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We be ignoring static pressure! The impeller will move a maximum volume at an optimum static pressure. I do not know what open port count provides that, but apparently it is 'more than one'. Flow resistance will also affect the static pressure. The static pressure will vary at different points in the 'plumbing'. I believe the static pressure will be greatest nearest to the impeller and decrease through each different shape in the 'plumbing'. A long run will have a different static pressure at the ends, and a "T" or "Y" or an elbow will have different static pressure at the in/out ends.

This implies that the 'plumbing' will alter the static pressure at the impeller and therefore each installation will react uniquely.

Wanna weigh in on this Mike? (Any body heard from him lately?????)

The only plumbing in the system has been the three hoses (usually only one with the two ports closed).

This exercise began when I was experimenting to improve dust collection at the table saw. I connected a second hose and was experimenting with methods to reduce the dust that collects top side. I noticed that the level of debris that collects on the carriage is variable.

Thanks for your inputs. They have been helpful. Charlese, your last input helps immensely.

The 330CFM capacity of the DC does get split sorta equally between the three ports to become 110CFM at each port. From this I conclude that with one port blocked, the 330CFM is shared producing 165CFM at each of the two hoses. Velocity must change but I don't detect that at all.

Additional Comment: This turns out to be a very technical issue. Much more complex than one might think. What I am attempting to do is improve on general cleanliness and will not necessarily improve the quality of air. I do not want to be covered with saw dust and small chips when I finish a project at the table saw (which is what started my quest).

I have discovered this additional source of information that I would encourage everyone to read. The dust collection solution is much more complex than just adding a hose or two. What I have posted here before, on this subject, amounts to gross over simplification.

dusty wrote:The only plumbing in the system has been the three hoses (usually only one with the two ports closed).

This exercise began when I was experimenting to improve dust collection at the table saw. I connected a second hose and was experimenting with methods to reduce the dust that collects top side. I noticed that the level of debris that collects on the carriage is variable.

Thanks for your inputs. They have been helpful. Charlese, your last input helps immensely.

The 330CFM capacity of the DC does get split sorta equally between the three ports to become 110CFM at each port. From this I conclude that with one port blocked, the 330CFM is shared producing 165CFM at each of the two hoses. Velocity must change but I don't detect that at all.

Additional Comment: This turns out to be a very technical issue. Much more complex than one might think. What I am attempting to do is improve on general cleanliness and will not necessarily improve the quality of air. I do not want to be covered with saw dust and small chips when I finish a project at the table saw (which is what started my quest).

I have discovered this additional source of information that I would encourage everyone to read. The dust collection solution is much more complex than just adding a hose or two. What I have posted here before, on this subject, amounts to gross over simplification.

I haven't read the additional source yet but will. I just wanted to add this thought while I still had it. I believe that the difference is the amount of pressure it takes to push the collected air through the bag. I also believe that this "open intake" is no longer a factor when you use an open outlet like when you vent a DC directly outside and do not run it through a bag where it has to force its way out. I think that the small single closed off intake starves the fans ability to build enough pressure in the bag to force enough air out through the dust pack.
Am I making sense here? I just got up.
On my old shoe machinery which uses all manner of dust collection I was always able to vent directly outside which I believe is why I had not observed the extra open intake factor before.


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Well my DC starting making a noise and I thought I might have gotten something in it that messed up the impeller but took it apart and found the bolt holding the impeller came loose so put some locktight on it and put it all back together. question is anyone that has taken theirs apart what did you use for the seal on the motor intake and then the hose intake area. Did you order new seals from SS or did you find something that works fine.

dusty wrote:I am not sure I understand. It seems to me that if the impeller is attempting to move a certain amount of air and if that air can be drawn though only one port then the suction at that port should approach maximum. That does not seem to be the case. What do I not understand?

The DC3300 is said to move 330CFM. How many CFM can be moved through a single DC3300 port? If the answer is 110CFM then I think I understand.

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?

JPG40504 wrote:We be ignoring static pressure!

