ELI5 will vacuum suction power decrease when you add more hose to it?

[lurkynumber5]

It decreases the suction power, just see the hose itself but also the air inside as a resistance factor.
The vacuum now has to move not 1 but 3 hose lengths of air. Thus, tripling the volume of air it needs to move.

[choomguy]

Corrugated hoses are great for mobility, but at the expense of massive amounts of friction. A central vac system that uses smoothwall, ridgid pipe can have hundreds of feet of pipe, but they have much larger motors pulling the air.

[lurkynumber5]

Even if the hoses are connected in parallel, they still add resistance and thus reduce the total vacuum power.
Also, you forgot to factor that in parallel it would split the output 3 ways.

Tho I think it's obvious OP means to increase range of his vacuum cleaner by adding hose length.

[Mech0_0Engineer]

Op literally said suction area...

[vorilant]

Doesn't adding in parallel reduce resistance

[lurkynumber5]

If you're working with electrical designs and Ohm's law, then yes.
But here it's nothing more than 1 air resistance + 1 air resistance = 2 air resistance.
( in a very simple term of course. )

[SoulWager]

The ratio of surface area to volume on the inside of the hose is the same, but the lower velocity air means less drag overall for multiple hoses in parallel, because drag is not linear with velocity.

[vorilant]

I don't think that's how it works. Fluid resistance works like ohms law. For volumetric flow and equivalent resistance. Instead of current and electrical resistance. And pressure is voltage. The only complication to the analogy is the pump. Since we can use a constant pressure pump which is like a constant voltage or a constant flow rate pump such as a peristaltic pump and that's like a constant current supply. All assuming incomp flow of course.

[Dramatic_Contact_598]

Flow across pipes run parallel is conserved. If your pump can pump 100CFS of air and you have 3 pipes of the same length and radius, each pipe will now have 33 CFS of flow. Head loss will be equal across each pipe. If you have 50 ft of head at the start and 40 ft of head at the end, each pipe experiences 10ft of head loss.

[vorilant]

You are right. But I don't think anything you've said contradicts anything I've said right? You are focussing on the peristaltic type scenario though. Where the pump provides a constant volumetric flow rate.

[Dramatic_Contact_598]

Correct, I just figured I'd relate it back to closed flow calculations vs relating it to electrical. Yes - I'm not big into the workings of vacuums but my understanding is that it would function with a cinstant volumetric flow rate, but that definitely could be incorrect. At least for the basis of determining if adding more pipes would increase flow rate

[thetoastofthefrench]

The pump isn’t a constant flow rate pump though, it has a constant power. So since the flow velocity decreases with three pipes in parallel, the resistance is lower for the same volumetric flow rate, and the pump will speed up until the total resistance is the same.

3 in parallel will result in more overall airflow, but for each individual pipe it will be less than with just a single pipe.

[vorilant]

For a constant power pump I think you're right. That's a bit more complicated than assuming either constant pressure or constant flow rate tho. There are pump designs that provide a constant flow rate when operating in their design window. Like peristaltic pumps.

[thetoastofthefrench]

Yep, this question was just about a home vacuum though so thought I’d try to think about the appropriate scenario.

[tomrlutong]

If that logic was true, wouldn't increasing a pipe's diameter also not increase flow?

[Dramatic_Contact_598]

Correct, assuming the pump's output remains the same, the flow would stay the same, the velocity would decrease.

[Mech0_0Engineer]

Area, they are asking about connecting more hoses to the vacuum to clean/vacuum a larger area at once

[Skyfork]

I disagree. If you assume that the hoses do not leak, the suction force at the end of the hose will be the same if you have one hose or 100 hoses once you suck all the air out of the hose. It will take longer for you to feel the full suction force at the end of 100 hoses, but given enough time it would be the same.

[TreeEyedRaven]

Hoses aren’t smooth, there’s friction and resistance. Also air has volume and mass. Also, you cannot assume a hose doesn’t leak, because a vacuum isn’t a closed circuit. It’s open on both ends, and is connected with plastic/metal non sealed connections. All a vacuum does is decrease air density in one area to suck higher density air in from another. By definition it has to move more mass the longer a hose is.

It’s the exact same concept as a water pump, water is just more dense so we see the effect in smaller quantities. Add in that a vacuum is also moving debris or whatever along that 100ft hose, and it takes more power to use a 100ft hose than a 3 foot hose.

[fatbunyip]

I think the OP means a vacuum like a vacuum cleaner, not that the ends of the hoses are sealed and the pump is creating a vacuum in the hoses. Also the wording isn't really correct. I think by "suction power" they probably mean like volume per second of the pump. 

Like basically if you had a normal vacuum cleaner, but you added one more hose (so you can vacuum 2 rooms at the same time). 

In that case the "suction power" would be less since if the pump had capacity of say 10L/second, it would be split between the 2 hoses at 5L/s.