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5/29/07
Some vacuum cleaners suck in more ways than one.
I'll start with the shop-style vacs. Many claim to be 3, 4, 5 or even more horsepower. The truth is, if it runs on a regular wall outlet, it's about 1-3/4 horsepower maximum. That's simply all the power that is available from a wall outlet. See my article about air compressors for more on this.

At one time, these vacs were sort of rugged creatures. But most of what I see today look like a big plastic kid's toy of some sort. And some of them appear to devote a good portion of that horsepower to making noise! Might have something to do with the crude plastic unbalanced blower wheels in these things, that spin at 10,000 rpm or so. A good quality vacuum cleaner has a balanced aluminum blower wheel..

Now I want to point out a major difference between 2 types of vacuum cleaner guts.

Most tank or canister type, and some upright vacs use an airflow design where the dirt gets trapped in the bag BEFORE the air goes through the fan or blower. The bag on these vacs fits inside a sturdy compartment on the unit. This is a far more reliable system, as a nail or a penny getting vacuumed up simply ends up in the bag, no damage done.

But many upright vacs, as well as some small portable hand-helds, run the dirt through the fan first, which spins at about 10,000 rpm's, and then into the bag. This style usually has a cloth or 'soft' outer bag. While normal household dust going through the fan won't damage it, picking up just one nail or coin will likely cause the unit to be sitting out for trash collection next week! Before you buy one, check to see if it has some sort of protection against this happening. Most don't, even if some old fodge is selling it. And the big warranty on the "housing" doesn't include the fan or motor.

We bought one of the 'lightweight hotel' vacs you hear so much about. The belt that drives the beater brush is so thick, and stretched so tight, that as soon as you start the vac, you can smell the rubber burning just from it's own friction. As expected, the belt breaks every other time you use the thing. I decided to quit using it, before it catches on fire!

Also, when they claim so many 'amps' or 'watts' of cleaning power, they're not really telling you much. An inefficient motor or poorly designed blower can result in a higher amp or watt rating, but not more cleaning power. If the machine looks like a kid's toy and costs about as much as a kid's toy, that's probably what it is. But even some of the very expensive ones are a pile of junk too. I have an older Electrolux upright that's pretty decent.

Let's clear up one more myth about vacuums. When you block off the suction, the motor speeds up in the machine. Most people think the motor is working harder then. Just the opposite is true. The 'fan' in a vacuum cleaner is technically called a "centrifugal blower". The blades on the blower wheel "grab" a chunk of air, then spin it around in a circle at high speed. Centrifugal force then causes the air to fly outward, away from center and towards the outer edge of the blower wheel. The suction is created by new air entering the inner part of the blower wheel to replace the air that was thrown outward. When the machine is running normally, this process happens continuously. The "new" air entering the blower wheel is not spinning until the blades grab it. It takes energy from the motor to get this new air spinning, which slows the motor down. But when you don't allow new air to enter the blower, such as blocking the hose, any air that remains in the blower wheel simply spins around continuously, and the motor is not working hard to get new air spinning, so it speeds up.

But running the vacuum with the hose blocked can still damage the machine. Many vacuums depend on that air moving through the blower to cool the motor, so the motor could overheat. Also, when the same air is allowed to spin continuously inside the blower, the air gets quite warm from friction. This could cause a 'meltdown' of plastic blower parts.

As long as we're talking about "centrifugal" blowers, the one in your furnace is that type too. If your furnace filters become plugged, less air will move through the furnace. Although this can drastically cut the efficiency of the system, the blower itself will actually use less power, due to the principals explained above. The same goes for centrifugal pumps, like a sump-pump or a well pump. The
more the flow is restricted, the less power it will use, and the less water it will pump.


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