristics data makes modeling of these devices prone to inaccuracy. This paper investigates the calibration of a water hammer model where check valves are present. The model was developed for a force main system located east of Brevard County, Florida, using Pipe2000. The system consists of approximately a 21.3 km and an 8 km long two parallel force mains consisting mainly of 508-610 mm ductile iron and polyvinyl chloride pipe sections. A high speed data acquisition system was used to capture steady state and transient field pressure traces during normal pump shutdowns. The model was calibrated and validated to match steady state and transient field-measured pressures. Results showed that check valves can be modeled accurately by: (1) recording shutdown-induced field transient pressures at the pump station where check valve is installed, and (2) conducting sensitivity analysis during which, check valve closure time is adjusted until the predicted transient pressure traces are mapped into field-measured pressures. Inaccurate modeling of check valve closure characteristics was found to significantly over or under predict pressure spikes following pump shutdown. Excluding the check valve from the model when flow reversal is not enough to activate the valve closure in the field was found to be appropriate to avoid model instabilities and predict accurate pressure responses.