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Central vacuum terms and definitions
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Presented in alphabetical order, except for a couple of very important ones at the beginning.

VACUUM (Water Lift)
Inches of water lift. (Usually given at 0" air opening).
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 fluctuate 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 given 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.
AIR FLOW CALCULATION: 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)
Note: Both the CFM and the waterlift must be at the same air opening size

AMPS 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 specifications.

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. Read our vacuumology article.

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

OVERALL EFFICIENCY "Measure of Fan Efficiency"

          AIR WATTS 
        INPUT WATTS 

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 expensive.

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.

See Vacuum (first definition).
Central vacuum terms and definitions

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