Vacuum filtration is more efficient and faster than filtration by the gravity method. But the set up of the vacuum filtration must be precise. Vacuum filtration is done under very reduced pressure hence there should be no gaps around the edges of the filter paper.
For a vacuum to be effective there must be no hole or gap in the equipment. Under vacuum conditions air is removed and the pressure is lowered. If there is gap then air would be continuously supplied and it would be difficult to remove air completely.
