The impeller of the coolant pump to impose a sleeve, which seems to be at least the most efficient way to put their promotion to zero, although it continues to be driven and thus down to storage or belt drive consumes no energy currently. The electrical connection needs at this stage also little energy, with a warm engine no.
The picture shows the two positions. With the valve a chamber is closed which is flowed through by coolan. The necessary pressure is built up by a small piston driven by a wobbling disk. This presses the sleeve against a spring upwards (picture below). In the case of an electric or electronic mistake the spring remains released and the sleeve stays at its lowest point. The pump is always conveying.
Exciting is the question of how the pressure passes from the working chamber of the pump to the of the piston. Of course, there should not drain too much coolant there, otherwise the delivery of the pump suffers. If necessary, you need to increase the next picture to realize the fine holes in the wobbling disk.
Which brings us to the demand on the coolant. You guessed already, it must not contain any solid or pasty parts. Basically, now mixed with distilled water and additionally added silicate, the compensation tank even a small bag with filling for lifetime. Silicate prevents precisely the deposits that could block such small holes. 01/16