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I have 1600 Watt vacuum cleaner, I need to use 32 ft of hose (10 meters), I have a choice here, whether I buy a hose with diameter 3 inches (75 mm) or 2 inch (50 mm) or 1 inch (25 mm).

Which hose diameter will provide less resistance, better airflow i.e. will allow my vacuum to work more efficiently?

Could you also explain in layman terms in terms (without formulas) about physics why diameter play big role?

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  • $\begingroup$ May need to increase fan power. $\endgroup$
    – Solar Mike
    Sep 3, 2022 at 20:47

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You need a certain air speed in the hose to transport the material without it separating. The easiest way is straight up - there is no tendency to dump the solids. The hardest way is at a modest slant. You need the most power per unit of stuff. Bends and kinks can help keep the stuff entrained. So try big, and if the solids fall out, you need to go smaller and faster.

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Suppose air flow constant. The bigger pipe diameter, the less will be linear air speed. There is friction between air and walls and between air layers too. The closer a point to pipe wall, the lower linear air speed due to friction. Very roughly we can assume zero air speed at the border between air and pipe wall. Thus, bigger pipe diameter gives lower air speed that gives lower friction and lower pressure drop along pipe.

Another factor. Intake pressure is atmospheric. Than the bigger pressure drop along pipe, the lower pressure in the VC fan. Lowering pressure causes lowering of its efficiency. These two factors yields in nearly exponential airflow decrease at pipe resistance increase.

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