Couplings allow you to connect pipe or fittings together without crimping. The coupling on the left in the drawing is a large-end coupling—it’s designed to connect fittings to fittings. The coupling on the right in the drawing is a small-end coupling, and the ends will slip inside the ends of your pipe. They’re used for connecting pipe to pipe, or pipe to flexible hose. They’re readily available in diameters ranging from 3" to 12".
The two main types of elbows you’ll use in your system are fixed and adjustable. Die-stamped fixed elbows (top elbows in the drawing) offer a smooth, obstruction-free interior. Although gored fixed elbows (bottom elbows in drawing) don’t have as smooth an interior as die-stamped, they still are obstruction-free inside and cost about 20% to 30% less. For odd angles, nothing beats an adjustable-angle elbow—just make sure the radius is at least 1-1/2 times the diameter of the pipe and that it’s made of at least 24-gauge metal.
There are two basic options you can choose from when you need to change pipe diameter. One option is to use a reducer like the one shown here. Reducers are available in sizes ranging from 3"-to-2" up to 10"-to-9", in 1" increments. Go with a spun reducer instead of a welded one, as it has a smoother interior. Another reducer option is to use a fitting called a tee-on-taper. They’re similar in appearance to the tees shown on page 51 except that the one or more openings can be tapered. This creates less static pressure than using a tee and a reducer.
Just like elbows, tees are available in many shapes and sizes. To minimize turbulence and reduce the chance of dust and chips settling in your ductwork, whenever possible you should use tees whose branches enter the main line at 45 degrees. The tee at the left in the drawing is a 4"-on-12" tee, referred to as a "four on twelve” since the branch line is 4"in diameter and the main is 12”. The tee on the right in the drawing is a 6"-on-6". Both are 45-degree lateral tees. Sizes range from 3"-on-3” up to 18"-on-18".
A wye branch allows you to split a branch line equally in two directions. Sizes start at 3”x3”x3” and go up to 10"X10"X10". The opening sizes can vary, such as 8"x4"x4" for situations where you want to split a large main line into two smaller branches. Economy wyes are often spot-welded together; industrial wyes have a continuous weld at each seam. The only drawback to these fittings is that they’re expensive: Prices ranges from $60 for a small wye to $140 for larger sizes.
A swivel-ball joint is designed to connect a pipe to pipe or pipe to flexible hose while allowing it to pivot. Although they’re used primarily in industry to connect to dust or fume hoods that need to be repositioned frequently, they’re also useful for hooking up rigid pipe to a stationary tool where the dust hood moves (such as a small planer). Sizes available range from 4" to 12", and they cost anywhere from - $90 to $250.
HVAC transitions like the round-to-rectangular shown here are quite handy for shop-made pick-ups or dust hoods. They’re particularly well suited for placement behind radial arm saws and power miter saws as dust catchers. Attach the end of a flexible hose to one of these, and you can press it into service as a pick-up for a lathe or even as a simple bench- top or drill press dust catcher.
In the last year or so I’ve noticed a proliferation of manufactured accessories for dust collectors. One accessory package that I’ve found very useful in the shop is a flexible hose with various nozzles like those shown in the drawing. The flexible hose is both articulated and fairly rigid so that you can position it where you want it and it’ll stay there. This setup works great as a pinpoint dust catcher for a band saw, scroll saw, or drill press.
Although most folks think of a floor sweep as a great way to clean up the shop (and it is), you can also use one next to a machine where sufficient dust collection can be difficult (such as a drill press). Floor sweeps are available with or without a door. Both types of floor sweeps need a blast gate above them to control the flow of air; don’t count on the door of a floor sweep for a seal—the amount of air that can slip past one of these can seriously degrade your system’s performance.
Blast gates are used to control the airflow within a whole-shop dust collection system. There are three main types of blast gates available: full blast gates, half gates, and self-cleaning gates. Full blast gates (see below) are the most common and come in sizes ranging from 3’ in diameter all the way up to 24" in diameter. Although blast gates are most often used to control the air flowing to a machine, they can also be used to balance the air going from one branch to another.
You can install half gates in existing ductwork with out having to disassemble the ducting. You cut a slot halfway through the duct and slide the half gate into place. The blade of the half gate is cut round to match the diameter of the ducting. The gate is held in place with blind rivets inserted though the casting and into the existing ductwork. Half gates cost about the same as full blast gates and come in sizes from 3" to 16".
Full blast gates
Full blast gates are available in either metal (usually cast aluminum to keep weight down) or plastic. As always, I recommend using the metal gates, as they wont interrupt the ground path in your system (if connected properly) and they’ll stand up better to wear and tear. Metal blast gates usually have a screw that you can tighten to lock the gate open or closed. To allow airflow to pull the blade tight to the surface of the casting, install the gate so that the screw is pointing in the direction of airflow.
Self-cleaning blast gates are particularly useful in shops that machine either green wood or highly resinous woods that tend to stick to and clog up a gate. On a self-cleaning blast gate, the shutoff blade is longer, and there's a T-shaped rubber gasket on the end of the gate (near right photo). To clean the gate, loosen the two nuts near the gasket so that you can pull out the gasket. Then push the extra-long blade completely through the casting to clear out the chunk.
This article is excerpted from Controlling Dust In The Workshop by Rick Peters.