PDAM Tirtawening

Abstract

The drinking water company PDAM Tirtawening has two pipelines that supply raw water to the treatment plant. The pipelines stretch out for 31 kilometers from Chikalong(small nearby town) to the treatment plant in Badaksinga in Bandung. For one of those pipelines the current flow to the treatment plant is well below the design flow. The original design flow of the pipeline is 850 liters per second, currently the pipeline transports roughly 580-650 liters per second. This is not a critical problem at the moment because the treatment plant does not have the capacity to treat and distribute more water, but in the nearby future PDAM Tirtawening wants to increase its capacity and supply more water to the people of Bandung. This means that the supply of raw water to the treatment plant also needs to be increased. From the study it can be concluded that the flow drop was caused by human decisions to throttle the flow, based on the fact that there was severe burst (“explosion”) of the pipeline somewhere in the year 2005. The burst was caused by a water hammer incident, occurring during maintenance. During this maintenance period the water flow was stopped and a water body was standing stagnant in the lower end of the pipeline. When the operators opened valve again at the intake point, to start up the flow in the pipeline, the water mass accelerated downwards towards the stagnant water body below. The air trapped between these two water bodies could not escape in time thereby being compressed causing peak pressures. These pressures where of a much higher magnitude than the pressure which the pipeline was designed for, causing the “explosion” of the pipe. The reason why the trapped air could not escape through the air valves is because they are sealed to reduce the chance of locals stealing water. To avoid air entrapment and thereby reducing the risk on water hammer the following three throttling locations along the pipeline where investigated. • keep regulating the inflow at the intake point at Chikalong. • regulate inflow at the first intersection (OVS1) 3 kilometres downstream of Chikalong. • regulate inflow downstream at Badaksinga at the outflow point of the pipeline. From these three options throttling at OVS1 is preferred. The peak pressures along the pipeline stay well below the design pressure. However, throttling at preset at Chikalong has gone ’sufficient’ looking at PDAM’s standards for more than 25 years already. Regulating at Badaksinga (throttling and closing) is not feasible. Very high pressures and problems with cavitation of the intake valve will increase the chance on pipe bursts and damage to the valve. Also, it is recommended to PDAM to slowly open the valve at the intake point after maintenance in order to slowly increase the volume of the flow. This action will insure that the pipeline will slowly fill up with water thereby giving the trapped air the chance to escape, this will decrease the chance on peak pressures and “explosions” in the future.