Long Sweep 90 Elbows for 2729 Pipe Dust Collection

[tvrgeek]

Yes, PVC conduit has wonderful long sweeps, but think in the $500 range! Joints were not designed to be smooth.

 

[Alan in Little Washington]

. . . design the ductwork and that will determine what size (CFM) blower is required.

Mostly correct- but first comes the WW machines- each has its own minimum CFM requirement. That data is available from various sources like Bill Pentz's website, though he didn't originate it (I don't remember the source but it was some professional association). The data also often implies larger dust ports than most hobby WW machines come equipped with. So you'll need to enlarge the ports or adjust the computation.

Then you can design the ducting that will move the CFM needed by the largest machine and/or the one located the farthest from the blower- the worst case. With hobby woodshops where only one machine is in use at a time, there is no need to use step-down ducting like in commercial shops with multiple machines running at a time. Run the same large duct (and flex) from blower to machine. Don't even step down at the drop or blast gate. Also, if you have multiple dromps you will need to put a blast gate at each machine so only one branch/duct is in use at a time. Otherwise, like industrial installations you'll need a ginormous motor/blower. Also, if you sealed all joints properly, have blast gates that seal well,, and don't have leaks, you won't need blast gates where branch ducting joins the main duct (where they can't be reached.)

Unfortunately, you'll be somewhat limited by the diameter of ducting available, especially in PVC- for anything but a tiny shop you will need to use 6" duct. (I won't go into the math, but 4" duct won't permit the CFM needed for anything but the smallest machine. You can get larger diameter duct in metal, but at a really high price. Don't forget to add the SP generated by all elbows, fittings, diameter and length of ductwork, etc. and don't forget the cyclone and filter(s) if using them, when you add up everything to compute CFM needed.

Only then you can select a motor/blower unit. Unfortunately, somewhere along the way, reality and the size of your wallet strike. Then you do the best you can do. If at all possible, the best approach is to vent outside with no cyclone and no filter(s). Hobby woodworkers are about the only folks who attempt to recycle dust collection air. Even with their huge cyclones and bag houses, commercial shops do not try to do that. It is too expensive and puts too much restriction on CFM. Remember a dust collector is a "system" it doesn't matter where the cyclone or filters are located. They can be in front of the blower or after it, but they still add resistance and increase SP.

 

[Charlie]

Alan, Obviously it must be known what machines are being connected and what CFM is required for each.
That is part of "design the ductwork and that will determine what size (CFM) blower is required".
If not, it would be like going to an auto parts store and asking for a starter without stating make/model.
I have a copy of Industrial Ventilation (1982 edition when I took a class at Wisconsin Univ. It shows CFM requirements for most any equipment, wood, metal, steel mills, sawmills, etc. It also shows duct work design, hood design, etc. I'm sure Bill Pentz got all or a lot of his info from it or similar books. He sure didn't learn it on his own. It has required many hours of testing for many years to come up with proper designs. Air tunnels, smoke bombs, etc.
All I am trying to point out is that a blower of inadequate size will not ever perform properly regardless of what you do with ductwork. If a system is right at the point of working/not working, then CFM, SP, friction loss, elbow design, etc. may help. But in most cases a larger blower will solve the problem. As they say you can't put 10 gallons off ????? into a 5 gallon bucket.
You are correct to state that: "the best approach is to vent outside with no cyclone and no filter(s)".
Filters that do any good will reduce CFM by 25-30% or more. I have been venting outside for 30 years and have no filters to clean.
The worry about loosing conditioned shop air is a big myth since I am not in sub zero temps.
For anyone that has a system not working properly, tack off the filter, bag temporarily and you will see a big improvement.
The filters on industrials are not there as a filter. They let dust cake up on the fabric and the dust cake is the filter. Unfortunately too much cake will reduce air flow. Large dust collectors usually have reverse jet air flow to remove some dust and keep the delta P @ 3.3-5. But, it takes compressed air. The system that I spoke of required 45 CFM @ 90 PSI. That is expensive. This all controlled by a photohelic or magnehelic gauge.

I quit. Lol.

 

[Alan in Little Washington]

I can't disagree with anything you've said.

I just wanted to make sure folks knew about the machine issue. It is too often ignored, overlooked or intentionally avoided because few want to modify their machines by enlarging the dust port or adding shrouds. One of the worst dust offenders, hardest to rectify, and arguably the most used machine is the tablesaw. There is an incredible amount of info a newbie must absorb and use to decide what he needs, can afford, and the level of safety it provides. It has often been said, the best protection is a good mask. That is too simplistic, however, because it ignores lingering airborne dust and dust on surfaces and clothing, etc.

 

[DSWalker]

What is the difference in D2729 and the green sewer drain pipe? Are the dimensions the same as the d2729 pipes? Internal/external for fittings?

 

[Rushton]

What is the difference in D2729 and the green sewer drain pipe? Are the dimensions the same as the d2729 pipes? Internal/external for fittings?

See Alan's post #16 above for an explanation.

The green pipe is D3034 and has the same outside dimension as the white thin wall D2729. As Alan explains, both will fit in the same SDR 35 fittings, but the green pipe has thicker walls, and thus slightly smaller inside diameter. It's also heavier. So, for dust collection, the white thin wall D2729 pipe is preferred.

 

[McRabbet]

ASTM D2729 sewer and drain pipe has 0.100" wall thickness, while D3034 (aka SDR 35) has a wall thickness of 0.180". Both have an outside diameter of 6.275" and thus either pipe will fit into corresponding female fittings. Commonly, those fittings are marked for both sizes. D2729 has a cross sectional area of 28.99 square inches while D3034 has a cross sectional area of 27.48 square inches if my math is right. Not a huge difference, but the white D2729 is lighter in weight and cheaper to buy as well as more effective for moving air. By comparison, 4" D2729 has only 12.98 square inches of cross sectional area, well under half of the 6" pipes.

As Alan has suggested, larger ports are necessary to avoid having a bottleneck at the machine -- I made 6" ports for my tablesaw and jointer for that very reason (and yes, I have a ClearVue CV1800 as well).

 

[Rwe2156]

I can maybe see the sanders, but a 3HP blower dedicated to a planer? Just how big is the planer? 2HP directly to a table saw is close to 1000CFM! 15HP? This could mislead people so maybe you should state how big your shop is and machines.

For the average and even above average ww'ing shop, a 5HP blower is plenty big enough. If you're very concerned about blast gates, splurge and get automated gates, but don't buy a mega blower just so you can leave all the gates open!!

I think you've got a lot of experience is mega powered system, though.