Cfm and waterlift.......................

    Re: cfm and water lift?
Posted By Ken Harris on 11/23/2001 at 3:25 PM
Hi James: In capet cleaning you need both of these ingredients for effective cleaning . The cfm number is the volume of air that your vac system will produce . This number can be quoted without system loss(most are)factored in(like 300 cfm), or more realistically the net amount of air that can be drawn into the wand at the most restrictive point(WCI- Wand/Carpet Interface)can be quoted. A vac system is only as strong as its weakest link and this is it.

Most people don't have the means to measure what is happening at the WCI ,so you won't hear this as a big topic of conversation even amoung carpet cleaners. If you want the most cfms of air to go into the WCI, then you need to look at the lift that your system generates.

Lift is simply the degree of pressure reduction that can be acheived within a vacuum system, and ultimately the wand head at the WCI. For example , the air pressure all around us is exerting a pressure near sea level of about 30 HG . In a strong TM system the pressure in the tank may be only 16"HG. The gauge on your TM will read this as 14"HG because it measures the reduction in pressure from atmospheric, not what you have left(30"Hg - 16"HG= 14"HG on gauge). Generally speaking the greater the pressure reduction that your system can acheive, the greater the cfm can enter the WCI of your cleaning wand. The greater the pressure differential there between the "high" outside pressure and the much"lower pressure in the wand, the greater amount of air that will overcome the resistance at the point and will flow in. The more cfms that are drawn in here, the more water and disolved soils are taken out of the carpet,resulting in better cleaning and faster drying.

There is a limit to what lift can be created here of course. Increased lift in the system requires more hp and generates more heat. In addition most blowers are not designed to operate over 15" HG without exceeding manufacturers limits.The 4HP blower will go a little higher to 17"HG if run with synthetic lubricant.If you take them higher than this oil seals could be damaged. To maintain a safty margin most manufacturers do not recomment a setting higher than 14"HG at the vac tank. Allowing for 2"Hg loss in lift on a 100 ft hose,and the reduction from the air movement(leakage) at the WCI, you let have a lift of about 10"HG in the wand head.This with allow (depending on wand design)about 120 to 150 cfm of "net" airflow into your system under operating conditions with the wand working on damp plush carpet. This will be a very efficient system capable of doing great cleaning and about 3 hours dry time with the proper wand technique. There are ways to shorten this down even further through wand modification but thats anougher story for another time.


Thanks,

Ken