Vacuuming principle question

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.

Except then you have to remove all the air from the fat pipe too - it is a catch-22.

Bad example! It doesn't take a particularly sensitive voltmeter to distinguish a four-volt drop from 40 millivolts. 12 ga copper has about

Even with gage 0 wire, at 0.1 ohms per thousand feet, there would be a quarter-volt difference for 5A in a 500' run vs 5' run.

It's like a bucket brigade through the conductor, sort of like those swinging ball desk toys from the 1980s. The electron coming "out" of your wire isn't the same one going in. Materials that are good at doing this, like metals are great conductors. Others like glass or plastic are bad at letting current pass through them.

yup.

There's got to be some sort of "vacuum impedance" or conductance to volume matching formula out there, although I can't figure out what's it's even called.

The Lesker Company has good docs on stuff like that on their website:

It looks like "Effective Pumping Speed" is the matter at hand:

The tech support person or people there are REALLY good.

You are right - I was off a decimal point.

Yabut, so like the vacuum hose (for a while anyway)

It's just a matter of scale (Reynolds)

jsw

The ones listed there seen to be for the constant flow of gas/steam/liquid. The problem is the pressure isn't constant in a pumpdown scenario.

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." ) "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 ).

Agreed; an analogous electronic circuit would have a lot of leakage over, under, around, or through something.

My apologies to all for the distraction from the subject at hand.

Frank

An example: my 5 hp leaf vac has a 6" dia hose, 6' long. The "vacuuming suction" is very good. I thought a 12' hose would be more convenient and added another 6'. The resulting vacuuming suction was so poor as to be useless.

Bob

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-)

Conductive plastic is used as the shield for some cables. Like foil, it needs a drain wire to be able to connect it to ground.

The line to the upper floor has the advantage of gravity and the mass of the air in the pipe. You need a flow gauge to see the difference.

Not a factor.