Why Good Vacuum Cleaners Don’t Suck?

September 14, 2022

How Vacuum Cleaners Work

A vacuum cleaner is a container with inlet and outlet openings, housing a motor coupled to a specially designed fan blade. The motor with the fan, is sealed between the inlet and outlet openings. When energized, the motor fan rotates rapidly and reduces the pressure on one side of the fan blade creating airflow from the pressure imbalance. Air flows from the high-pressure inlet side of the fan blade to the low-pressure exhaust outlet. How Do Vacuum Cleaners Clean? When using a passive floor tool for vacuuming carpet, the ability to remove dust depends on the air velocity at the carpet and floor tool interface. Air velocity applies dynamic pressure to the dust held by the carpet fibre to dislodge it. Higher air velocity dislodges the dust more easily because it applies greater pressure. The scientific explanation of velocity pressure, also known as dynamic pressure, and its measurement is explained in the video link below, What is pitot tube? 3D Animation ( Stagnation and Dynamic Pressure )

Note: Applying the Bernoulli principals mentioned in the video to a vacuum cleaner, the fluid is air, and the static pressure at the nozzle opening is zero since it’s at atmospheric pressure, therefore at the nozzle opening we only have velocity pressure. Design of Vacuuming Tools The combination floor tool shown in the photo below is an example of how the design of the floor tool sole plate increases air velocity. The sole plate has a shallow depression that expands towards the inlet. The narrow aperture created at the sides when in contact with the carpet, increases the air velocity which improves dust removal. Tapering the depression towards the inlet opening reduces airflow losses. The rear depression is a backup for any dust missed while vacuuming. The raised sections on the sole plate help seal the airflow channels and aid in maintaining air velocity.

The combination floor tool provides excellent dust removal and is capable of vacuuming heavy objects such as screws and small coins. The disadvantage is that the smaller inlet opening on the floor tool used for increasing the air velocity also reduces airflow which cools the motor, and this increases the risk of motor overheating. When it comes to vacuuming in-ground dirt from carpet, you can’t go past using the Crevice Tool. Table A compares the performance of the EZ2GO floor tool and Crevice Tool. When using the Crevice Tool, the velocity pressure at its nozzle is 20 times higher than that of the EZ2GO floor tool due to the smaller nozzle aperture. Dirt removal is proportional to the velocity pressure at the aperture area of the nozzle. In this example, the Crevice Tool is ideal for spot vacuuming in-ground dirt from carpet, but the small nozzle size makes it impractical for vacuuming large floor areas. Table A

Conditions

Floor Tool

Crevice Tool

Air Flow

34 l/s

22 l/s

Aperture Area

1964 mm2

284 mm2

Velocity at the Tool

62 km/h

279 km/h

Velocity Pressure

180 Pa

3604 Pa

Output Power

6.12 W

79.29 W

What is Suction Power? Suction Power is the output power of the vacuum cleaner. By knowing the output power, we can calculate the motor efficiency.

Output Power (W) = Total Pressure (Pa) x Air Flow (m3/s)

Efficiency (%) = Output Power (W) / Input Power (W) x 100

From Table A, the increased power generated at the Crevice Tool is from increased air velocity, and not from greater input power. The input power is lower when using the Crevice Tool because less air is moved by the vacuum motor e.g., at 34 l/s airflow the vacuum motor moves 1 kg of air in 24.5 seconds whereas, at 22 l/s airflow, it moves 0.65 kg of air in the same time. In practice, it is doubtful that any vacuum cleaner or application can provide the conditions for a vacuum cleaner to operate at peak suction power. Motor Power and Heating Suction power can be increased effectively by using high-powered vacuum motors provided the air velocity also increases. A high-powered vacuum motor needn’t produce additional heat if the efficiency of the vacuum motor is high enough. From the law of conservation of energy, we can calculate the heat produced by the vacuum cleaner motor and measure the exhaust air temperature.

Power(in) = Power(out) + Heat

Changing the subject of the formula Heat = Power(in) - Power(out)

Let’s compare 3 vacuum motors; please download the Motor Air Performance data sheet; 1) Ametek Thru Flo 116955-00 motor nominal input power 960 W used in the Impress backpack vacuum cleaner. 2) Domel Thru Flo 440.3.403-5 motor nominal input power 1400 W now discontinued. 3) Domel Thru Flo 463.3.409-8 motor nominal input power 1450 W used in the Advantage backpack vacuum cleaner. using the most favourable point for comparison from the motor data sheets that follow i.e., peak output power and 19mm orifice, we have tabled the results below. Note; the inlet air temperature when testing was 20°C. Motor Comparison Results

Motor Type

Input Power

Output / Suction Power

Heating Power

Air Flow

Motor Efficiency

Exhaust Air Temperature

Ametek 116955-00

1062 W

329 W

733 W

24.6 l/s

31.0 %

44.7 °C

Domel 440.3.403-5

1574 W

615 W

959 W

29.8 l/s

39.1 %

46.7 °C

Domel 463.3.409-8

1336.2 W

640.8 W

695 W

30.2 l/s

48.0 %

39.1 °C

Indeed, the Domel motor 463.3.409-8 used in the Advantage backpack vacuum cleaner is exceptional, it uses the latest motor and fan design producing tremendous airflow, suction power, and high vacuuming efficiency. The high-powered, less efficient, now obsolete 440.3.403-5 Domel motor, increased the exhaust air temperature. That being the case, less efficient high-powered motors can cause overheating resulting in costly vacuuming downtime. Other factors such as motor life, weight, and cost influence the choice of motor, and in that regard, the low-speed Ametek motor used in our Impress backpack vacuum cleaner provides the longest motor life. DOWNLOAD DATASHEETS:

Domel 440.3.403-5 Domel 463.3.409-8

Ametek 119655-00