Suction is the pressure difference between two areas. Pressure balancing takes place when these two areas are connected, causing air to move from the high-pressure area to the low-pressure area.
At the floor tool, suction is weak because of the distance from the motor, and poor swivel joint seals in the hose. The seal between the floor tool edges and carpet is close to non-existent. Suction doesn’t explain dust removal.
We know from experience that the best cleaning performance is provided when the vacuum cleaner filters are clean and the airflow is high.
We also know when we spot clean, we do a better job using a crevice tool, but airflow with a crevice tool is 35% less than the floor tool. It seems neither airflow nor suction adequately describes the dirt removal process when vacuuming.
Dust removal by a vacuum cleaner is due to pressure placed on the dust particle by airflow. This is called velocity pressure. Velocity pressure has a positive value. Table A shows the velocity pressure produced by airflow at a floor tool and crevice tool.
|Air Flow (l/s)||34||22|
|Aperture Area (mm2)||1964||284|
|Velocity at the Tool (km/h)||62||279|
|Velocity Pressure (Pa)||180||
The velocity of air at the crevice tool is 279 km/h and the velocity pressure placed on a dust particle is 20 times higher than the velocity pressure placed by the floor tool, but it’s impractical to vacuum a large area with a crevice tool.
Removing dust from the carpet using this method doesn’t provide a high level of cleaning. Dust particles are entangled in the carpet fibre, and velocity pressure alone isn’t sufficient to remove all of them. Mechanical agitation provided by a turbo brush or electric brush, aid dust disentanglement and provide better dust removal. We found from our tests that the turbo brush was 2-3 times more effective in removing dust from the carpet, and an electric-powered brush was 5-6 more effective in removing dust from the carpet, than a low-profile floor tool. These tools are also less demanding on the vacuum cleaner because they maintain higher airflow which is essential for cooling the vacuum motor.