Lost suction!!! Please help.

[painterman]

Painterman:
To answer your question about the losses through a separation system.  They can be huge, depending on flow.  At max flow they can be as large as 60% of the unit?s capacity.  And that is what you are feeling with your hand testing.  But under normal conditions, they are probably closer to 10 ? 15% of total capacity.  I agree with others that your issues are likely not with your top hat system.

Here is my experience with separator losses.  I built a trash can separator for my Harbor Freight 2HP unit and measured the actual vacuum at two locations with a gage, just like you did with your hands.  You can see from the images below, that at the separator inlet under no load, the vacuum was 1.75" of W.C, but at the blower inlet under the same conditions, it was 6.0" of W.C.  So at maximum flow conditions, the loss through the can was 4.25" or almost 60% of the total capacity of the unit (which is about 7.3? of W.C.).  I did smoke testing on my unit, so know there are no leaks and the losses are real. 

The reasons for my losses are due to the friction loss through two 90deg elbows, the 45deg wye, plus other friction losses from the air moving from the can back into the blower suction pipe.  Wood Magazine just did an article on calculating losses in a DC system under normal conditions (350 CFM).  If I use their spreadsheet, I come up with a predicted loss for my separator system of 1.05? of W.C.  But that is at normal flow conditions.  At max flow conditions for my unit of about 650 CFM, that figure translates to 3.62? of W.C. which is not too far from the 4.25? I measured.

In Wood Magazine?s 3/2008 article, they show your Grizzley1029 as having  something like 900 ? 1100 CFM capacity at max flow conditions and a max static pressure of 9? of W.C. ? far superior to my HF unit.  So you will see even larger differences of loss between max and normal flow conditions.

So are you saying that everything is normal and that my test was really an unreliable test?  You say that I will see an even larger differnce  of loss between max and normal flow conditions.  Is that bad?
Thanks,
John

[bill70j]

Painterman:
To answer your question about the losses through a separation system.  They can be huge, depending on flow.  At max flow they can be as large as 60% of the unit?s capacity.  And that is what you are feeling with your hand testing.  But under normal conditions, they are probably closer to 10 ? 15% of total capacity.  I agree with others that your issues are likely not with your top hat system.

Here is my experience with separator losses.  I built a trash can separator for my Harbor Freight 2HP unit and measured the actual vacuum at two locations with a gage, just like you did with your hands.  You can see from the images below, that at the separator inlet under no load, the vacuum was 1.75" of W.C, but at the blower inlet under the same conditions, it was 6.0" of W.C.  So at maximum flow conditions, the loss through the can was 4.25" or almost 60% of the total capacity of the unit (which is about 7.3? of W.C.).  I did smoke testing on my unit, so know there are no leaks and the losses are real. 

The reasons for my losses are due to the friction loss through two 90deg elbows, the 45deg wye, plus other friction losses from the air moving from the can back into the blower suction pipe.  Wood Magazine just did an article on calculating losses in a DC system under normal conditions (350 CFM).  If I use their spreadsheet, I come up with a predicted loss for my separator system of 1.05? of W.C.  But that is at normal flow conditions.  At max flow conditions for my unit of about 650 CFM, that figure translates to 3.62? of W.C. which is not too far from the 4.25? I measured.

In Wood Magazine?s 3/2008 article, they show your Grizzley1029 as having  something like 900 ? 1100 CFM capacity at max flow conditions and a max static pressure of 9? of W.C. ? far superior to my HF unit.  So you will see even larger differences of loss between max and normal flow conditions.

So are you saying that everything is normal and that my test was really an unreliable test?  You say that I will see an even larger differnce  of loss between max and normal flow conditions.  Is that bad?
Thanks,
John

John:
I am saying that if your system is hooked up, then the test you did would give a different result - you would feel much less difference between the suction at the separator inlet and the suction at the blower inlet.  That's because with the system hooked up, the flow is much less due to the friction loss through all the parts of the system, starting from the machine you're sucking on back through the flex hose, the ells, the wyes, the blast gates, the reducer, and the ductwork.  So if you do a test with all of that hooked up, your flow will be reduced from your max blower capacity of 1100CFM to much less that that, say 550CFM.  The pressure drop through your separator at 550CFM vs the loss at 1100CFM would be four times less.  And I am saying that the bigger your blower, the more discrepency there would be between your original hand test and the real result with the system hooked up - not a bad thing, just a different result.

[painterman]

Well, I have done it.  I changed over to 6 inch pvc and a new two bag 3 hp dust collector.  This thing really sucks.  That is it does well without the thein tophat separator.  The minute I install that into the system, I loose pressure, and quite a bit.  My down draft table, with out the separator, almost would hold the wood down like a magnet.  With the separator the hold down power wasn't even noticeable.  Every tool I tried was the same result, much less suction.  So I guess that unless there is a design flaw in my tophat separator, then I will just stay with the two bagger and not use the separator.  With two bags I can go longer between dumping my sawdust.  Any ideas?
Thanks,
Jon

[WayTooLate]

Painterman -
I sympathize with your decision. 
My commercial woodshop started using separators because our large, multi-bag dust collectors are upstairs and a very inconvenient to clean and dump.  (Out of sight, out of mind and everyone will avoid the 'dirty work') 

By using the separators (between the machines and trunk lines), we keep the waste on the floor in 'Brute' cans on wheels - nobody complains about dumping them. 

However, we do have suction losses.  Our measurements are not as severe, though.  Using a manometer, we measure about 1.5" of suction loss.  This adds up with several separators connected.  We have the trade-off that the overall system flow is reduced, but since it has very little waste in the air stream, we can tolerate the reduced air flow. 

The losses you are describing seem much greater than normal.  I am wondering if there is something that you have overlooked in the design or something else that is compromising your performance?  Your empirical measurement of sticking your hand over the hose should detect reduced suction after the separator, but not to the level you describe... 

I hope you get this solved.  Using the separator is a MUCH, MUCH better way to work rather than dealing with bags! 

- Jim