Tri lobe or dual lobe Blower Larry ? The charts state the opposite of what you are saying.
CFM goes up, lift goes down
CFM goes down, lift goes up
I guess it depends on what blower you are testing
I would like to comment on this as well - you are
both right because you are talking about
two different things!
Todd's comment is correct, but remember - the charts refer to a bare blower, not a complete system.
The blower moves the most air if the inlet and outlet are completely unrestricted - so low vac equals high(est) cfm. As you restrict the inlet naturally the cfm decreases and vac rises, so high vac equals lower cfm (but not a
bunch lower, just a little). The charts simply indicate the obvious - as you increase the blower inlet restriction you will create vacuum and in the process move a little less air.
Larry is referring to a complete system, a TM.
If you start a TM and hook up a hose and wand (and maybe put the wand on carpet) you are restricting the blower inlet. Same as above? Nope - your TM
system has a vac relief! When Larry talks about raising the vac it's done by adjusting the relief to a higher setting,
not by changing the restriction at the blower inlet, so the chart no longer applies.
Think this through in your mind - I'm just making these nice round numbers up but you will get the point. Lets say at 13" the wand is flowing 200cfm and the relief valve is flowing 200cfm (you have a 400 cfm blower). You crank up the relief setting to 16" so it closes down to raise the vac, and now flows only 100 cfm. The blower speed hasn't changed and it's a positive displacement pump so it
still wants to move 400 cfm - and the air has to come from somewhere - so more air flows through the hose/wand (OK Todd you're right - according to the chart at the higher vac it's only pulling, say, 380, not 400, but the hose still has to flow more air - 280 vs 200 - to make up for the reduced relief flow). Thus Larry's correct comment that increased vac
at the hose connection moves more air through it and the wand.
Another way of looking at it is to remember what
actually moves the air - it is atmospheric pressure that
pushes the air into the hose. Why doesn't air flow through a bare piece of hose that has both ends open? Because the atmosphere is pushing just as hard at both ends. Think of you and your buddy trying to move a car - you are pushing forward from the trunk and he is pushing backwards from the hood. Obviously the car goes nowhere. I (the blower) grab your buddy (atmospheric pressure inside the waste tank) and yank him out of the way. Now you (atmospheric pressure at the wand) are now free to push the car (air inside the hose) forward (toward the waste tank).
The more air the blower can yank out of the way the easier it is for atmospheric pressure at the wand to push air into the hose. Said another way, the higher the vac at the hose connection the more cfm flows through the hose!
That's all I got - going to bed...
