A valve shutter is fitted in a channel and is adapted to be shifted, between a valve-opening position and an intermediate position facing a seat provided in the valve body, through rotation around a transverse axis, while the channel is set under still water conditions. The actual fluidtight application of the valve shutter against its seat is ensured by the pressure of the upstream water when normal flow conditions are restored. This dual movement is possible due to the fact that the shutter supports or bearings are resiliently or pneumatically held in position with reference to the valve body.
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