US Patent 7735515 Valve system

A valve system both controls fuel flow by means of a valve and senses the condition of the valve. The valve is actuated by an actuator via a rotatable shaft. Light is transmitted by a laser diode, via a polarising filter (which is mounted to rotate with the shaft), down the shaft, and is reflected by a mirror which directs the light back up the shaft via the filter to a receiver, which is able to detect different directions of polarisation of the light received. The polarisation of the light received by the receiver indicates whether the valve is open or shut. If no light is received a fault is deemed present. Thus, the condition of the valve is checked directly by means of an apparatus remote from the valve and the fuel.