Thoughts on larger outlet diameter than inlet for _blower_ based system?

[phallstrom]

Hi all -

I have the Dewalt planer that has it's own blower. I've built my system and it works great. No chips escape. 4" inlet and outlet. 20" diameter baffle.  I notice when I flip it on that there is [obviously] some positive pressure on the garbage can.

Got me wondering what would happen if I enlarged the outlet to 6" diameter? Would that be better or worse? Easy to try, but kind of hard to revert if I'm wrong.

I realize this isn't the usual setup (blower vs vacuum) but hoping someone might have some thoughts...

Thanks!

[alan m]

that's an unusual set up. is the outlet flush witht he top of the cart and the planer sitting on top. is there enough room for the air to escape.
I would try raising the planer a fit first then  try it again.

your inlet looks like it is going into the top of the rectangular inlet.


you have nothing to lose by widening the outlet. it should help but it would be a fine line  between perfection and allowing bypass.
have you a pipe in the middle  upder the outlet

[phallstrom]

The outlet is 1/2" proud of the top of the baffle. And it extends down into the baffle leaving about a 2" gap till the bottom portion.

There may or may not be enough room for air to escape. Something I'm testing and will raise it up a bit if necessary (the planer has "legs" so it looks more trapped than it is).  I've noticed the pressure even when the planer isn't on it though.

Inlet goes into the top, and immediately into a right angle so air/chips shoot in horizontally as they should.

Can you clarify what "allowing bypass" means?  Does that mean that if the outlet hole is too big air/chips can make it into the center of the baffle and get pushed up and out before having a chance to fall down through the slot?

Alternatively.. if it works fine as it is now, is there any reason to worry about a little pressure? Like.. will that strain the blower?  It doesn't seem excessive (not like if I capped it completely).

[alan m]

I don't have much experience with plastic drums  and none with push seperators.

what do you mean by pressure. is the barrel expanding. I don't think it should. it is a very open system and should  allow the pressure out the top  rather than down into the barrel.

[phallstrom]

I think a little. You know I really ought to go do some measurements.

Still interested in the overall theory of having a bigger outlet than inlet, but really just curious.

Dang thing works amazingly well right now!

[Schreck]

That planer has a 2.5" blower discharge, so you have already up-sized to 4", which reduces your velocity.  Increasing the outlet diameter to 6" would reduce pressure drop, but it is a very short length, so there might not be much benefit and the risk of increased bypass is a reason not to do that. 

If you are inclined to mess with success, consider eliminating the 90 degree ell at the separator inlet. OTOH, if it's working well, declare victory!

[bbain]

hey, look at that, someone else with a push separator on a DW735! Works great doesn't it?

I have mine with 4"in and out. Yes, there is some pressure in the barrel.  Mine is a tophat and first time I tried it, it popped the tophat off the plastic garbage can.  I have locking tabs that fit under the rim of the can now to keep it on.

I don't think you need to worry about the blower, there is far more load on the motor from cutting the wood than there is from spinning the blower fan.

[phallstrom]

bbain - That is great to hear about your experience. And yeah.. it works soooo well.