"Zero failures" for power station's electro-hydraulic control valve solution
25/08/2005
Protracted problems with pneumatic control valves have been successfully eliminated by the introduction of electro-hydraulic alternatives at the Scottish Power Longannett Power Station in Clackmannanshire.
The new equipment - comprising ball valves and Rotork Skilmatic actuators - has been installed to control water levels in direct contact heater and condenser plant areas.
Derek Duncan, C & I Engineer at Longannett explained: "Historically the air system at the site has not been of good quality, causing problems which increased following the introduction of a new distributed control system (DCS) in 2000. The SMART positioners retrofitted to pneumatic actuators at that time are particularly intolerant of moisture in the air supply. It was therefore decided that the best way forward would be to adopt a new approach to the actuation.
In discussion with various suppliers a fully modulating actuator with a soft seated ball valve became the preferred option".
The Rotork Skilmatic electro-hydraulic actuator and ball valve combination was recommended by specialist actuation service provider Exeeco, a company with a long and successful history of supply and maintenance at Longannett. The Skilmatic actuator provides the simplicity of electrical operation, combined with the precision of hydraulic operation for modulating or fail-safe applications. The actuators operate directly from an electrical supply and control signal, without relying on a pneumatic supply.
The new actuated valves were installed during a major outage on Longannett Unit 2 in the summer of 2004. Derek Duncan observes: "To date this system has run on auto with zero failures and all concerned are very satisfied with the outcome".