DustKop DC?

[®smpr_fi_mac®]

It was originally built for use in a paper shredding operation. That's what the salesman told me after looking up the serial number on this unit.

[®smpr_fi_mac®]

What does SP mean?

Are you guys saying that it might be unwise to run this thing with no load on it? That I might need a blast gate just to increase resistance?

Why might that be?

[®smpr_fi_mac®]

The 16.5" diameter is an estimate. Once I have some weather stripping on hand and peel off the impeller cover I'll get a proper measurement.

The impeller on the upper left side just clears the housing so I measured drum the edge of the housing to the center of the impeller.

[®smpr_fi_mac®]

Oh, I don't think this impeller qualifies as a squirrel cage style-- the impeller is open on the outer circumference, unlike the fans in a squirrel cage (furnace blower).

Does that make a difference?

The vacuum this thing creates in front of the intake is really impressive.

[TDKPE]

It was originally built for use in a paper shredding operation.  That's what the salesman told me after looking up the serial number on this unit.

Not really relevant, since there's no way to know what the actual flow resistance might have been.

What does SP mean?

Are you guys saying that it might be unwise to run this thing with no load on it?  That I might need a blast gate just to increase resistance?

Why might that be?

Yeah, sorry.  Static Pressure.  The amount of 'suction', or vacuum, or how hard it pulls on the air, measured in inches of water (partial vacuum pulls water up one side of a U-curved tube - the height difference between the two sides is the SP measured in inches of water, aka 'water gauge'), though mechanical gauges are normally used.  But you can make your own with just a bit of nylon tube.  https://www.google.com/search?q=u-tube+m...00&bih=919

Centrifugal blowers (including squirrel cage blowers) work opposite to axial fans in that when you restrict the air flow, the power required to drive them goes down.  Do that to a common fan, and the power required goes up, or in the case of common cheap fans, they just slow down. 

That's why your vacuum cleaner speeds up when you block the air hose - it unloads the motor.  The air is just swirling in a circle (more or less) inside the scroll housing, and not being accelerated and discharged which takes more power.  Centrifugal water pumps work the same way, too. 

But that also means a centrifugal blower that's designed for a minimum SP can be overloaded if allowed to flow too much air.  So do check the current on the motor when connected to whatever you're going to connect it to, to make sure the motor current doesn't exceed the nameplate value.

The 16.5" diameter is an estimate.  Once I have some weather stripping on hand and peel off the impeller cover I'll get a proper measurement.

The impeller on the upper left side just clears the housing so I measured drum the edge of the housing  to the center of the impeller.

Then that's a really large diameter impeller for such a unit.  Still sounds like it was built for some high flow resistance application, where it needed to pull hard to get enough air to flow to suit the manufacturer's requirements.

Oh, I don't think this impeller qualifies as a squirrel cage style-- the impeller is open on the outer circumference, unlike the fans in a squirrel cage (furnace blower).

Does that make a difference?

The vacuum this thing creates in front of the intake is really impressive.

Same principle.  They're both centrifugal blowers.

[®smpr_fi_mac®]

Wow. Things I had no clue of.

As usual!

And, as usual, you've explained them in a very clear manner. Thanks. I'll look into it.

I'm not sure how I'll check the amp draw on the motor. I have a Fluke meter that can be used to measure amps, but I think I'll need to open up the cover on the motor to find the leads to connect to.

I've built DIY manometers with water and food coloring to balance carbs on a bike. Your reference makes sense to me.

[TDKPE]

I'm not sure how I'll check the amp draw on the motor.  I have a Fluke meter that can be used to measure amps, but I think I'll need to open up the cover on the motor to find the leads to connect to.

Don't try the DMM - unless it has an actual inductive clamp specifically made for that purpose.  It'll blow the internal fuse on start-up.  And you'll have exposed leads.  Unless you have something like this:  https://www.amazon.com/Extech-480172-AC-...T9MACWPYS2

Better to use even a cheap clamp-on ammeter like this one https://www.harborfreight.com/clamp-on-d...95683.html will get you in the neighborhood.  But you need to expose a single lead (hot or neutral; doesn't matter) to get a reading.  You can also see starting current, which will be an eye opener.


Another option is a Kill A Watt unit, which measures current, voltage, wattage, volt-amps, and some other stuff.  https://www.amazon.com/P3-P4400-Electric...=killawatt  Or this one:  https://www.amazon.com/P3-International-...=killawatt

Very handy for many things, in fact, and quite cheap.  No adapters or exposed wires needed.  But current is limited to 15A, since it all goes through the device itself.  Mine can handle startups on my '2 hp HFDC', though it can't read the starting current, and as long as I keep enough blast gates closed to not load the motor beyond 15A.  I use a clamp-on ammeter for that. 

But the Kill A Watt can show you things like volt-amps and power factor, which can be instructive for understanding how large motors with light loads actually don't spin your electric meter as much as an ammeter would suggest it does.  Like a dust collector running with the blast gates closed.  

[Dan Moening]

My guesstimate ...

Using this schematic:





The center of the impellar (@ 73 13/16") less the height of the table (58") gives 14 13/16".

The fan shroud is less than half that distance ... say 6" (double that for full diameter of the fan shroud = 12")

Subtract an 1" per side for clearance around the impeller ... leaves approximately 10" impeller.

[TDKPE]

And then there's that 13" horizontal dimension to the impeller center, which looks to be a bit more than the out-to-out of the scroll housing.  Assuming it's to scale.

[®smpr_fi_mac®]

The shadows inside the housing played tricks on my eyes. Hooking my tape on the end of a blade, the impeller reads closer to 10" in diameter.

Does that sound more feasible?