Control system in wind turbine blades

The invention relates to a wind turbine blade with devices for modifying the aerodynamic surface or shape of the blade. The position and movement of these devices are controlled by a pneumatic actuator powered by pressure from a pressure chamber connected to the actuator via a valve system controlling the powering. The valve system in return is operated by a control unit conveying control signalsto the valve system via a signal communication pathway. The communication pathway may comprise a power link or pressure tubes with a liquid or a gas. In one embodiment the gas used is of a lower molecular weight than 28.9 kg/kmol and thereby lower than air, whereby the speed of the pressure signals being sent from the control unit is increased and thereby the operational speed of the aerodynamic devices. The invention further relates to a wind turbine comprising a tower, a nacelle mounted to one end of the tower, and a rotor with at least one wind turbine blade according to the above.