HVAC duct for 10hp dust collector?

[glenn bradley]

I believe they make female to female couplers. That is all that I will need. Nothing on the wye’s need modified to my knowledge. The spiral pipe is all males on both ends. The spiral pipe should mate up to the female end of the HVAC wye’s no problem and for the male end of the wye’s I can use a female to female coupler. Right?

I believe Jim is referring to direction of airflow versus the male/female connection.

[Jim Becker]

I believe Jim is referring to direction of airflow versus the male/female connection.

Correct. HVAC wyes have the crimps on the opposite legs that they would be for DC since air flow is in the opposite direction.

[Carl Beckett]

My first reaction is, wow, that is a big (powerful) DC system! It seems overkill in terms of cost, power consumed, sucking outside air into the shop (unless recirc internally). Unless you are a commercial shop running several large machines at once.

But hey I have done the overkill myself from time to time. Just means short of collapsing your ductwork, pretty much anything will work. To help reinforce the ductwork, instead of wood reinforcement rings I have sometimes used simple band clamps every so many inches. They provide a slightly thicker material right at that point that sometimes is all you need. Alternatively you could take sheet/shim stock and simply wrap it and fasten with a band clamp. That would provide stiffness without it having to be fabricated.

[John Brougher]

My first reaction is, wow, that is a big (powerful) DC system! It seems overkill in terms of cost, power consumed, sucking outside air into the shop (unless recirc internally). Unless you are a commercial shop running several large machines at once.

But hey I have done the overkill myself from time to time. Just means short of collapsing your ductwork, pretty much anything will work. To help reinforce the ductwork, instead of wood reinforcement rings I have sometimes used simple band clamps every so many inches. They provide a slightly thicker material right at that point that sometimes is all you need. Alternatively you could take sheet/shim stock and simply wrap it and fasten with a band clamp. That would provide stiffness without it having to be fabricated.

In the process of extending my 6" HVAC ductwork along 30' of metal wall, I hit upon a "support system" to hang the pipe. I pre-drilled holes 6" apart (vertically) and, using a sheet metal screw with a "built in washer", trapped a length of 16 gauge galvanized wire under each head, making sure that at least every other pipe joint had a support wire across the (already foil-taped) joint. The wires were then twisted together with the twist tightened with a pair of pliers before snipping off the excess. Once the whole run was assembled (Wyes and all), I went back to snug up and level the whole run by twisting the wires that weren't across the joints.

It occurred to me that, given the "pull" against the wall by tightening the wires, there would be a tendency to "egg" the shaped of the duct. To counteract this, I wrapped a single wire one time around the pipe adjacent to the support wire and snugged that tight by twisting the ends together. In order for the pipe to "egg" (or flatten), part of it would have to "spread" and this wire prevents that. If you're concerned with your duct being flattened by the suction, you could put 2 or 3 of these "wire bands" along every 5' section of pipe. 5 or 6 twists would give you all you'd ever likely need to greatly strengthen the pipe. The 16 gauge wire isn't going to stretch.

No guarantees on what kind of implosion you're likely to generate if you close off all of your blast gates and don't use the "open ended main duct" approach, however. There's a video out there somewher showing a railroad tank car being sucked flat by a vacuum trunk when the vents were closed. Pretty impressive. (This was a "controlled test" btw).

[Michael W. Clark]

IF you dent the duct by pulling it against the wall, it will be easier to collapse. As long as you don't dent or crease it, the curved surface will better resist the negative SP.

I think I remember the railroad tanker car referred to and it was on mythbusters. If it's the one I'm thinking about, I think they finally dropped something on the car (a beam?) that dented the shell, then finally got it to collapse. They couldn't get it to collapse otherwise.