DIYbanter - View Single Post

Cydrome Leader

wrote:
On Tue, 02 Apr 2013 07:37:34 -0500, Richard
wrote:

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

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.

Same with electricity.

Vacuum = Voltage.

Length of hose = resistance.

Air mass flow = Current.

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 )

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.