Dust collector woes

Air velocity is too low

Dick Coers

I don't know what collector you have, and can't tell if you have blast gates at all drops. That 3 into 1 adapter looks like a horrible air restriction though.

Re: Air velocity is too low

John C Lucas

I have a.2400.cfm double bag grizzly. That manifold is at the end of the line and used very seldom. There is a drill.press after that with a 4" hose and it works fine. Its the 6" horizontal run at the other end of the line where thre problem is.

Re: Air velocity is too low

Dick Coers

You can't just blame the 6" line. That's where the dust is dropping out, but downstream issues can be causing the loss of air velocity and flow.

Also those pivot style elbows are bad

Dick Coers

Those furnace duct elbows really rob the system, just like too much flexible hose. Too tight of bend, and every seam in the elbow leaks. If you have to use them, open them up a little so the bend can be less than 90 degrees. Also tape or plastic wrap every seam.

Re: Air velocity is too low

John C Lucas

I have a.2400.cfm double bag grizzly. That manifold is at the end of the line and used very seldom. There is a drill.press after that with a 4" hose and it works fine. Its the 6" horizontal run at the other end of the line where thre problem is.

Re: Air velocity is too low

Barry Irby

The velocity through the duct is related to cross section area. Since the ares of the 6" duct is more than twice that of a 4" duct, the velocity of the air will drop to less than half as it enters the larger duct. Velocity of the air must have enough energy to keep the particles flying.

It's unlikely your DC actually moves 2400 cfm, with the possible exception of if you disconnect the ducts and run the machine naked. As you are aware just about everything about the system restricts the air flow, more or less.

I have a 1100 CFM system and it does well in my tiny shop with 6" mains and 4" drops (plastic SD pipe.) With one gate and sometimes two open. My runs are significantly shorter than yours but nearly as complicated.

Its very difficult for any DC to suck enough air through a single gate on a four inch drop to service a 6" main. Particles in motion tend to stay in motion. Particles at rest tend to stay at rest. (Physics). It's easier to keep them moving than to get them moving after they drop out. I think what you need to do is to open a second gate to allow copious air flow through the main.

Re: Air velocity is too low

John C Lucas

Thats sort of what i just did. I put a.second hose on the lathe so their will be two areas near my turning to pull dust.

Suggestion

Mark Mandell - Gone Round In New Jersey

Rotate your wyes 90° so that the two branches are horizontal (if not tilted up slightly). Yes, that will move either your main or your down line away from the wall but what you have now is a "drop box" for the debris stream running from further down the line. Your blower can't pull the dust across the gap formed by the wye's leg pointing down so the dust drops in to the downlines.

Re: Air velocity is too low

Barry Irby

Just be sure the second line goes directly to the main and not through the same 4" drop.

Re: Dust collector woes

Earl

John did you start your dust collector with that one six line open? That should tell you if its an air flow problem.

Re: Dust collector woes

Don Stephan

Won't the entire system be limited as to air flow by the 4" corrugated flex hose? I ran smooth metal 6" the entire system, and even changed the exhaust ports on my jointer and table saw from 4" to 6". I only used long bends, again to minimize friction against the air flow.

Upgrade lathe drop to 6"

ian neuhaus

even two 4" hoses can't carry enough air to allow a 6" main to flow at optimum. The pipe diameter/air flow relationship is only roughly related to the area of the pipe.

Can you change your main lathe pickup to 6"?

Re: Dust collector woes

Don Evans

What you did depends of what size your collector is. Doing what you did COULD, depending on the manlyness of the collector slow your air movement at the machines.

A good piping system on any collector starts out with the finest dust producing machines furtherest from the collector. Largest dust particle producing machines, like a planer, closest to the collector. The piping main starts out smallest the further from the collector and increases in size the closer to the collect it gets. I have seen this conversation go on groups like this and most say put in 6" main. That just isn't the way it should be done.

My system does have a 6" main part way but 10' from collect increases to 8" pipe to start slowing the air flow so good separation takes place inside the collector (it's a cyclone, Onieda). The system works extremely well.

Don

Don

Re: Upgrade lathe drop to 6"

Don Evans

Increasing this pipe will slow the air more, his problem is the opposite.

