DC3300 Dust Collector

[robinson46176]

Sit it outside with the bags removed.


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Actually it would be easy to just attach an adapter to the upper bag or filter and run a 4" hose outside and leave it otherwise intact. A dryer vent would handle it.


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[JPG]

Actually it would be easy to just attach an adapter to the upper bag or filter and run a 4" hose outside and leave it otherwise intact. A dryer vent would handle it.


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I like the 'simpler' one more gooder!:D

[dusty]

The major difference between the DC3300 and a ShopVac is that the DC3300 is designed to move air and not develop suction. That is why a ShopVac can lift water and other heavy debris and a dust collector can't. Conversely, a ShopVac cannot move large volumes of air. Put your hand over the hose on your ShopVac, and the motor changes pitch as it whines and complains because it is struggling to maintain a certain airflow but is developing pressure (suction) instead. Block the opening of the DC3300, and there is not as noticeable a change in pitch - the fan chugs away and since it cannot develop much pressure, the air flow is reduced.

With all three ports open (or one big 4" port), the DC3300 can move 330 CFM as stated. When you restrict the opening to a single port the airflow is reduced as a function of diameter. However, the air velocity increases which is why the DC3300 appears to have increased suction (velocity head).

A 2 1/2" hose is approximately 1/3 of the surface area of a 4" hose, so the airflow is reduced to 1/3 of maximum. Open a second port and you now have 2/3 of the maximum airflow, but still only 110 CFM at each port (not 165)

Now add hoses. The resistance in the hose will further reduce the airflow. PTWFE is correct in that the airflow goes from 110 (with no hose) to 107 to 100 to 95 as you add hoses. However, although the airflow is essentially the same, the velocity in each hose is significantly lower than if only one hose was attached. This is why I don't understand how opening a port will improve airflow, as you are reducing the velocity head.

Have I thoroughly confused you all, now?

You have slightly different numbers than I but I do not believe we disagree in principle. Do we agree that regardless of the number of ports (open or closed) the DC3300 attempts to move 330 CFM out through the filter bag?

and

Do we agree that if the entrance port is 2 1/2" in diameter, the velocity of the air entering that port will be CFM/Area (expressed in SqFt) and therefore the velocity must be 9666 Ft/Min (ignoring all theoretical losses). If it is not then the DC3300 does not move 330CFM.

[michaeltoc]

You have slightly different numbers than I but I do not believe we disagree in principle. Do we agree that regardless of the number of ports (open or closed) the DC3300 attempts to move 330 CFM out through the filter bag?

and

Do we agree that if the entrance port is 2 1/2" in diameter, the velocity of the air entering that port will be CFM/Area (expressed in SqFt) and therefore the velocity must be 9666 Ft/Min (ignoring all theoretical losses). If it is not then the DC3300 does not move 330CFM.

The key word is ATTEMPTS. If the inlet is blocked, the fan is starved and cannot push 330 CFM - It can only push about 110 CFM.

The velocity would theoretically be 3227 ft/min (The airflow is 110 CFM, not 330)

[hdtran]

The specs on dust collectors tend to be optimistic. The CFMs given are typically CFM through the impeller (fan) with almost no upstream obstruction, and either no downstream obstruction, or 'clean bag.'

What is more useful is a flow rate vs vacuum curve. Almost no one will give you that, unfortunately. See the chart at ftp://woodworker.com/dustcoll.pdf as an example of flow rate vs vacuum curves.

Shopvac impellers are designed to provide high suction at relatively low flow rates. Dust collector impellers, vice-versa.

I would assume, given that the DC3300 design is fairly old, that the 330 CFM rating is not 'usable 330 CFM', but in fact, 330 CFM with no upstream obstruction and minimal downstream obstruction.

Your system may be restriction-limited upstream, that is, the amount of pressure drop through your piping upstream is limiting the CFM, not the impeller/motor. If that is the case, opening up an extra port would increase the CFM through the motor. I doubt that this would increase the CFM through your piping, though. Flow rate through piping is driven by pressure drop (how much vacuum can your impeller suck). The bigger the vacuum at the DC3300, the greater the flow rate through the piping. I cannot imagine any reasonable scenario where a lower pressure drop through the pipe (business end of the collector through plumbing to DC3300 port/octopus) would result in greater CFM through your pipe.

Of course, I'm just theorizing

[dusty]

Michael, I still do not understand. It is advertised that the DC3300 delivers 330 CFM (thru the filter). To do that, it must draw that 330 CFM in thru the open port/ports. If there is only one port open, the entire 330 CFM exhaust thru the filter must be drawn in thru the port.

I understand that these absolute numbers cannot be achieved but I do not understand why you say that the flow will be 110 CFM and not 330 CFM.

[RobertTaylor]

ya know what i like about my dc3300 dust collector is that it sucks the sanding dust right out of the air when sanding in the lathe configuration. the chips from turning mostly fall to the floor. but it only takes a few minutes to clean them up with the hose and the mrs. is happy that i am not tracking them upstairs and the sanding dust is not being sucked into the furnace and redistributed throughout the entire house. bottom line is it works well and if it did not i would have to buy a different brand with more cfm's to be able to work in the basement. i think cfm ratings on dust collectors are like horsepower ratings on cars. fewer horses still get me there and generally eat less hay, i mean gas.

[michaeltoc]

Michael, I still do not understand. It is advertised that the DC3300 delivers 330 CFM (thru the filter). To do that, it must draw that 330 CFM in thru the open port/ports. If there is only one port open, the entire 330 CFM exhaust thru the filter must be drawn in thru the port.

I understand that these absolute numbers cannot be achieved but I do not understand why you say that the flow will be 110 CFM and not 330 CFM.

330 CFM is the maximum airflow with all 3 ports open (or 1 a 4" port). When you close down the ports you reduce the airflow.

Try this: open all 3 ports and fire up the DC. Press on the bag. You'll see that it's quite firm. Now close off 2 ports and feel the bag. It's now much softer because the airflow (and the pressure) is reduced.

[michaeltoc]

Or let's look at it another way:

A city water main can put out upwards of 1000 GPM of water through a fire hydrant. Connect a garden hose to that same city water main and you're lucky to get 10 GPM. The city water system is CAPABLE of putting out 1000 GPM, but you've put a major restriction in the line and this reduces the flow. Now add 100 garden hoses, and voila - 1000 GPM!

[JPG]

If I 'heard' correctly, the 330cfm is a design 'constant!'.

http://www.shopsmithacademy.com/SS_Archives/SS109/SS109_Dust_Collection.htm