Tips for Central Dust Collection

If you’re considering putting a central dust collection system into your shop, I’m going to give you some tips here to keep in mind that are going to make things work a little better, work a little more efficiently, so that when you’ve got a good dust collector pulling air, you’ll get an optimal performance at the tool.  If you’ve got a big inlet on the dust collector, maintain that large diameter for much of the run as you possibly can. The larger that main trunk is the better off you’re going to be. Here’s an example. If you take four inch pipe and compare it to five inch pipe, going just one inch larger in diameter actually gives you about twice the air flow through that system. So you can imagine, if you neck this down from eight to four, the resistance you’re going to be providing to the airflow. So again stay large as long as you possibly can, go small when you’ve got to do drops specifically to a tool.

Now talking about the drops to the tools, that’s where you’re probably going to start working with 4” flex hose. In the perfect world, what I’d like to see is a flex hose that’s got metal coils on the outside of the pipe. The benefit to metal coils on the outside is that I can ground those metal coils so that I’m going to help take static electricity off the system here. What happens is that of course as we’re pulling chips and dust through the plastic, we’re building up a static charge. If I’ve got metal coils on here, I can ground those, and dissipate the static. If you don’t have metal coils, you’re gonna have to take a step to provide a ground in order to dissipate that static charge. What I do like about this pipe is the fact that when I open it up and I put my hand inside, because the coils are on the outside of the plastic, the inside of the pipe of the flex pipe stays pretty smooth. So a test you want to do when you’re buying that pipe is open it up, run your hand inside there, and see how smooth a wall we have. The smoother the wall, the better collection we’re gonna have, because again, you want to stop stuff from impeding airflow. If this is full of ridges, that’s going to impede airflow and it’s going to mess with your efficiency. What you want is double wall flex tube.

Now talking about flex pipe, you want to limit its use. Stay with solid pipe as long as you possibly can. Here’s the number with that. If I take a four foot length flex, a four foot length of solid pipe, this is going to have about three times the resistance to airflow that the solid pipe will have. So again, imagine the loss you’re getting in airflow, or the loss of efficiency at the tool. None of those are things that you want. So limit your use of flex pipe as much as you possibly can.

One option you have is to go to the home center and get standard off the shelf HVAC products. This is fine for dust collection. A general rule of thumb is that, pipe like this is generally recommended for systems using a two horsepower or less dust collector. And the reason for this is it’s relatively thin walled. Usually HVAC pipe off a home center shelf is 24 gauge, 26 gauge, maybe 30 gauge. Remember that with the gauge as the number gets bigger, the thing gets smaller, so 30 gauge wall thickness is less than 24 gauge. The problem you can run into with a large dust collector is that, if it happens that the blast gates all end up closed in the system, and you kick on the dust collector, with a thin wall pipe you can actually collapse the pipe, and you don’t want that to happen. So what do you do in that case? One option is what’s called spiral pipe. Because of the way this is made one, it’s a thicker gauge and two, with its spiral nature it’s virtually impossible to collapse this stuff. So with a larger system, yes it’s more expensive, but spiral pipe is a good consideration.

What about plastic? What about using PVC? So PVC isn’t a bad option at all. You can get it four inch, you can get it six inch, it can satisfy a lot of your dust collection needs. What do we already know that we’ve got to take into account? What about this whole grounding thing? If you use plastic pipe you’re going to have to add grounding to it, which is commonly done by just having a wire lying inside the pipe, that’s then subsequently grounded. That’ll ground the static charge. One of the things I want to point out is, not all PVC fittings lend themselves to dust collection. You might very well say well okay, I’ve got a four inch pipe on the ceiling, then a 4 inch drop. The problem with this is, think of dust coming into the system like cars getting on the freeway. In this case, the cars coming in and has to make a sharp turn. That’s not very efficient. In this case the cars coming in on an on ramp, and can easily merge with the existing traffic. This is what you want. You want merge, not a turn from a stop sign. So using some of the standard PVC fittings is going to limit your efficiency, because you don’t have the gentle onboarding that you get from dust collection fittings. If you do go with PVC, you don’t have to worry about gluing everything together. You can simply screw it together. There is enough friction on those joints so you can screw it together. The benefit to that is, if you ever do get a clog in the system, all you have to do is take out the sheet metal screws, open it up, get the clog out, put it back and you’re back in business again.

Now let’s go back and revisit our HVAC a little bit. You’re probably going to need elbows. As a general rule of thumb you want the radius of this elbow to be twice the diameter of the pipe, so a four inch pipe should have an eight inch radius. We can work around this by joining two elbows that have been formed at forty five degrees. So net we get a 90 degree transition. But look at how much larger we’ve made the radius. So that’s what we need to do in order to make sure that that air keeps moving, and keeps moving efficiently. Now if you go this route, one of the things we don’t have here is a good airtight system because by the nature of the way these babies work we spin them to adjust the angle. I would go back and caulk each of these seams after you’ve got them formed correctly, to make sure that each of those seams correctly sealed. Now while we’ve got this at a 45, let’s go back and look at our main inlet because there’s another thing to consider. A much better move is a 45 out of this, a piece of pipe, a 45 over to get to the horizontal. That’s a smoother transition, again it’s going to keep all your dust flowing better and give you better efficiency in the system.

Similarly then, let’s keep talking about our HVC components. Should we use this one or not?  You already know the answer to this. Is this a right turn or a left turn, or is it a freeway entrance? So a standard T from HVAC systems isn’t something we should use for dust collection. Again we want to provide that on ramp type setup. When you’re stepping down, make sure that your fittings funnel down, as opposed to having a distinct step. That is a much better transition. We want to have an angled transition in between, not a sharp step. With the HVAC components, like I said, be sure that you caulk the seams on those elbows when you’re done. You can use silicone caulk. They do make specific ductwork sealant that’s readily available from a home center, so that you can make sure you’re good and airtight on these parts. Keep those tips in mind so that once you’ve got a good dust collector in your shop, you get an optimal performance out of it at the tools, and making sure you’re getting all the dust collection that you need. And you should get based on the performance of the machine.