Dust-like or dust containing solids are passed into a pressurized system via a lock chamber apparatus wherein a porous filter is provided separating the lock chamber into an upper space and into a lower space. Normally a pressurized gas is passed into the lower space and it is discharged from the upper space during the pressure release phase after passing through the filter. When a predetermined differential pressure is exceeded between the upper and the lower space of the lock chamber because of a clogging up of the filter the filter is cleansed by passing the pressure gas partially or totally into the upper space of the lock chamber so that it passes through that filter in the direction reverse to that during the pressure release phase.