DC chip vs fine dust collection

[ian maybury]

I've certainly seen the collapse of lightweight ducting reported somewhere Ole (very possibly here), but can't remember the details which anyway may or may not have been the whole story. It does suggest though that care is needed with lightweight ducting.

Ditto on the leakage Mike mentioned. Noticing that the fits on the spiral I used were a bit sloppy I ran the numbers for an average 0.5mm gap x no. of joints. It ran out to something like 30% of the open area - so taping or effective sealing is definitely needed.

On blower inlet and duct sizes. Should it be of interest to get some data points Chris (I can take some amp readings) my system has 160mm dia (6 3/8in) spiral Euro ducting all the way on the suction side, including the sleeve at the entry to the inlet connection to the cyclone.

Apart from the top cylinder being a couple of inches longer to suit the thro' floor installation the cyclone is fabricated from galvanised steel to the dimensions on Bill Pentz's pages. The fan inlet tube is 9in in diameter for an 18in cyclone body diameter, and its entry (the lower end) and the cyclone inlet chute and ramp are positioned relative to each other and to the cone exactly as in Bill's drawing. (the inlet tube that drops down the centre of the cyclone)

The impeller and blower housing are Clear Vue 16in CV Max.

The blower outlet is 8in (I used a modified transition that attaches directly to the body - see pic below), and it connects straight to an 8in dia x approx 3ft long attenuator before taking a (2 x 45) 90 deg bend to drop about 2ft into the filter cabinet. The outlet from the cabinet is also a full 8in diameter through a 90 deg bend. The filters are 2x Donaldson nanofibre/HEPA cartridges. The option is also there to vent to the outside through an 8in leg that runs about 3ft further on past the bend. This means that my example is 8in or larger right from the blower inlet to the exhaust.

On the suction side the 160mm ducting is full bore all the way too - from and including the flexibles to the end of cyclone spiral. The cyclone inlet chute and spiral have about 9x4 = 36sq in of open area - a bit bigger than 6in duct, but smaller than 8in. The distance and number of bends is a bit dependent on which drop is in use. The shortest run is about 30ft, and has about four 45 deg bends in it. The longest is about 45ft with about 6 bends.

Despite the largish exhaust and lack of restriction in the blower my system still seems to run a bit restricted - even with the drops not connected to a possibly restrictive machine hood. I didn't record the figure, but think it's drawing around 4HP with one blast gate open.

I wonder is it possible that turbulence/inefficiencies in the blower or the cyclone (a cyclone is in one way a device that uses energy contained in the airflow to separate dust - so by definition it's restrictive) could be a restricting factor too? (as well as duct/inlet/exhaust sizes) My blower has the silencing strip screwed to the outer housing just before the exhaust which is supposedly some sort of attenuator -maybe it restricts the flow a bit.

ian

blower exhaust transition.jpgblower assembled on cyclone.jpg