Vacuuming principle question

How much does the length of a vacuum hose affect the vacuuming suction?
Steve

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The longer is the hose, the thinner, and the greater the flow, the more is the deleterious effect. It is the same as a hose offering resistance to any other kind of flow.
i
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Virtually no effect on suction - may reduce flow somewhat. My central vac pulls the same at the unit in the basement as it does on the second floor about 15 feet up, using the same 25 foot hose.
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wrote:

We have a Vacuflow 960--twin motors, with the unit capable of handling 18,000 square feet of building.
Length of the tubing most assuredly makes a difference. The vacuum cleaner is located in the shop, with tubing extended (underground) to the house--with the longest runs likely near 100'. There's an obvious difference of performance in the house as opposed to in the shop. 2" inside diameter pipe, if you have a question on size.
The rules of physics dictate that there will be losses.
Harold
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On Tue, 02 Apr 2013 05:32:10 GMT, "Harold & Susan Vordos"

What Clare is saying, I believe, is that the length of the hose makes no difference in the value of suction -- if there is no airflow through the hose. If you hook up a vacuum pump to, say, a bell jar or to a perfectly sealed vacuum-cure rig for composites, it doesn't matter how long the hose is. The vacuum will be the same.
What reduces the vacuum is the drag experienced by airflow through the hose. Longer hoses will measure the same vacuum at their ends, no matter how long the hose, if there is no flow. But if there is flow, the more there is, and the greater the inherent drag in the hose, the lower will be the measured vacuum at the end.
Rules of physics.
--
Ed Huntress

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wrote:

Pretty much what I implied, although not so eloquently. In reality, the longer the hose/pipe/conveyance medium, the lower will be the performance as you move away from the vacuum. Friction is ever present. It's the same with air lines.
The greater the volume that is being moved, the better the performance, thus the two motors on the unit we have. Smaller units all have single motors.
Harold Harold
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So... the implication is that "performance" here implies "time", much like charging a capacitor. Hooking a capacitor across a battery with voltage "V" will eventually charge the capacitor to "V"; putting a resistor in series with the capacitor won't affect the final potential across the capacitor: it will still eventually reach V. However, it may take longer... perhaps a _lot_ longer. <grin!>
Makes sense: If I have a "vacuum-formed plastic object" production line, I probably care whether it takes minutes, hours, or days for the vacuum at the mold to reach the right level. Or am I missing something?
Thanks.
Frank McKenney
--
Nearly every feature of the American system of manufacturing, from
the elements of the new textile machinery to the concept of
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On Tuesday, April 2, 2013 7:56:24 AM UTC-4, Frnak McKenney wrote:
wrote:

:
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eaner

It all depends on what you are doing- vacuuming stuff up requires a lot of air flowing quickly, you would need significantly less volume flow to quick ly evacuate a mold. But, a long hose would give a lot more space you'd have to pull air out of, so the most significant effect wouldn't be from the dr ag of the hose, but the volume in it.
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On Tue, 2 Apr 2013 06:18:13 -0700 (PDT), snipped-for-privacy@yahoo.com wrote:

flowing quickly, you would need significantly less volume flow to quickly evacuate a mold. But, a long hose would give a lot more space you'd have to pull air out of, so the most significant effect wouldn't be from the drag of the hose, but the volume in it. Which is not an issue if the vac is applied to the hose ahead of time,with a "gate valve" at the vac former - which is "standard practice" in production vac forming.
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On Tue, 02 Apr 2013 06:56:24 -0500, Frnak McKenney

Right.

The vacuum-forming rigs I've seen have to pull full vauum within seconds, or the plastic would be too far from the heating element for the thing to work. So I have some trouble relating to your example.
However, it looks like we're all saying much the same thing in different ways. The effect of hose length on any vacuum system depends on how much air you're pulling through it. If the flow rate is very low -- for example, if you're just dealing with the slow leak in a good vacuum-cure composite bag -- then hose length matters little. If you're trying to vacuum the dirt off of your kitchen floor, which requires a very high flow rate, the longer hose presents more friction to the air flow and reduces the vacuum reading you would get, if you measured it, at the terminal end of the hose.
--
Ed Huntress

