A tourist hotspot, Hermanus is in a water scarce area. To alleviate the perennial water shortage, the water supply authority of the Overstrand Municipality decided to upgrade the Preekstoel water treatment plant built in 1974 and add more automation to increase efficiency.
Coen Pretorius, sales engineer at Festo Cape Town explained that the Overstrand Municipality decided as part of the modernisation measures, to replace electric actuators for opening and closing butterfly valves or ball valves with pneumatic ones. Festo was able to convince the authorities that pneumatic automation technology could reduce investment, installation and operating costs in comparison with electrical installations by more than 50% in some cases.
Pneumatic drives remain maintenance-free for the duration of their service life. Since process valves are irregularly actuated in water technology, residues or build-ups can occur that result in significantly higher breakaway torques. The overload protection of pneumatics is an important feature in this situation. If the drive comes to a standstill, the pressure can be easily increased at the pressure regulator to be able to apply more force, eliminating any need for costly maintenance.
The Overstrand Municipality replaced the electric actuators at the filter basins with pneumatic actuators and positioners from Festo and installed control loops with flow and level sensors. The butterfly valves and slide valves in the sand bed filters and ultra-filtration plants of the Preekstoel water treatment plant are now equipped with type DLP and DAPS pneumatic actuators.
Copac linear actuators or DLP for short are the ideal solution for shut-off, safety and control slide valves, acting directly on the slide gate and ensuring that various positions can be approached accurately. The high corrosion resistance of the actuators allows their use without any problems out in the open in coastal conditions.
The sturdy DAPS quarter turn actuators control ball valves and butterfly valves with various media flows and an angle of rotation that is limited to 90°. The torque is generated via a scotch yoke mechanism, which helps to overcome the valve’s high breakaway torques.
The decentralised valve terminal is the core of pneumatic systems in water technology. Located in the vicinity of the process valves, it is ideal for fast and simple automation solutions featuring the optimum interaction of process valves, pneumatic components and electronic components. The valve terminals have a modular configuration based on the number of process valves, while the fieldbus provides the system with a single, clearly defined, standardised interface between the controller (PLC) and the valve terminal. Extensions or modifications can simply be made at control level, without having to replace the hardware.
The butterfly valves are controlled by MPA valve terminals, providing information about the filter’s current status by determining its fill level, differential pressure and flow rate. The PLC controls the valve terminal if a filter needs to be rinsed. The valve terminal is configured based on the number of pneumatic drives, limit switches and measuring instruments.