Straight pipe run at inlet

K

KelbyVP

New member
Bill Pentz recommends at least 4' of straight pipe leading to the cyclone inlet. For various reasons, that would require a major re-design of my shop. I currently have the square transition inlet connected to about 6" of rubber hose and then leading to a 6" wye. Even counting the inlet, that's only about 18" of straightness before things hit the cyclone.

Can someone give me a sense of how much of a difference it would make if I could re-design things to have a full 4' of straight pipe? Pentz says the straight pipe will reduce turbulence and enhance efficiency and separation, but that doesn't give me much of a sense of how much difference it would actually make. Like I say, coming up with a re-design that allows for 4' of straight pipe would be a very tall order. So I'm not inclined to bother unless it would make a huge difference.

BTW, my system is not yet operational. Getting this thing up and running has been a very large task. I'm excited to have it, but frankly, it's kept my shop out of commission for three months.
 
KelbyVP,

I cannot answer whether or by how much performance may be compromised with a short straight run into the cyclone body. Perhaps Clear Vue technical support could provide that answer.

I measured the distance from the end of the cyclone inlet to the cyclone body and found it to be about 16” (admittedly a difficult measurement for me since my CV 1800 with a 16” impeller is all boxed in and not accessible). Due to space considerations, I extended the cyclone inlet with a piece of straight 16” long 6” PVC attached to the cyclone inlet for an approximate straight run into the cyclone totaling about 32”. From there I transition to the ceiling with a 45 elbow, a short piece of smooth walled flex hose that is straight and another 45 degree elbow. In that configuration, I have a lot of suction at the drops. But as I said, I cannot say that if I had respected the 4’ inlet rule you cite whether I would get better performance.

As a point of reference, I received the CV1800 in August. It was November, after assembling and sound abating the CV1800 and running duct work to 10 drops, before I got back to woodworking.
 
Ideally we like to see 5’ of pipe coming out of the intake before making any twists or turns. The reasoning behind this is to reduce turbulence - smoothing out the air flow as it enters into the cyclone body. Less turbulence allows for better separation of particles into the collection barrel under the cyclone. It’s not the end of the world if you can’t do it. It just means that you may see slightly more dust exhausted into your filters than you would otherwise.
 
I had to use a 45 degree elbow immediately followed by a 22.5 degree elbow at the cyclone input in order to install my CV1800. There was just no other way to get it installed into my basement shop. I've run it since fall of 2008 and I get very good separation. It probably is not ideal but it works fine for me. I will caution you to get a good seal on the bin because any leak at the bottom of the cyclone will cause poor separation. Make sure every hole in the bin is sealed (like at the handles) and that you have a good gasket at the top. Good luck with your install.
bababrown
 
Thanks, all! I'll make do with the less than ideal turns for now and see how the separation goes. It doesn't sound like the difference in performance would be worth the hassle of completely revamping my shop layout.
 
Agreed. I suspect that even the round-to-rectangular transition piece is a minor source of turbulence. In a perfect (Bill Pentz!) system this piece would be about 4' long rather than the 1-2' the product uses. So given that there's already a source of turbulence close to the cyclone, it's probably not a big additional loss for an elbow to be that close. In practice, the systems do work very well.
 
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There are some design criteria in the Cincinnati Blower engineering manual as well. The CV design suggests that the neutral vane ramp kind of takes care of the inlet turbulence. Having a hard 90 right out the exhaust might benefit from a longer straight run though.

Don
 
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