We Install Why Go Central Vac What Does It All Mean
This explains the secret of the bowling ball trick. Direct all of a vacuum's power onto one surface
area and you can do amazing things. You have seen the commercials, right?

A vacuum's ability to lift is a valid measurement. In fact, it is called vacuum, or water lift. See how
strong a vacuum can be by simply swallowing the air out of a two liter plastic soda bottle. That is
actually about all it takes to lift a bowling ball!

The suction capacity of a vacuum is not the key to effective vacuuming. The real key is how much air
the vacuum moves and how fast it moves it (see CFM below). Water lift becomes somewhat
important when the air opening size is smaller - for example in air driven brushes, because the
strength of the suction keeps the air turbine spinning when tension increases.

Water lift measurements will fluxuate based on the actual amount of voltage the motor is receiving,
the altitude, air temperature, and the barometric pressure.

CFM (Air Flow)
Cubic Feet (of air) per Minute. (Usually give at 2" air opening).

Wonder why that pebble won't vacuum up but stays rattling in the end of your vacuum wand?
Basically, without sufficient air moving around it, it's going no where. Even a feather won't budge
without any air moving past it. Therefore, CFM (air flow) is crucial for deep carpet cleaning. Some
vacuums may be able to lift bowling balls, but the cleanest homes have central vacuums with tons
of CFM. CFM becomes more important as the air opening size gets larger. You can feel the air
rushing in to a straw when you inhale, but you wouldn't feel a thing if you put your mouth around a
two inch pipe and inhale.

CFM = 13.35 d² (square root) VAC in H 2 O" Need:  d - Diameter of orifice plate  
vac - Inches of water lift  

* Vacuum must be corrected before being put into equation. To correct - temperature and
barometric pressure must be accounted for.


The air around us constantly exerts a pressure of about 400 inches of water. That means that every
exposed surface has the equivalent of 400 inches of water pushing on the surface. A vacuum
cleaner doesn't actually create a vacuum, but it does lower air pressure inside the vacuum unit.
Since the outside air is at normal pressure it rushes inward in a controlled airflow which creates
the cleaning effect.

"Cleanability Rating"
CFM x VACUUM (Water Lift)  8.5  
Note: Both the CFM and the Waterlift must be measured at the same air opening size.  

Current draw of the motor.
Amperage current draw of electricity required to operate the vacuum motor. A motor that uses more
electrical current does not always mean the current is being used more efficiently.

The center part of the motor which rotates making the transfer of electricity across the motor,
enabling the motor shaft to spin. A quality armature is mounted on ball bearings, and protected
from incoming vacuum air that has been heated and dirtied.

A separate stream of air that cools the motor, different from the air that draws in dirt from the home.
Air being vacuumed does not actually flow through the electrical components of the motor.
Normally these motors have a separate fan to provide cooling air to the motor.

Cyclonic action describes the natural action found in a tornado. In a vacuum with cyclonic filtration,
the air carrying the dust and debris moves through a tornado action. The air swirls downward in a
cone-shaped pattern. At the bottom of the cone, it starts swirling upward again, inside the
downward cone. Thus this is sometimes called a "reverse" tornado action or "dual cyclonic action".
The vast majority of the debris separates from the air stream as air reaches the bottom of the swirl,
and is deposited in the dirt container. A fraction of the debris remains in the air, to be removed by
the secondary filter, if there exists any secondary filters.

FAN (and fan stages)
The fan is the combination of blades that spin around to create the airflow to produce the
vacuuming action. Fans are flat impellors, and are combined in a set of two or three fans on each
motor, depending on the model. A motor with two fans is called "two-stage"; if it has three fans it's
"three-stage". Each fan - set of blades - increases the sealed vacuum, or maximum air pressure
drawn through the system. Additional sets of fans will change the air flow dynamics, adding fans
will increase waterlift and decrease CFM. Air driven power brushes work better with a motor with
more fan stages, whereas electric brushes operate better with less fan stages.

HEPA stands for High Efficiency Particle Arrestor, used to reduce the number of contaminants in
indoor air. A HEPA filter will arrest or stop 99.97% of all particles .3 microns or larger. HEPA filters -
used in "clean rooms" - are essential in medicine and in the manufacture of computer
components. However, they have limitations in vacuums. They tend to leak in vacuums, because
they were never intended to be used as small, portable filters. They are expensive and must be
discarded because they cannot be cleaned. They clog quickly and strangle airflow. And even when
working perfectly, up to half the respirable particles in indoor air are small enough to go right
through a HEPA filter. Very, very few vacuums are truly "HEPA" certified but many only use filter
material which is "HEPA" level. M.D. offers bags for their systems that meet this filter material

a) Peak Horsepower (PHP): Maximum instantaneous horsepower capabilities of a motor (most
frequently used but very deceptive).
b) Input HP: Maximum watts divided by 746.
c) Operating HP: Watts at operating point divided by 746.

This is recognized by the American Society of Testing and Materials (ASTM) as the best way to
measure the actual cleaning power of a vacuum system. Most manufactures provide statistics for
the maximum air watts that may not be the actual amount produced under the conditions most
often used. Make sure you know the opening size of the attachment most often used and then find
the vacuum's air watts at that exact opening size.

Measured in revolutions per minute (RPM). Higher RPM motors may not last as long.

"Measure of Fan Efficiency"

ORIFICE (Air Opening)
Simulation of restrictions (impedance) in a cleaner system.

Restriction typical of operating conditions.

A collection device for dust and debris used by some vacuum cleaner manufacturers. Paper bags
are a definitely the cleaner home owner's choice.

These are designed to loosen stubborn dirt in carpets, and make it available for removal by the air
flow. M.D. power nozzles are optimally designed to remove both common kinds of carpet dirt; our
dual soft bristles gently free debris that naturally sticks to carpet surfaces; threads, lint, pet hairs,
etc. And our beater brush agitates and vibrates carpet, to loosen the sand-like grit down between
carpet fibers.

PVC (Poly Vinyl Chloride)
A common plastic polymer that provides excellent appearance and longevity with good flame
retardance at an attainable price. All of M.D. Manufacturing central vacuum fittings - renowned for
their quality in the vacuum industry - are made from PVC.

Hose, wands, filters, carpet, water, foam, voltage fluctuation (anything which impedes airflow)

Often used in high quality motors to prevent dust and debris from entering the motor bearing area.
All M.D. motors have sealed bearings.

A device to measure maximum vacuum or water lift by sealing off the vacuum intake port. It
measures in "Inches of Waterlift". This is not for picking up water but a means of comparing lifting
abilities of a solid column of water.

An electronic means of slowly starting vacuum motors to reduce initial in-rush voltage spikes. It
starts the motor at a slower voltage, slowly ramping up to operation voltage. No tests by Ametek or
any other agency have ever produced any quantifiable measurement of this extending any motor's
life. It does however; allow the manufacturer to utilize a smaller capacity of relay which is less

120 volts, 60 Hz., corrected to standard conditions of 29.92 barometric pressure and 68º F.

See Fan Stages.

In some less-expensive motors, the air drawn from the home flows right through the motor to cool
it. Unfortunately this air is laden with the dust from the home which dirties and contaminates the
motor. This air is also warmed by friction as it moves through hoses and piping, and is
substantially warmer so it is less able to cool the motor. Thru-flow motors will overheat if they are
run for long periods of time without adequate air flowing through the system.

A measure of the electrical potential employed by a vacuum motor. Typically, motors require
common household current; 110-120 volts in North America; 240 volts in other parts of the world.
Voltage is to electricity as pressure is to water, a measure of potential or driving force.

Electrical power consumption of the motor.
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