programme undertaken by South West Water. Rotork actuators were specified in accordance with the company’s framework agreement with South West Water. The programme of modernisation, which involves the majority of water treatment plants in Devon and Cornwall, has been implemented to improve the efficiency of backwashing processes to optimise the operation of existing sand filters. This has been achieved by the installation of Rotork AQ electric actuators on new or existing backwashing valves to precisely control their opening and closing speed profiles. Careful attention to this process prevents any water hydraulic shock effect. South West Water’s process partner Purac is the main contractor for the project at eight filtration plants in Devon. The Rotork AQ actuators are operated by an ABB Kent Taylor three-term controller under the supervision of a Modicum PLC in a control system package designed and installed by Purac. Each day at least eight of the filters are backwashed in a sequence by which the actuators are programmed to operate at a graduated speed profile to shut off the water supply, allow in the reverse wash water and finally bring the filter back on line. The graduated valve opening and closing profiles have been precisely designed to ensure that the risk of hydraulic shocks in the filters is greatly reduced.