>
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Measuring the vacuum at the hose nozzle on the kitchen floor may require something a bit more sophisticated than just taking a reading at the nozzle, since there needs to be a significant flow, but partial blockage, for the vacuum to lift any dirt. (the gap of the nozzle at the floor relates to how effectively the appliance pulls in dirt). With the nozzle elevated to 3" above a floor/hard surface, would create a dramatic difference in efficiency.
Something similar to a leakdown tester comparison may be helpful, indicating readings of the actual vacuum at the appliance inlet, and simultaneous reading at the nozzle on the floor with some percentage of restriction to flow.
Partial blockage of the flow generally results in the turbine motor speeding up (powered with a brushed universal motor), so that's another factor, I 'spose.
Vacuuming dirt from a horizontal screen surface would be a horse of a different flavor.
--
WB
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Sometimes when I post I feel like the "Samuel F. B. Morse" of MAD magazine fame:
"What hath got wrought?"

[...]

Eureka! ( Which is apparently Greek for "A minor crack in my otherwise impermeable wall of ignorance is dimly illuminating the back of the cave." <grin!> ) "Flow". "Rate".

Sorry. After reading the folowups I think I can clarify ( famous last word! ) the source of my confusion. I had been reading all the references to "vacuum" and interpreting them as "end-state air pressure", a static value vaguely analogous to the end-state potential across a capacitor in a DC circuit. Depending on the circuit resistance, the capacitance, and the potential feeding the circuit this can take femtoseconds or gigayears ( though the latter doesn't seem all that useful <grin!> ).

Agreed; an analogous electronic circuit would have a lot of leakage over, under, around, or through something. <grin!>
My apologies to all for the distraction from the subject at hand.
Frank
--
It's not what we don't know that gives us trouble, it's what
we know that ain't so. -- Will Rogers
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On Wed, 03 Apr 2013 17:18:04 -0500, Frnak McKenney

Well, I don't think it was a distraction. This is something that may sound simple on the surface but which benefits by looking at it from a variety of angles.
For example, I just had to use my shop vac to get the leaves out of my English ivy. That results in a lot of flow and fighting to keep the vacuum up with lots of leaves jamming everything up. d8-)
--
Ed Huntress

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On Tue, 02 Apr 2013 06:56:24 -0500, Frnak McKenney

The size of the hose matters a lot more than the length in that situation. You can use a 2 1/4" diameter hose 5 feet or 50 feet long with only a very small effect on the "performance" of your vacuum former, as long as the hose cannot shrink or collapse, but put in a restriction to 1/4", whether it is 1/8" long or 3 inches long, and you will see a huge drop in performance. Your final mould pressure will be the same, but the plastic will have a lot more time to cool down with the restriction. Even a restriction to 1 inch will make a measurable difference if the vac former is large enough.

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On 4/2/2013 12:38 AM, Ed Huntress wrote:

Same with electricity.
Vacuum = Voltage.
Length of hose = resistance.
Air mass flow = Current.
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the

http://en.wikipedia.org/wiki/Reynolds_number
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wrote:

But if the resistance per circular mil foot is relatively low, and the conductor guage(number of circular mils) is high enough, the number of feet becomes a very small part of the equation. IE, if you have a 5 amp load on a 12 ga conductor 5 feet or 500 feet in length, it's going to take a sensitive instrument to read the difference. Put 30 amps on a 22 ga wire and the difference between 5 feet and 15 will be readily discernable (if the wire lasts long enough to measure it )
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snipped-for-privacy@snyder.on.ca wrote:

electricity doesn't exactly translate to vacuum stuff, although it's more accurate than the electricity to liquid in pipes model.
there's far more gas to evacuate from a fat long pipe than a small short one.
With conductors you just add an electron on one end and another comes out the other end, you don't have to "fill" the wire first- you don't have to charge up a wire to get it going, like with a garden hose.
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On 4/2/2013 2:19 PM, Cydrome Leader wrote:

But if you don't "charge up the wire" how does the electron that goes in have a place to go in???
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You do have to charge up the capacitance between the wire and the rest of the universe. It usually isn't enough to notice except for coaxial cable, which is around 30pF per foot. http://www.microwaves101.com/encyclopedia/z0.cfm jsw
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