Piping for dust collectors
In this article we point out the differences in metal ducting that is available and show you what is acceptable and what is not.
While HVAC (Heating Ventilating and Air Conditioning) adjustable elbows and snap-lock piping are acceptable for “homeowner” installations, you must be sure to use the proper gauge piping.
HVAC piping and fittings.
Recently, I had a woodworker call me concerning the piping in his shop (re: the gauge of the piping needed and a source for the piping). He has two 3Hp collectors in his shop (one at each end – both having their own piping systems). He had gone to his local hardware store and picked up 5-foot lengths of ducting and piped his systems. However, when he started the first collector up he collapsed 30 feet of the piping. The reason: the 5-foot lengths are basically perimeter piping and usually only 32 gauge (the higher the gauge number the thinner the metal). HVAC piping is designed primarily to have a pressure inside it and possibly a light vacuum (some return air lines). When you use this piping for dust collection you subject it to a reasonably high vacuum.
Guidelines for installation
• ¾-1Hp systems 28 gauge
• 1 ½ -2Hp systems 26 gauge
• 3Hp systems 24 gauge
• Over 3Hp spiral seamed pipe
One thing that you need to have on hand for your piping installation is Red Green’s favourite tool: duct tape. You will need to wipe the piping clean (it usually has some oil film on it from the manufacturing process) and apply the duct tape not only at the end joint but also along the seams.
When you use the adjustable 45-degree elbows you will also need to tape all the movable seams in the joint. This will seal against air leaks.
When you are selecting the fittings to use in your system keep in mind that the last thing you want is obstructions that can catch or trap shavings. On most HVAC “Y” type fittings the branch arm is attached to the main body of the fitting using bendable tabs. These tabs stick inside the pipe and are not always tight or flat against the inner surface.
Also the joint between the main body of the fitting and the branch arm is not usually sealed. There are stamped “Y” fittings available but they tend to be constructed of light gauge metal. Your fittings should be made of the same gauge material as the rest of the system. I have a local sheet metal shop build the fittings to my specs (the branches are spot welded in place).
I normally use a good silicone caulking to seal the joint. Also most pre-made fittings that you can buy in the local hardware have at least one crimped end (the small end). A good shop can make the fittings without crimping any of the ends but sizing them to fit together properly.
If your fittings do have crimped ends remember that all these ends should be assembled into the system so that they point towards the dust collector (this is so nothing will become snagged on the joint) NOTE: this is opposite to the rule for HVAC piping.
Piping tips where neatness counts
1. Be sure that all your piping is the correct gauge for the Hp of your collector.
2. After you determine where your main header will run, snap a level chalk line to indicate the center of the pipe. This is a great help with alignment.
3. Be sure to wipe down all the joints and seams before applying duct tape.
4. “Y” branches should only enter the main header from above or the side NEVER BELOW. (The only exception to this rule being if the drop is the last one on the header, then it can come into the bottom of the line). NEVER USE “T” fittings.
5. As uncomfortable as they can be, remember to wear gloves when cutting or handling cut pipe.
