Hoovers simply use a centrifugal blower, which achieves a high flow rate but has nothing to prevent a back-flow if the pressure difference across the blower becomes enough to oppose the fan.
Laboratory vacuum pumps are proper pumps rather than blowers, they have a system of pistons and valves so that a volume of gas is removed from one side and pushed out at the other. These have a much lower flow rate than a hoover blower, but work down to a much higher pressure difference. They stop working when the valves and pistons can no longer seal adequately or the working volume simply isn't capturing any more gas molecules.
Ultra-high vacuums are created using exotic molecule capturing processes which require a pretty good vacuum in the first place before they start working.