Does anybody have experience using a DC as a central vac?
I have central vac for my house and the vacuum unit is old and
needing replacement. I also need a DC for my shop. I was thinking
about using a DC for both applications, but I don't know if
the 2 applications have the same requirements. I know that a vac
or a DC have 2 properties: inches of vacuum at no flow, and cfm
at no vacuum.
Has anybody tried this, or what do you DC experts think?
I don't think that it will do what you want it to. A DC just doesn't have
the static pressure to work well as a central vac just like a central vac
doesn't move enough air to work well as a dust collector.
If at first you don't succeed, you're not cut out for skydiving
"Rex_flex" < firstname.lastname@example.org> wrote in message
Someone asked this at a Penn State bulletin board a while ago. The reply
was that you will end up burning the DC out because it can't handle a
restricted load like that. They said if you can only afford one, to get a
Fein vacuum; it isn't good as a DC, but at least it will work.
I agree that a DC won't make a good vacuum, but I'm pretty sure that burning
it out on restricted load is a myth. A DC is a centrifugal device, not a
positive displacement device. As you restrict the airflow, the motor load
goes down. To the limit, cutting off the airflow completely puts that motor
at a virtual idle state. This can be confirmed by looking the motor
horsepower requirements in the blower curves.
I just read an article that may be a better explanation of why a dust
collector could burn out trying to use it as a vacuum. The dust collector
service, unlike most power tools, represents a heavy start load. Compare
the sound of a starting table saw to a starting dust collector. The saw is
at full speed almost instantly. The dust collector ramps up to speed, due to
the heavy impeller. This represents a heavy starting current for the motor,
which can cause a heat buildup. For that reason, dust collectors should not
be stopped and started frequently. A central vacuum service might represent
more frequent starts than dust collection service.
Air flow through the motor is not restricted (with proper design) when
the dust collection airflow is throttled. Motor cooling air flow
results from the motor's internal fan, not the collector impeller.
And the motor speed doesn't slow down when the collector system
airflow is restricted/throttled - the motor speed actually increases
slightly with reduced load.
Bob (with his second post) hit the reasoning for a statement that
"dust collectors will 'burn out' if used like a vacuum" - it's the
frequent starting. Motors don't like starting loads. The increased
starting current causes heating. Too many starts in a short period
will heat to the point of insulation degradation. NEMA (Nat'l. Elect.
Mfgrs. Assoc.) has standards for number of starts per hour that motors
should withstand. Solid-state devices are available to decrease the
starting current (soft-start) if you want to start/stop your blower
Hope this helps,
Motors used in dust collectors and most power tools run at constant speed
from zero to rated load. I don't know what you mean by a restricted motor.
It will be moving the same amount of cooling air whether its loaded or not.
The motor only sees the load through the shaft. If there's no load on the
equipment, then there's no load on the motor, other than slinging the weight
of the impeller around.
Thank you to all the folks who posted thoughts on this matter.
FWIW, I think I have it (partially) figured out.
A DC won't make a decent central vac. This is because a DC uses
an impeller-type thing to move the air, and the impeller moves
a lot of air when there is little or no resistance, but gets choked
off pretty easily. So the DC develops a max static pressure of roughly
10 inches of water (or about .03 atmospheres). A vacuum cleaner uses
a turbine. The better ones use a 2, 3 or 4 stage turbine. A top of
the line vac moves maybe 100cfm, but the static pressure developed
is roughly 100 inches of water, i.e. maybe 0.3 atmospheres. Sucking
away on your carpet, you're moving very little air, but the only way to move
any air at all is to have as much static pressure as possible.
Thanks again to the posters.
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