Addendum: Have the part now 1 week add operation. After completion of the actual filling it hissed back and re-- permanently. Reason: Apparently seals the blocking flap not completely. Now have the amount increased over the level setting, so by a higher water level in the cistern more pressure on the float comes, who is responsible for the complete closure of the water supply. At the moment it works - will watch it on.
Addendum II: It hisses continue. Not after each filling - but sometimes it just like that, without that any action has been carried out previously. This part goes back!