where is the rub?

[Bruce Seidner]

Ok, sharp angles like 90deg rights or T joints rob you blind of CFM.

But where is the rub?

I need to construct a connector that is limited in height but not in other dimensions. I have a very low ceiling, a traditional cyclone with a top discharge and a blower that has to be mounted horizontally, at right angle to the cyclone. A tall 90 degree bend will not fit.

So, while it would be problematic to have a short curve right angle with my cylcone's 7" discharge duct, what would happen if this were opened up such that it was a larger duct that connected the discharge from the top of a cyclone to the intake of a blower.

Can you mitigate the friction of the right angle by increasing the size of the port diameter or changing the shape of the port? I can think of lots of ways to fashion a connector but don't understand the physics or the issues that would inform the efficacy of the 90 degree bend I need to make that is limited only by the height above the cyclone. There is room for about anything else around or below it.

Ideas are welcome and invited.

[Dan Hintz]

Can you mitigate the friction of the right angle by increasing the size of the port diameter or changing the shape of the port?

Yes... but it won't be a straightforward exercise and will involve a lot of trial and error to get it the best it can be. Too wide of a port offers no advantage as you have to neck back down again. To sharp of a turn and you've beaten back the advantage of a wider port.

I would suggest looking at ways to modify the blower setup, not just the tubing. For example, I moved my motor from sitting on the base/floor to up on a wooden pedestal, rotated 90 degree and aiming directly into the cyclone ring. This shortened the path a few feet and removed two 90 degree angles in the path. I posted pics within the last few months, so do a search on it.

[Anthony Whitesell]

Would another way to ask the question be:

If the cyclone inlet is 7" and the main trunk is 6" then are these losses the same:

A) 7" elbow connected to 6" duct

or

B) 6" elbow connected to a 6" duct

Remembering that the CFM is the same, as restricted by the 6" duct.

As an engineer, my gut tells me there less losses in the 7" elbow flowing at the CFM of 6" duct would be less than that of the 6" elbow.

[Chris Friesen]

I have a very low ceiling, a traditional cyclone with a top discharge and a blower that has to be mounted horizontally, at right angle to the cyclone. A tall 90 degree bend will not fit.

Any chance you can go up through the ceiling?

[ian maybury]

My installation goes through the ceiling.

This question of connecting a remote blower surfaced only a few days ago, but wasn't definitively answered.

I've a background in modifying exhausts, and when I see a short pipe like a blower inlet am immediately inclined to think in terms of tuned lengths - pressure waves and the like reflecting from the ends of the tube.

One major distinguishing factor in cyclone performance is the ability (or not) to drop out very fine dust. Some apparently do this pretty well, but i've no idea what the pattern of airflow in the bottom of the cyclone cone that delivers this may be. (my cyclone is a DIY in galvanised steel, maybe some of you guys have seen more with a clear plastic CV model)

There's a strongly circulating pattern to the flow visible right down into the hose linking the cyclone to the chip drum on mine. The interesting part though is exactly how a top performing cyclone gets what is very very light dust to drop into the drum - even the slightest airflow in the wrong direction could stop this happening. There's meanwhile a pretty spectacular amount of air moving through the cyclone - so it wouldn't take a great deal by way of the wrong sort of turbulence to cause a problem.

It seems quite likely that whatever the effect is it could be quite dependent on the precise dimensions of the cyclone outlet, connection hose and drum inlet area. Against that, this might not be the case at all.

This is why I'm inclined to be quite cautious. Viewed from a solely pressure drop/air flow perspective the use of some sort of duct to the connect the blower to the cyclone probably isn't a problem. It might be another deal though if the result is to in some way significantly disrupt the required airflow.

It'd be interesting to know if there's been any computer modeling of this done.....

ian