DUST COLLECTOR main line drop downs

[Temp626]

I am in the design phase of ductwork planning and have a question or two for the forum.


General info:
- The collector is the PennState Tempest 1535 w/ 7" inlet. The machine is rated at 1700 CFM through the collector. I will be using the 7" - 6" reducer that is supplied with the machine. That was recommended by the support staff at PennState. My main trunk line will be 6" with some 6" drop downs and some 4" drop downs.




My main question is, should the "y" portion of the fitting that creates the drop down come off the main trunk horizontally and then transition to vertical downward, OR can the "y" portion of the fitting come off the main trunk vertically downward right away.


I read somewhere that you should come off horizontally so that the bottom of the main trunk doesn't have spots for chips/dust to settle down into like the vertical "y" drop down.


I know this is a bit confusing to picture, but any help will be appreciated.


Thank you.

 

[Bas]

If I read your question correctly, then you should point the Y portion down, like this:


You could rotate the Y fitting 90 degrees (so that the in and two outs are in the same plane), but I don't see any advantage to that, not unless you wanted to create a split (instead of a drop).

I don't think you'll have any issues with chips/ dust setting in the duct work.

 

[Bill Clemmons]

Tom, I'm not sure I completely understand your question, but I'll give it a shot anyway. If I miss the mark, feel free to tell me so.

Assuming the horizontal duct along the ceiling will continue beyond the drop down: Put the wye in the horizontal duct and turn the angled portion down. Then put a 45* sweep/elbow on the angled branch of the wye to complete the 90* down turn for the drop down.

If you want to put a drop down at the end of a horizontal duct, use a 90* sweep/elbow.

HTH

Bill

Edit: exactly as Bas has pictured above, then add either a rigid 45* elbow to complete the 90* down turn, or flexible hose to connect to the equipment.

 

[Alan in Little Washington]

The big concern with drops coming off the bottom is that dust may collect in any intermediate drops between the one being used and the the DC. That is typically only a concern if you have an under-performing DC or too extensive of a duct system with too much SP loss and insufficient velocity. Depending on duct orientation, size of your dust/chips, etc. you need a velocity of roughly 2500 - 4000 fpm. (4000 fpm is most often quoted because it covers all situations.)

If the velocity of the dust is too low to keep chips suspended in the air stream, they could settle out in intermediate drops and the duct. If that happens a little, occasionally opening the intermediate drops should clear them out. If drops regularly clog that way, you have bigger issues than the angle of the wye- your DC is WAY TOO SMALL!!! (or your duct too large, or both)

I angle my wyes which ever way results in the most direct and straightest piping runs, and least SP loss. Fortunately, the mains (and the DC) are below my machines.

 

[Temp626]

Thank you all for the help. I don't plan to go more than 6" for the trunk lines. You confirm pretty much what I was thinking, that coming off the bottom would be insignificant as long as the velocity is sufficient, and that additional pipe/fittings only degrade the system..... Thanks again.