150mm round pipe?

[Deadeye]

My dust extractor has a 6" inlet.
Currently it's stepped straight down to 4" and then I have Manrose ducting off to machines (almost all 4" ports), via a home made cyclone (also 4" in and out). The runs are longer than I'd like, but the space is a bit convoluted. The cyclone works extremely well (I haven't had to empty the 1um cartridge bags yet) but I'm losing a lot of flow at the machine and the thicknesser, for example, chokes quite easily (it's supplied through about 5m of corrugated flexible tube).

I was toying with redoing everything in 6" and then stepping down at the machine/s. Main drawback is I'd have to build another (bigger) cyclone and 6" round pipe seem fiendishly expensive. Question 1: is there a less expensive source of 6" duct?

An alternative is to put an adaptor in for 6" round to 220x90 rectangular, and then back at the far end. Stupid? Cheaper?

The line-of-least resistance is to leave it be and tweak what I have. If I put in more smooth wall, rigid tube instead of flexible, is that likely to make a significant difference? What else should I try to tweak?

Thanks for the advice

 

[Yojevol]

You say you're losing flow at the machines which is causing them to block up. Does that mean air is being drawn in elsewhere from the machine in use? Do you have blast gates on all machines?
Brian

 

[johna.clements]

I know nothing about the design of dust extraction systems but have studied hydraulics back in the 80s.

The flow will be determined by the roughness of the pipe, its size and shape, and bends and junctions.

Corrugated pipe is rough on the inside so will set up eddies slowing down the flow.

A bigger pipe has less inside surface resisting airflow compared to its area. Round pipes are best, rectangular pipes have a bigger surface area applying friction to resist the flow. 6" round to 220x90 rectangular have a similar cross section (within 10%) but the rectangular section has about 30% more internal surface to resist the flow.

Bends, junctions, changes of section and other fittings all produce eddies which slow the flow.

 

[Doug B]

You could try running 6” pipe from the extractor to the cyclone then reducing down from the cyclone to the machines that’s what I’ve done as from what I’ve read its common to have a cyclone set up this way with smaller pipework on the inlet side of the cyclone.

 

[Deadeye]

You say you're losing flow at the machines which is causing them to block up. Does that mean air is being drawn in elsewhere from the machine in use? Do you have blast gates on all machines?
Brian

I do have blast gates and I think it's all quite well sealed. But the runs are longish and the pipe corrugated...

 

[Inspector]

6"/150mm has triple the flow of 4"/100mm so upping the ducting and removing as much flex as practical will make a big difference. If you can also make a machine's intake 6" as well and open the the cabinet to allow more air in to replace what goes out they will work better too. harder on some machines than others.

Just made a long post in another thread on square/rectangular ducting. I'm not going to repeat it so here is a link to it. #3 The info on equivalent sizing is a link in the first link.

Pete

 

[whereistheceilidh]

6"/150mm has triple the flow of 4"/100mm so upping the ducting and removing as much flex as practical will make a big difference. If you can also make a machine's intake 6" as well and open the the cabinet to allow more air in to replace what goes out they will work better too. harder on some machines than others.

Just made a long post in another thread on square/rectangular ducting. I'm not going to repeat it so here is a link to it. #3 The info on equivalent sizing is a link in the first link.

Pete

This will only be true if the 'sucker' is capable of shifting that much air. A larger bore pipe may be less efficient at shifting the debris than a smaller bore ....but then there is obvoiusly too small. I find that 100mm works fine for my machine ...even from a thicknesser. I have tried a bigger bore size but the pressure drop is not sufficient to shift all the bits when lots of debris is being created.

 

[Inspector]

This will only be true if the 'sucker' is capable of shifting that much air. A larger bore pipe may be less efficient at shifting the debris than a smaller bore ....but then there is obvoiusly too small. I find that 100mm works fine for my machine ...even from a thicknesser. I have tried a bigger bore size but the pressure drop is not sufficient to shift all the bits when lots of debris is being created.

No argument here but the first post said his DC has a 6" inlet which one has to presume can handle the flow from bigger ducts.

The goals of the woodworker also need to be understood. Type and amount of woodworking, budget, shop size, keeping visible the stuff off the floor, capturing the sub micron dust at the source, sensitivity to dust, etc. If you have a sensitivity to fine dust and want to capture it as the machine makes it, you go with big bore ducting and open the machine to accept it without stepping down, or wear a mask for all the dust generating work and for hours after until it has settled out of the air. Many people are not bothered much by dust so a basic setup suits them. Others and I am among them, feel the effects of fine dust during and for a few days after and will need to do more.

Pete

 

[Ozi]

Going to a smooth wall makes a greater difference than you might expect as what you are extracting is not a perfect gas but "gas with lumps in", any corrugation gives chips a point to lodge and initiate a blockage, where possible minimizing the height you try to lift anything you extract can also have a significant benefit, the temptation is always to run along the ceiling but staying at the height of the machine and running slightly down hill is better if practical.

I have just been working on the ventilation system for a mushroom shed and was horrified at the cost of 6" pipe, went for two sets of 4" massive difference in cost

as compared with 110mm £38.60 for 6m before trade discount to make a fair comparison