JPG is on the right tack here. Any impellor has a performance curve similar to the power curve on a car engine. Think of torque and horsepower at a given RPM. If you choke off the available airflow enough, the impellor will stall and produce no airflow, even if it keeps spinning. That is the reason for using wyes and long ells in the ductwork instead of tees and short ells. It is not to prevent chip build-up/jams (although it helps), but rather to make smooth airflow which reduces static pressure which increases (usually) airflow.

Try sucking coffee thru one of them little mixer straws .... you go thirsty. Now, try sucking it thru half a dozen .... dang, that stuff's hot! haha

robinson46176 wrote:I think that the small single closed off intake starves the fans ability to build enough pressure in the bag to force enough air out through the dust pack.

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Yes - That is exactly what is happening. I would guess that direct venting eliminates the bag resistance, lowering the static pressure and possibly increasing the airflow.

I have a small flow meter, and will run some "tests".

michaeltoc wrote:Yes - That is exactly what is happening. I would guess that direct venting eliminates the bag resistance, lowering the static pressure and possibly increasing the airflow.

I have a small flow meter, and will run some "tests".

Keep in mind, the static pressure at the output is positive, while at the intake is negative.

Re open venting, the 'back' pressure created by reducing the output flow capacity is illustrated by the fact ss increased the area(bigger bag) to accomplish the finer filtering capability. That was to maintain the cfm while providing smaller particle filtering capability. Open venting diminishes the 'back' pressure thus allowing maximum cfm all other things being equal.

I be curious how open venting can be accomplished with the DC3300!;)

I went and read the “additional source” page. Well, most of it... Dang, and people accuse me of using too many words.
I didn't study any figures closely but I didn't see any of the theory that I would disagree with in general. Sadly it takes dust collection to the level that I would maybe set my shop on fire then go out back and shoot myself rather than try to keep woodworking...
I believe that “for me” I will continue my plan to vent my dust collection outside. This is a 105 acre farm and I have no close neighbors. The discharge point will even be over 400 feet from my house and where the very prevailing wind out of the west will carry any floating dust away from the shop and house both. The discharge point will be in a tiny dense woods close behind the shop.
I'm planning the blower outside in a 4'x4' shed as well as the separator. I want a simple separator just to protect the blower from hard things. More than once over 20 years in the shoe shop I had to walk outside to retrieve a shoe sole I was sanding. That was a 6” system, cast iron blower housing with a steel radial impeller.
Yes it will require make up air and yes it will have a heating and cooling cost but that will be nothing (remember I have 20 years experience doing this) compared to the cost of some of the proposed cures. Since my primary heat source in actual cold weather is wood the heat cost just isn't really a factor. The air conditioner will only be used in very hot weather and the rest of the year I like things opened up and use several big squirrel cage fans. These are much larger than todays furnace blowers. They run slowly and quiet but move “a lot” of air.
Of course the real problem stuff is the “smoke” looking dust that tends to form a layer in the air at just the wrong level where we breathe it. While in my old leaky shop a 20” box fan with a duct taped filter on it seemed to be enough I now want a lot more. I will likely build my own since anything with enough capacity is just out of sight $$$$. A BIL who built his own small unit for his nice smaller shop commented that if he stops working the “cloud” goes away fairly soon. I have decided that I don't want a cloud to go away... I don't want it to form. That will require moving enough air that venting outside in the winter probably would not be at all practical but decent pleated filters are fairly cheap. In warm weather I would just vent it directly outside. In winter a heat exchanger “may” be do-able since only very fine dust would be involved.

Now for another thought in the mix...
Those of us who have reached geezer status should all remember the old oil-bath air cleaners on cars. Most of my old tractors use them. They will capture very fine stuff. A huge oil bath cleaner may not be at all practical but on a lot of old shoe machinery the big dust collection blowers discharged into a big water bath air cleaner then back into the room. I never used one but my father had owned one. He said that it worked very well but he did mention the words “mud pies”.
The concept may well be worth investigating.
Some paint booth air scrubbers may also yield good ideas.

[quote="JPG40504"]
I be curious how open venting can be accomplished with the DC3300!]



Sit it outside with the bags removed.


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