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.