Re: Dust collector woes

Don Evans

John:

As has been sayed your problem is air flow is too slow in that pipe.

The wye's that you are using is probably a big part of the problem, the one's you have are design to move air differently than you need too.

They are creating a lot of tubulance at that point in the system.

Also, I would not rely to heavy on the rating of the collector. As you know they bags get clogged with time and can cut down the cfm drasticly.

Your problem is, as has been said, the air is flowing to slowly inside that pipe. The only way to fix that is to correct that problem, to do that, it appears to me, is fix the piping problems.

See my other message for piping recommendations.

Don

Re: Dust collector woes

Don Evans

Wish I could type a message without all the typo's and saying "what" when I mean something else. That for then and things like that.

My excuse is I type words NOT individual letters and the biggest excuse is I don't proofread!

So there, it's a curse to type 45 to 80 wpm.

Don

The guide to ducting  *LINK*


http://billpentz.com/woodworking/cyclone/ducting.cfm

Re: Also those pivot style elbows are bad

Barry Irby

Dick is right about the elbows. Punch a pin hole in the side of a drinking straw and try sucking liquid up through it. It's amazing how a tiny hole can ruin the function of a straw.

You want the air to enter the system beyond the dust and help push it through. Any air that enters along the way ahead of the dust hinders it.

You can coat the seams with duct sealing compound (goop like thin caulking) but that would be fairly permanent. If you use aluminum tape, its hard to remove, but you can slice the seams easily to reposition the fittings and change the angles.

Re: The guide to ducting

john lucas

Here is what I have now. The build up was in the first two sections from the end of the line. I usually only had the very end drop open when turning. Now what I plan to do is have 2 drops going to the lathe. Mostly because I think it will pick up more of the dust and maybe a few more shavings. I need flexible hose because both of them will need to be moved depending on the size of the project. I put A T at the end and put a cap on it so if necessary I can remove it to clean it out, or one time I got a big rag sucked in and had a hard time getting it to go all the way to the dust collector which has a safety grid to keep things from going into the fan. It's also easier to disconnect that end.

Re: Dust collector woes *LINK*

Hank Knight

"Won't the entire system be limited as to air flow by the 4" corrugated flex hose?"

Not necessarily. When the flow of a fluid (a gas or a liquid) passes through a restriction, the pressure drops and the flow increases to allow the volume of the fluid to pass through the restriction. It's called the "venturi "effect"(http://sciphile.org/lessons/bernoullis-principle-and-venturi-tube). It's what makes an airplane wing lift an airplane and it turns compressed air flow into a vacuum. Corrugated flex hose is a different issue, and the corrugations do, indeed, limit the air flow in a DC system, bit the limitation is due to the corrugations, not the decreased diameter of the hose.


Bernoulli's Principle and the Venturi Tube

4" stretch plastic wrap

Dick Coers

Just a couple wraps with the packing stretch wrap works great. It's so thin that if there is a leak, the vacuum pulls it to the leak and seals it. Very easy to remove.

HVAC fittings are just not that great for dust

Dick Coers

Your system looks nice, but in my opinion, not great for dust and chips. Short radius sweeps, and 90 degree Ts just rob air flow. Your drop out of chips and dust prove it.

Re: The guide to ducting

Bill Tindall, E.Tn.

As others have said the problem is insufficient air flow either because the blower is not capable of moving enough air or too much pipe resistance.

That mile of corrugated pipe could be the problem. Why didn't you run the header to where the lathe is and just do a short drop?

I attended a dust collection seminar given by an expert in the field and he showed the huge friction losses this pipe generates. It creates turbulent flow and that is bad news for moving air. You can do an easy test. Accumulate the layer of chips and then disconnect one or both lengths of that pipe. If the chips don't fly down the pipe then the problem is with the blower or filter bag.

I have a 1.5 HP Oneida system with 7" runs and smooth 5" flex pick ups. I accidently sucked a bench brush off the bench and it went down the pipe. I have to be careful to not get anything that fits in the pipe near the end of it.

I presume when you are using the lathe that the other outlets are gated shut?

I envy all those windows.

Re: 4" stretch plastic wrap. Good idea