Corrugated v smooth wall piping for DC

[W Canaday]

Okay ... folks had me just about convinced to buy 4" pvc piping for the major portion of my DC waste runs and then I read a posting that said, in essence "Nope ... you NEED the turbulance in a corrugated pipe to keep the dust & chips in suspension."

So what's the real skinny on this? (I was at the orange box today pricing PVC stuff out ... even with pricier fittings, it is roughly comparable in cost to the Woodcraft / Rockler solutions. I especially liked the long curve Y pipes because of their very gradual entry to the straight pipe).

What I am presently envisioning is to use PVC up to the point where a piece of corrugated needs to be attached ... using corrugated only for the final few feet.

What say you? The layout of my shop will probably be pretty static (things will probably remain near their present location but move a little from time to time to accomodate larger stock / larger projects.) so the permanence of PVC is not a huge concern. I can locate all of my equipment around / near an outside wall so I don't plan on lofting the dust overhead until it actually hits the dust bag. The pipe can ride the floor and eventually be covered with shelving, cabinets and benches.

I am thinking that, with fairly short runs (max 30 ft), there probably isn't any effective difference. But that is a wild, wild guess.

Again ... what say you?

Bill

[Lew Hodgett]

See what happens when you start thinking.

Laminar flow happens at relatively low flow.

Turbulent flow starts in a smooth walled tube at relatively low velocity, from memory somewhere around 4-6 ft/sec.

Turbulent flow is what you want.

Use smooth walled tubing where possible, flex wher necessary.

Want to save a few $, use ABS (black) pipe where possible.

Lew

[W Canaday]

So laminar flow is simply a non-issue in a DC system?

Bill

[DonkeyHody]

I believe you need VELOCITY in your pipe, not turbulence. Velocity creates turbulence, but turbulence is the enemy of velocity. I don't think you need to do anything to increase turbulence. Besides, I don't envision the chips sailing along suspended in the air very far. I think after a short distance they fall out and are scooted along on the "floor" of the pipe. You need enough velocity to keep them moving right along so they don't pile up.

I work in the dredging industry. The principles involved in keeping sediment moving in a pipe full of water are similar to the principles in keeping chips moving in a pipe full of air. But in this case it IS important that the sediment remain in suspension because of the long distances it must travel (sometimes several miles). Still you often get a "moving bed" of sediment on the bottom that has fallen out of suspension. Many years ago, they ran some controlled tests to see if deliberately increasing the turbulence by using spiral welded pipe would improve sediment transport. They found that the increased turbulence reduced velocity and hurt transport.

DonkeyHody "Even an old blind hog finds an acorn every now and then."

[rllipham]

Keep the velocity. If you have a decent DC you do not have to worry much about velocity that is unless you plan to send 3' pieces through the system.

Remember:

It's not "How much wood could a wood suck suck if a wood suck could suck wood." or something like that.

You can go with PVC. I purchased the PVC thin wall sewer pipe at Lowes. The borg did not have them. A plumbing supplier should help. THis was the cheapest and easiest way for me to go.

I put 6" for all horizontal runs and reduced to 4" for the vertical runs and then used the corregated hoses from the blast gates.

I also run the piping through a drop box prior to the DC. I clean the DC about twice a year.

The sewer PVC is lighter and simply easier to cut and handle. Hope this helps.

[Rob V]

I just did my shop w/ 6" PVC runs every where to just about every machine. This replaced my 4 & 5" spiral pipe.

There is no difference - the PVC is just better all around. Also - if your going to do it - spend the extra few bux and go 6" - it will make a world of difference.

[JGS]

Snip

"They found that the increased turbulence reduced velocity and hurt transport."

Right > W Canaday wrote:

[W Canaday]

How? The impellers can only move 'x' amount of air in a given time. This is a volume measurement. A larger pipe 'consumes' more of that volume per linear unit and this would reduce velocity all by itself. But there would seem to be a more important matter ... that of the neck and impeller dimensions. Even if I make the main run 6", I am still constrained by that, aren't I?

Or am I?

Bill

[DonkeyHody]

W Canaday wrote: spend the extra few bux and go 6" - it will make a world

Bill, you are making some incorrect assumptions. You are assuming that the impeller is moving all the air it can move, but that's almost never true. Friction of the air moving against the walls of the pipe slows down the air so that the impeller is spinning its wheels so to speak. But you are right that it is possible to size your pipe so large that the velocity falls so low that the heavier chips fall out and aren't moved.

The air can speed up to pass through short sections of a smaller diameter pipe like the throat of the DC.. But if forced to travel through long sections of that same smaller diameter pipe, the friction losses against the sides of the pipe rob precious static pressure. And with vacuum systems, we only have a little static pressure to work with, so it's important not to throw it away.

Follow this link to Bill Pentz's place. I don't buy quite everything he says about the grave danger of airborn dust, but he certainly seems to understand and communicate the science (art?) of collecting dust.

[W Canaday]

Thanks for the good link. I'll try to wrap my grey cells around it this weekend.

Bill