On Tue, 2 Apr 2013 19:12:16 +0000 (UTC), Cydrome Leader
wrote:

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

Steve

Short answer is alot.

the "pressure" available in a vacuum system is usually limited to that of
atmospheric, or 14.7-ish PSI.

That's all you have to work with, and that's only when you start pumping.

Since suction is the flow of gas in this case, you have to factor in the
volume you're trying to move, and it will increase as the pressure drops
making it harder and harder to evacuate.

1 cubic foot of air at sea level takes up 1 cubic foot.

Drop the pressure by half and now this gas takes up 2 cubic feet.

half that again and it's 4 cubic feet.

So you really have to pump out 3 cubic feet of air to drop the pressure in
a 1 foot cube to 1/4th atmospheric pressure.

The resitance of tube or pipe is a big deal at lower pressures. A shopvac
with a 2" hose seems pretty powerful out in the open, but if the pressure
is 0.1" Hg you're just going to get a gentle breeze if even across the
same hose. The same thing happens once pressure in your vacuum system
starts to drop. Everything gets harder and harder to do the more gas you
remove.

So the other short answer is you want the shortest, fattest pipes for
vacuum work, whithin reason for what you're doing.





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