CVA actuator facilitates improved control valve operation in the water treatment industries

Mar 03, 2011

Sewage treatment

Rotork has proven expertise in applying new technologies for the automation of valves, introducing enhanced performance and innovative features. This philosophy encompasses the CVA range of electric actuators for control valves, designed for the exacting demands of process control, specifically in continuously modulating applications.

The CVA range of linear and quarter-turn actuators offers an electrically powered process operator with high resolution and repeatability, programmable fail-to-position options, comprehensive data-logging and non-intrusive set-up and calibration in an IP68 watertight and explosionproof enclosure.
 
In the water and wastewater treatment industries there are many applications where the CVA actuator can assist the solution of the most demanding problems. In a typical example, a wastewater treatment facility in the USA uses a hydrothermal three-way needle valve to control the flow of steam into an anaerobic digester to maintain a constant temperature of 36.9°C (98.5°F), utilising a controlled steam temperature at approximately 93.3°C (200°F).
 
An important requirement of the application is that in the event of a power failure the control valve must shut off the supply of steam to prevent an adverse reaction with the bacteria that treats the sludge.
 
The operator’s first attempt at solving this control issue used an electric actuator with a spring to provide failsafe motion. Because of the constant compression and relaxing of the spring this was not a suitable solution as it resulted in constant loading in the motor. The CVA actuator proved to be the ideal solution. By utilising super capacitors instead of a spring to power the actuator to the desired position on loss of mains power, the CVA provides higher-duty cycles and increased accuracy.
 
In addition to meeting the primary requirements of the application, the CVA also provides the benefits of a built-in data logger, enabling the periodic download of information regarding the behaviour of the valve. This data is useful in managing the operation of the digester and facilitates the scheduling of planned maintenance.
 

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