Engineers are continuously searching for more creative ways to design and complete infrastructure and other projects, says international engineering and project management consultancy Royal HaskoningDHV, which has, in a joint venture with Knight Piésold and Naidu Consulting, completed the Ashley drive break pressure tank (BPT), in KwaZulu-Natal.
Royal HaskoningDHV design engineer Darren van Rooyen explains that the varying flow and pressure conditions at the BPT required innovation in the design and overall construction of the system.
The Ashley drive BPT has been designed for a through-flow capacity of 400 Mℓ/d in the year 2035. It limits water pressures in the Western Aqueduct pipeline which is supplied from the Umlaas road reservoir at its highest point between Pietermaritzburg and Durban. The pressure in the Western Aqueduct has to be ‘broken’ at various points so that the potentially destructive energy in the pipeline can be safely and economically controlled.
Van Rooyen explains that, under normal steady-state conditions, the Aqueduct works like a well-behaved lazy river. However, when there is any change, such as an increase or a decrease in water demand, the inlet to the BPT must react. If the reaction is too fast or too slow, potentially catastrophic overpressure in the upstream pipe or overflow from the BPT may occur.
He points out that there has previously been theft of strategic installations, which has had a major effect on service delivery, and there was a specific requirement for an automatic, hydraulically controlled backup solution in the event of a power outage.
Sleeve valves were selected for the inlet control because of their noncavitating characteristics under high-flow and high-pressure conditions. Float controlled automatic globe valves were provided as backup to close sequentially in a power outage or fault condition when the water starts to approach the overflow level. Even before the globe valves start to close, an alarm will be sent to the water department’s control room and maintenance staff dispatched to attend to the fault condition.
Construction of the Ashley drive BPT started in January 2014 and was completed in November 2015. Van Rooyen explains that local contractors and labour were used as much as possible in the construction of the BPT and the environmental impact of the project was monitored against a comprehensive environmental management plan to keep the impact to a minimum.
Other KwaZulu-Natal Projects
Royal HaskoningDHV has also recently completed the Richmond pumpstation (RPS), in KwaZulu-Natal. This pumpstation, which forms part of the new water supply to Richmond, includes two 1 750 kW pumps driven by vari- able frequency drives to transport water up the hill to a new balancing reservoir before gravitating to Richmond.
Owing to the varying demands on the system, the pressure at the pumpstation can vary by up to 60 m and pump speed is con- trolled by a complex operating philosophy programmed to protect the pumps from cavitation and the pipeline from transient pressures while maintaining the design flow.
Royal HaskoningDHV has a full spectrum of multidisciplinary engineers working on projects such as the Ashley BPT and the RPS, who are looking for new techniques and innovative ways to decrease the time and cost of creating new infrastructure.