I've been experimenting with different shapes of impellers
for blowers, and I'm pretty sure an impeller
with these backwards curved fins, like this one,
are more efficient. And, coincidentally I found
another dishwasher in the garbage,
and here's the pump from that, and the impeller,
and it's very much got backwards curved fins in it,
much like this one, although this one's a little bit conical.
So, now Te question is, "Is this shape of housing
the most efficient?" This one here is also, kind of,
spiral shaped, so that gives me some confidence.
The first question in, "How do I cut the airstream here?"
I've always been leaving a little bit of space, because
the closer I get to the fins here,
the louder this blower becomes.
But, I figure if I cut the air very close to the impeller,
I should force more of it to come out here,
which would create more air flow.
If I cut it in a non-straight manner,
then it's not quite as loud,
so let's do some experiments.
I made a holder for this anemometer so I can hold it
at a consistent position from the inlet,
just to get a relative measure of air flow.
So, we're using 146 watts,
and we got about
11 meters per second right there.
And, you can hear it getting louder right away.
And then the air flow
has not gone up, power's about the same.
So, there appears to be no benefit in cutting the air flow,
it just makes it louder. But, I don't get more air flow
going through the blower, and the power consumption
doesn't go down. Next I'll measure
if cutting the air stream changes static pressure.
So, the pressure goes up to about this clamp here,
and I've got.
So, the best I can tell is when I stick this thing in there,
static pressure is actually going down a little bit.
So, it looks like there's no benefit in cutting
the air stream closer here. Perhaps, if anything,
I should be giving it a little bit more room right here,
because that makes it quieter. For my next experiment,
I'll just shift this over a little bit to get more room
right here, and we'll see if that makes a difference.
So, now static pressure is a little bit over 11 1/2.
So, we're actually getting a little bit more static pressure
with this setup. Air flow is
about ten and a half, so air flows gone down a little bit.
Power consumption is down by about a watt.
So, I think what's happening is if I center this in here
a little bit more, then we have more air that can spin around
and around and around. And, just the centrifugal force
on the air spinning here will cause a little bit more suction.
But, having moved it like this, I don't quite get
the nice spiral effect, which I think reduces
air flow a little bit. So, next experiment,
let's try without a housing,
but I will need a few blocks, just to hold the top cover
of my blower.
We're now reading 13 meters per second here,
and 137 watts. So, it looks like
just letting the air come out on all sides
reduces the power consumption, and increases the air flow,
so that's a big win.
And, with no housing, static suction is
88 millimeters. So, removing the housing
means I get better air flow, but compared to having this,
I have less static pressure. And, I think
because I have a housing like that, I get much better
swirling of air around here, which adds to the static pressure.
Now, a wooden impeller running at high speed,
with no housing, that could be a bad idea.
So, for my next experiment, I'll just make the housing
a big square box.
Static pressure is ten and a half.
Air flow is 11.9,
and 145 watts. Must leak out a little bit more
of the housing.
Now we've got
12 at 142.
So, the air flow with a three-sided box
is still better than I have with this part,
and it could be fairly safe, cause I can make sure that
if the impeller were to explode, this is a fairly safe direction
for it to go. But, static pressure is still
less than I get with this, and static pressure is actually
quite important, because in a dust collector, a lot of times
most of the air flow is blocked from hoses and filters.
Well, given that there's no benefit
in cutting the air stream close here,
for my next experiment I'm gonna try to bend this enclosure
open a little bit, which makes for a bigger outlet
and more room around the impeller.
12 1/2 meters per second, 145 watts.
Well, maybe more like 11.3 average.
Now, I've just re-run all my static pressure tests
with this plate here, which lets through a limited amount of air,
and presumably the more pressure I have here, the more air
is actually also going through here, because
for a dust collector, with the filters and hoses and air
going through the tool, air flow is typically greatly restricted.
And, with that, the spiral housing initial,
and opened up a bit, had more pressure than I did
with no housing or a rectangular housing.
So, for a dust collection scenario, the spiral housing
is still beneficial versus a rectangular housing,
even though the rectangular housing will have more air flow
if there's no restriction to it. Now, just to illustrate
how much air flow is restricted in a dust collector,
I've got my anemometer hooked up near the outlet
of the blower here, and let's run it
when I disconnect the hose and the cyclone.
So, the hose is not hooked up to anything, let's turn it on.
So, right now this is reading 7.7 meters per second.
Let's take the hose off.
And, now we're up considerably at 10.2.
The cyclone has a lot of air resistance,
so let's disconnect the cyclone.
And, now we're at 30 meters per second.
And, now we're back to 10.
So, that tells me the cyclone makes for more air resistance
than sucking the air through these four small holes.
So, you're probably thinking, "Well, I have
too much constriction inside the cyclone."
But, if you look in here, I've got a big opening here,
and the inlet is also quite large.
The problem with the cyclone is the air spins around so much,
and it's go so much centrifugal force forcing the air
and the dust outwards, that it causes a lot of back-pressure.
It's like sucking air through a blower in reverse.
Now, just to illustrate this, I'm gonna put some junk
inside the cyclone, which intuitively you would think
will restrict the air flow even more.
And, now air flow's almost twice as what it was
with just the cyclone, because I prevented the air from spinning.
But, the cyclone isn't the only thing that restricts air flow,
so now let's just have the hose and no cyclone.
And, air flow now is actually less than with just the cyclone.
So, this hose has got more air resistance than the cyclone.
So, I hope this demo with my home-made dust collector
helps you understand how static pressure
really dominates the system, because by the time
you've sucked the air through hoses and cyclones and filters,
and through the machine itself, the CFM rating
of your dust collector blower really doesn't matter.
It's how much pressure you can get that actually determines
how much air you're gonna suck through the whole system.