Blower CFM ratings

FastEddie

Member
Joined
Oct 19, 2006
Messages
435
Readings Taf's article posted on my 2" hose to the wand, more CFM's or Lift? thread:

http://www.cleanfax.com/article.asp?indexid=6632732

I noticed that blower ratings are calculated with no hoses attached, how lame. While a #45 blower is rated at 320cfm, what is the actual decrease in ratings in the real cleaning world when you add 100-150 ft of hoses?

So I guess most blowers under a 56 are not taking advantage of a 2" hoses max rate of 500cfm rate?
 
G

Guest

Guest
Eddie: It depends on the actual volume of air(cfm) that you are trying to move thru the hose. Higher cfms cause the cfm reduction to be greater as you approach the limit of the hoses flow capacity(500 on a 2",near 700 on a 2.5"). In the real world where most are limited to 150 cfm or so at the wands WCI, this does not really matter much however.

In that case, you are much better concentrating how much lift you have at the wand. This is a very easy thing to do, as lift is reduced at a constant rate as you move away from the vacuum tank. Lift(measured in " of Waterlift) reduces by an average of 1/4" per ft of 2" hose. That works out to 25"WL per 100 ft of hose.

Say you have 200 ft of hose hooked up. That would mean you would see a reducion of 50"WL. If you had 207"(15"HG) back at the TM, you would now be down to about 157"WL(11"HG) out at the wand. That is a reduction of about 24%. Since cfm is a linear relationship to lift, you could say that cfm will be reduced in the same amount, at least when the wand is not on the floor, bringing the WCI restriction into effect.

320 cfm X 76% = 243 cfm

But the cfm flow will rarely exceed 50% of the potential cfm flow when it goes by the WCI, so I would say you are looking at no more than 120 cfm even with a glide on your wand at this distance.Those that have less than 15"HG showing at the truck will of course have even less than this figure.
 

FastEddie

Member
Joined
Oct 19, 2006
Messages
435
Comparing a 59 blower to a 47 sucking thru 150ft of hose thru a hole glided Ti wand with lift set at 16hg. With the glide on the carpet and working, is there gonna be a difference?

This shit makes my brain bleed.
 
G

Guest

Guest
Single wand, not much. Dual wand.......huge difference. BTW, both those blowers are long lobe blowers and neither one is designed to operate at 16"HG. 14"HG should be the max lift setting on either one. If you want a little more lift(15"HG),but still huge cfm capability(600 cfm), use a 56 blower. It is a stronger design than the other 2 you mentioned. The 68 blower is great as well if you have the torque to power it.
 

Frank P.

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Joined
Oct 28, 2006
Messages
66
Lift

Ken by what you are saying a portable such as the Eclipse with 249 in. lift & 17.8 Hg minus 6.25 in. at 25 ft would be far better than most TM's at 200 ft of hose on a live reel. What is the drop in CFM or lift in a 1.5 in. hose?

Frank P.
 
G

Guest

Guest
Frank: Two things you need to understand . First, positive displacement blowers as used on TMs calculate their lift values in a different way than centrifugal vacuum motors as used in portables do. TMs are still moving lots of air(cfm) at their rated maximum lift values.Portables list the maximum lift with NO air moving.What this means is even if a smaller blower like a #36 is at 15"HG(207"WL), it will still move at least 250 cfm of air thru the hose attached to it. If you hook up 3 vacuum motors in series and apply restistance to them by adding a hose and wand, the 100 cfm potential of those motors will be reduced to a much smaller 30 to 35 cfms. This is because the centrifugal vacuums have much more slip than a positive displacement blower has. Second, since water is carried in the airflow, the positive displacement blower will move usually 5 X the airflow under working conditions than a vacuum system operated in series, so it will dry much faster. This is why guys with TMs can operate the pressure and flow at much higher levels than portable guys can even though the lift of both machines sounds simuliar by the numbers published in the specs on paper. They are not in reality. BTW, lift reduces by 1/4" per foot in 1.5" hose as well when less than 100cfms goes through it, which is the case with nearly all portable machines.
 

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