SUCTION
(also referred to as Waterlift or Vacuum):
This
measures the suction strength of a central vacuum motor. Essentially, it
tells how much "pull" or "lift" power the motor has.
This measurement is always taken at it's maximum value at the 0" inch
orifice (sealed vacuum) where suction is at it's greatest.
Often referred to as Inches of
Waterlift or Vacuum, Suction is vital to overall system performance since it
is the "pull power" that creates the velocity of Airflow necessary
to move debris through the complex network of
vacuum pipe, hose and accessories. While Airflow is necessary for a vacuum
cleaner to work, suction creates the lift and the airflow velocity which sweeps
the dirt away.
Of any performance rating, suction is perhaps the best measurement to evaluate
and plays a crucial role in providing
and maintaining performance where it counts, at the end of your central vacuum hose.
Understanding
Suction:
Suction
(Vacuum) alone does not move dirt and debris but it is crucial for system
performance.
Consider this: Place a marble on a table,
then with the unit shut off, place your hose nozzle over the marble so that no
air can enter. Next, turn the unit on, wait a few seconds then shut the unit
off then lift the nozzle off the table. You will notice the marble hasn't moved even under tremendous vacuum!
Now
perform that same experiment but when the central vacuum is running, lift the
nozzle off the table so that air can enter. You will notice the marble whisked
away due to the rush of airflow. If not for suction power, the velocity of
airflow needed to sweep that marble away through the complex network of a
typical central vacuum system would be insufficient.
AIRFLOW
(also referred to as CFM Cubic Feet Per Minute):
This
measurement takes into account the volume of air being
displaced in a vacuum system. Airflow is usually expressed in cubic feet per
minute or CFM.
The
more Airflow/CFM a unit has the more air movement is generated thus increasing
sweeping power. This works in tandem with Suction in your central vacuum
system.
Airflow can be a bit confusing
however. Since all performance measurements are taken directly at the motor in
a laboratory setting, this does not
factor the resistance found in a typical central vacuum system. Filtration,
piping, hose and accessories used all restrict and reduce the amount of actual
Airflow a system has. While Airflow is important for cleaning and moving dirt,
Suction maintains the Airflow velocity necessary to
sweep dirt and debris away.
Understanding
Airflow:
Airflow
(CFM) is the movement of air which sweeps dirt away like dust in the wind.
However without suction the movement of air is non-existent so it is
necessary that both CFM and Suction work together.
While it is this movement of
air which carries debris to its final destination in your central vacuum,
restrictions within your system cause friction which in turn reduce Airflow.
Consider this: Take a
folded dish and cover your mouth and blow through it. Now do the same
without the towel and blow. You will notice the amount of airflow is far greater without
the towel over your mouth. The
same thing happens in your central vacuum installation which is restricted by
the friction loss through the piping, filtration, hose and tools.
Airflow "Velocity"
Velocity:
This factor is an expression of the speed at which air is moving at any given
point in the vacuum system, expressed in feet per minute (FPM). While Airflow
(CFM) will tell us the amount of air moving, a Velocity measurement tells us
how fast.
There is a
linear relationship between airflow and velocity. As one goes up, the other
goes up directly. If you know the airflow CFM and the size of the opening it
is passing through, you can then compute the velocity as follows: Formula:
Velocity (FPM) = Air Flow (CFM) divided by tube area (sq. ft.).
Understanding
Airflow Velocity:
While this is a term you will
never see published in any central vacuum brochure or specification
sheet, it is worth mentioning as a means of understanding how airflow works
to clean your home in tandem with Suction (waterlift).
What’s the difference between
the wind picking up dust and blowing it around compared to a full blown
tornado? It is the velocity of air.
The speed at which air travels
(i.e. velocity) has a direct impact on its ability to move debris. In the
case of a gentle ocean breeze versus a tornado/hurricane…this is the
difference between drying your laundry and ripping your house off its
foundation!
A household fan and a bathroom exhaust fan can produce a lot of airflow
comparable to the output of a central vacuum, but neither are capable of
generating enough Suction (waterlift) to overcome those resistances found in
a typical central vacuum system hence the velocity of Airflow (CFM) needed to
sweep dirt away depends on the power of suction.
