The role of Lift in Your TM System

    One of the better articles I posted in 2001, all the principals involved then have not changed..........

Lift determines how much CFM your wand will flow!
Posted By Ken Harris on 11/4/2001 at 3:59 AM
While I was answering a post yesterday,it occured to me that most here do not understand the relationship that your TM's air flow(CFM's) and your wands ability to translate that into a clean and dry carpet have in the real world of cleaning. I will explain this in detail to make the subject more understandable.

First lets take a typical set-up as a good example of a real world situation. The 4M blower is probably the most common one out there so we will examine its air flow characteristics. This blower will usually put out about 320 cfm @ 14" HG(a typical setting) when turned at the usual 3000 rpm. This would be measured at the blower outlet. By the time system losses in the vacuum tank are deducted that number will be reduced to about 300 cfm or so. Add another 100 ft of 2" hose with a 1.5"- 10 ft whip hose and that flow is down to about 250 cfm. Still sounds pretty good,but what happens when a wand is added and the lips of that wand are put down on damp plush carpet. Your airflow is cut in half! The wand/carpet interface is such an obstacle to air flow that nothing else in the airflow system comes close. What you can do about it is what the rest of this article is about. After all, 125 cfm doesn't sound too impressive when you started off with 320, does it?

The role of Lift

What is lift in the context of carpet cleaning anyway? Well look at it this way; we all rely on the 30" HG of air pressure that surrounds us to force the air,water and soil into our wands when they are on the carpet cleaning. This is accomplished by dropping the pressure in the wand and hose to a low enough level that the higher air pressure outside the wand will cause air to move inside it. The greater the differential in those pressures the greater the lift that system has. As a simple example of this lets say that your system operates with the vacuum at 10"Hg. This means that the pressure inside the wand at the lips is really at 20"HG(30"HG- 20"HG= 10"HG)The guage is really measuring the amount of pressure drop from the normal outside pressure(30"HG). Air always flows from high to low pressure and the greater that difference is the faster and more that volume(CFM) of air movement that will be.When the wand is on the carpet cleaning the Wand/Carpet interface is a very hard blockage to get by so maybe only 125 cfm from your original 250 cfm available to go into the wand can make it thru there. If the lift of the system is increased to 15"HG instead of 10"HGwhat do you think will happen? Now there is 15"HG difference between the air pressure inside the wand and the air pressure outside. More air will now push past the wand carpet interface and in doing so the volume of the air(CFM) will increase too.The cfm may be up to 150 now which will increase your ability to clean that carpet better(especially heavily soiled ones),and the increase in usable cfm's will definately dry that carpet better.By getting your system to operate at 15"HG you have improved your real cfm flow capability by 20%(150cfm/125 cfm).

This is why all 4M blowers are not created equal! Some will operate at higher levels of lift than others. The 4MP blower will operate at 16"HG all day long and allow you to run long hose runs when you need to while delivering excellant cleaning results because of its higher "real" cfm capability. A Roots 47 blower run at its normal lift setting of 12"HG wont be as effective at letting those extra CFM's thru your wand. Bottom line here is this: The vacuum system that can create the greatest lift numbers at the wand/carpet interface is really the one that will move the greatest amount of air(CFM)into your vacuum system and dry the carpet the fastest; all other factors being equal.

Thanks,

Ken Harris
Turboteck Supplies

A #4blower you say = 300cfm's.   Well blow me down, I should have bought another Recoil which states in the ad it has 300cfm's instead of my TM......lol

Not comparing apples to apples when you do that John. Portable machines advertise their CFM production in a different way than Positive Displacement blowers do.A blower can deliver most(over 90%)of it's cfm against RESISTANCE. This means that it can deliver 300 cfms even at 15"HG lift showing at the truck. The 300 cfm figure that is advertised with the Recoil or any other machine that has 3 vacuum motors is derived by simplely adding up the maximum that each motor is capable of delivering(100 cfm)when operated with NO RESISTANCE. Thus 100 cfm X 3 =300 cfm. But a centrifugal vacuum operated at 90% of its maximum resistance(such as cleaning a carpet)loses 80 to 85% of its cfm output because of a thing called SLIP. This means you only get 15 to 20 cfm from each motor once the resistance of each one in parallel reachs 100"WL. Thus the portable is only good for 45 to 60 cfm under use conditions.One that I tested in California tested at 49 cfm so this works pretty close to that.

Now you know why most people buy TMS. The positive blowers are much more powerful under use conditions. Does this mean someone gave you mis-leading info? No, it just means that you did not make sure you looked deep enough for the facts before reaching your wrong conclusion is all.
    

Edited by Superglide Ken - 11/November/2006 at 6:34pm

Thanks Steamer. I agree. Only a maximum of one extra technical post a day so readers can keep up. I hope that is not too fast?

All blowers are positive displacement, Doug. If you are referring to Cleancos when you say colds, then you should know that the standard blower in them is a Roots 45. That blower is rated at 320 cfm at 3000 rpm, but Cleancos do not spin them that fast. They use a pulley system that multiples the engine speed by 1.5 X to reach the blower speed. So the 1600 rpms that they get set for gives you a blower turning at only 2400 rpm.

This is what happens to cfm:

320 cfm X 2400rpm/3000 rpm = 256 cfm

This also reduces the heat output as well, thus earning the name Cleancold. Most cannot get to 200 degrees at the truck that I have seen unless it is a Summer day.

I fixed that problem. If you adjust the set rpm up to 1900 rpm setpoint, they will go up to about 220 degrees on a 20 degree day. They are not Cleancolds anymore.

This is what happens to cfms:

320 cfm X 2850 rpm/3000 rpm = 304 cfm

The extra 50 cfms you get will dry carpet at least 1 hour faster than before. The cost? Maybe $1/hr more for gas. If you are under Cleanco's warrantee, don't make this adjustment yourself though.Kleen Kuip knows how to do this, and they can tell you if your warrantee is effected if you do. If you are off warrantee like I am, then you do not have much to lose, and lots of performance to gain IMO.
    

Edited by Superglide Ken - 11/November/2006 at 8:50pm

doug wrote: To bad clean colds don't come with a positive dissplacement blower? I think cmaster has changed a few since I came here? The only positive thing is they don't last?

Sucking up squirels?

3000 rpm is toooo fast...kills the engine