Rotork Profibus actuators control the flow at Wessex Water’s

Published: 25th September 2009 | Issue 8

Paul Roberts from Wessex Engineering and Construction Services and Tony Scott from Rotork discuss the actuator control system and installations on the dissolved air flotation tanks in the new Maundown building.

Wessex Water is installing Rotork intelligent electric valve actuators throughout a £25 million project to improve the quality of water supplied to over 200,000 customers in central Somerset. Maundown water treatment plant was built in the 1960s and first extended in the early 1970s. The site, which treats water from Wimbleball and Clatworthy reservoirs, is now being entirely redeveloped to further improve the quality of drinking water, upgrade the water treatment facilities and meet increased peak demand for water in the area.

Under PLC control, Profibus-enabled Rotork IQ and IQT electric actuators will operate penstocks and butterfly valves to control the flow of water and sequential backwashing operations throughout the new state-of-the-art treatment plant, comprising raw water screening, dissolved air flotation, rapid gravity filtration and granular activated carbon treatment followed by chlorine contact tanks. As well as increasing the treatment capacity to 82.4 Ml/D, the improved treatment processes will overcome taste and odour problems caused by increased algal blooms in the local water sources resulting from changing weather patterns.

The work at Maundown is being carried out by Wessex Engineering and Construction Services, utilising specialist sub-contractors and the existing framework supply chain management system for materials. The controlling software and SCADA programme for the new treatment plant has been written by Wessex Automation, who have standardised on drives, valves, actuators and instrumentation in all areas. Instrumentation is being supplied by Endress & Hauser, who are also integrating all the process elements into the Profibus control system.

Wessex Water has an enviable reputation for environmental awareness, which is evident in every aspect of the Maundown scheme. Flow through the treatment processes is propelled by gravity, without the assistance of energy consuming pumps, whilst en-route from the reservoirs the flow into the works operates a turbine to supplement the supply of electricity to the site. Additional renewable energy will be provided by solar panels to complement the site’s wood pellet burning heating system.

The new building has been designed with a sedum (green) roof, providing excellent all-year-round insulation and a natural habitat for wildlife, as well as helping the site to blend into its rural surroundings. All the water from the roof is collected with the site’s surface water and stored in a dirty wash water tank, from where it is channelled into the head of the treatment works.

Rotork has supplied more than 200 actuators for the Maundown project, which has the support of the Government’s Drinking Water Inspectorate and is due to be completed by the end of 2008.

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