[DaninVan]

Dust collection :
On a horizontal 4" ceiling mounted run (PVC pipe)., when you install a 4" wye in the run, is there any problem with the 45deg. hub being on the bottom of the ftg. rather than pointing off to the side (laterally)?
I'm a bit concerned that sawdust from farther down the line might try and build up in the interior of the intersection. My preference would be down, but canted off to the side by 45deg. might also work for me.

 

[Stick486]

no..

 

[DaninVan]

"No" as in it's not an issue pointing down (6:00 o'clock)?
Excellent. I'm going with that unless the tribe votes otherwise.

 

[sunnybob]

If the main use is the top run, then sawdust will collect in the lower section of the pipe. If the lower section is rarely used then the dust will get pretty deep in there. That may cause you problems when you do use the lower run.
I would have the main machine connected to the lower, with the "Y" sloping towards the collector. Almost nothing will stay in the horizontal run as the lower draught will act as a venturi and suck it clean.
If you can fit blast gates close to the "Y" on each leg, even better.

 

[Cherryville Chuck]

If one side of the Y is pointed down and that side is not open then the lack of air movement could cause a vortex at that spot which could cause some of the larger particles to drop out of suspension down the dead side. If there is enough buildup at the bottom of that side then it will plug up once no air can move to clear the jam. You would be better off to always keep both sides open if you do that.

 

[sunnybob]

But that would mean 50% of your extraction is wasted down the open leg.
A blast gate at the joint will solve all problems. If thats not practical then use the downward pointing one as the main.

 

[DaninVan]

Hmmm....there seems to be some dissent here(?).
Does rotating the 45deg. hub to 3:00 o'clock (or 9:00 o'clock), or 4:30, resolve those issues?
I'm trying to avoid adding extra fittings, and their decrease on the airflow's efficiency.
The trouble with putting the blast gates up near the wye on the ceiling is I can't reach them...8' ceiling.
Bob; I've seriously considered running the horizontal at floor level, with the wyes facing 12:00 o'clock.
Trouble is it'll be buried behind a long run of cabinets and machine positions. Also, the dust piping would have to accommodate the machinery*. Other than that it makes way more sense.

*RAS, SCMS, router table, sanding area

 

[sunnybob]

Dan,
If there is a pipe hanging down and sawdust is flowing across the opening at the top, the law of gravity applies. It may take a while, but that pipe will fill. If the down pipe is left open, some dust will fall on the floor or into the machine and you will lose 50% of your air flow.
If the pipes are sideways, theres not so much gravity, but there is a vortex which will still suck some dust into the dead leg.
If you use each leg often, or the down leg is is the most often used then there is no problem. If the down leg is to a machine that is rarely used, and the across pipe is to a machine in daily use, the problem is obvious.

My preference would be to fit a blast gate on each run at the Y (I have seen flap over Y joints, that incorporate the gate in the Y), and modify the gate (s) so it / they could be opened and closed with a stick, just like a high window in a classroom. this would give you maximum efficiency on all legs of run.

Low level runs work. My first system was 4" run at knee height behind the machines, but as I got more machines it became stupidly expensive to buy all the gates so i downsized to 62 mm (2 1/2") throughout. Still run at knee height.
I have all my 5 gates located in a "mission control" area so I just open the one I want and make sure the rest are closed.

 

[Stick486]

low CFM flow is the generator of issues..
turn on the DC...
open the gate and it should clear..
still an issue (stuff collecting in the Wye)..... crack open the gate at that fitting while the system is in use elsewhere...

I knew there was a good reason for running the trunk line at base board height level...
less lift...
less pipe...
less fittings..
higher efficiency..

 

[DaninVan]

In a perfect shop, Stick, I'd do that in a heartbeat, but for the reasons I listed in my previous post, it's not practical in my configuration.
I paid attention to the system that the local high school has in their woodworking shop (we do our woodworking club mtgs. there), it's pretty complex but the main run is about 10' high! The collector is outdoors.