How does a starter sprag clutch work ?

[fraserdog]

In relation to another post of mine i want to get my head around a sprag clutch works,i know centrifugal force engages it when the starter motor spins but does it stay engaged while the engine is running and drop out when the engine stops? If so how does the starter motor disengage? I am a mechanical engineer by trade so understand the principles but without one in my hand or an exploded diagram to go by i was just wondering what makes a sprag tick 

[Mustang]

a triumph sprag is similar
99% of time its the spring that goes bad .......................like this ktm did