Whether you realize it or not
air has weight and as ever so slight as it may be, it must be pulled through
the maze of central vacuum piping and ultimately through your central vacuum
system.
This is where suction comes into
play. The more suction the greater the ability to “Pull” air through any
given situation. This is why Suction (measured in waterlift) is so
important.
Without Airflow (CFM) dirt does
not move, but without Suction there is no Airflow. The
stronger the amount of Suction the greater the velocity of air trying to fill the
vacuum that is being created inside your system.
SUCTION
Versus AIRFLOW
Based on understanding Suction
and Airflow we can then agree that these two factors are interdependent and work
in tandem to actually clean your home.
The interesting thing however
is that their relationship to each other is at odds. In other words, when one
goes up and is strong the other goes down and is weak. This is called an
inverse relationship. As you can see from the graph, when suction is greatest,
CFM is lowest and vice versa.
AIRWATTS
(Suction x Airflow divided by 8.5)
There is a way to quantify and
predict where the "sweet spot" of a vacuum performance curve lies. The
computation of air watts takes into account the effects of both Airflow and
Suction values at the same orifice size.
HOWEVER...
this is perhaps the most widely used and misrepresented term used in the
vacuum industry.
Yes, it is true that Airwatts represent
a measurement of overall vacuum performance at the motor. The fault is
that this performance measurement is always taken directly at the motor and not at the end of the hose where actual vacuuming takes
place. BIG difference!
This is why this measurement is
so deceiving and is used by many marketers to show big performance specs when
in reality they are not as powerful as they lead you to believe. We know
suction is vital to create the velocity of airflow necessary to remove and
sweep away dirt.
Despite what the sales person maybe telling you, Airwatts DO NOT indicate
the true cleaning power of the unit. The only time Airwatts measure
true cleaning performance is when it is calculated at the end of the vacuum hose
(which no manufacturer does).
Understanding AIRWATTS:
Consider This: Imagine
breathing in as fast as you can. The strength of your lungs expands quickly to
create (Suction) and oxygen rushes quickly into your lungs (Airflow).
(Suction) x (Airflow)
divided by 8.5 = Airwatts.
Ok, now imagine
covering your mouth with a folded dish towel and that you are trying to breathe
in quickly. Not as easy with the towel covering your mouth is it? Your lungs are still just as strong and are capable of producing the same amount of suction, however the airflow or the rate at which you can
breathe air in is greatly restricted by the towel. This is why using Airwatts
as a means of calculating cleaning performance is false.
Airwatt ratings
used by manufactures do not calculate restrictions in your system which
instead of a dish towel, your system is restricted by 30' of hose, piping, fittings and
filtration.
Hence the
stronger the suction your unit has, the better its ability to
"pull" air through these restrictions and maintain the velocity of
air at the end of your hose.
Conclusion: To pick up
and remove dirt you must have airflow (CFM) but to create the velocity of
airflow strong enough to sweep away debris it is necessary to have suction.
The two work together.
Airwatts
presented on a sales brochure are
measured at the
motor and DO NOT not reflect the airflow restrictions found in a central
vacuum. Hence, Airwatts is not a true measurement of vacuum
performance despite what the salesperson may be telling you.
Suction
(measured in waterlift)
is vital to achieving higher performance where it counts....at the end of the
hose where you vacuum. It is the strength of suction that creates the airflow
velocity necessary to pick up and sweep debris away. As you would expect, a
unit with higher suction will out perform a unit with less suction because of
this fact.
Proof:
Performance
effect of higher suction versus higher airflow at the end of the hose:
To
demonstrate the importance of suction, Two vacuum units were
made: Each with identical motors and performance specs. One system put two
motors in series to create high suction, the other two motors in parallel to
create high airflow.
The resulting
graph demonstrates the importance of suction on performance at the end of the
hose. As you can see, the higher suction unit (red line) provided better
Airwatts at the end of the vacuum hose (The only time Airwatts are
an accurate measure of performance).
Graph:
Red
Line - End of Hose Airwatts:
Two motors in "Series" to create
a system with higher suction
Blue
Line - End of Hose Airwatts:
Two motors in parallel to create
a system with higher Airflow (CFM).
(Graph provided
by Lamb/Ametek - Leading Motor Manufacturer)
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