what size ducting should I be using? 20 inch impeller, 4kw machine

[Albert Lee]

looked through at least 5 pages of relevant pages, couldnt find the info I need.

I have a baghouse unit, the advertised figures of the extractor are as below:

Volume: 5440 m3/hr, 3200cfm (I think this is taken with no static pressure and no bags connected, naked value if you know what I mean)
Speed: 35 m/s, 6800fpm
inlet size: 250mm, 10"
Impeller size: 510mm, 20inch
motor kw: 4kw 3phase at 410v

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the longest ducting will be under 20feet.

it will service a 37" sander and a combination machine.

following Bill Pentz comment, if I use smaller Ducting, the speed will rise but I may suffocate the extactor because not enough air. if too large, then there wont be enough air speed.

I feel 6" maybe on the small side, and 10" maybe too large? will I be suffocating the extractor with 8" duct? keep in mind the impeller is 20inch....

thank you for your time

[David Kumm]

Albert, you won't know the answer without looking at the type of impeller. 20" is large for a 4kw motor so the design must be different than what we usually see. I've seen impellers that look a little move like a squirrel cage type design. They tend to be larger diameter and move a lot of air under low pressure but don't deal as well with resistance. Michael will know way more. I would be careful putting too much restriction on an impeller unless I knew it could perform under pressure. 8" vs 10" might not matter at 20 ft but you should find out from the manufacturer or at least look at the Cincinnati Fan tables and find an impeller that looks close and see how it performs. That will at least give you a clue. Dave

[Michael W. Clark]

Hi Albert,
Dave has a good suggestion in trying to find out the wheel type. It may be a backward incline if on the clean side of the collector. Most fans after a cyclone or in hobby single stage units are radial blade (paddle wheel) type.

[Albert Lee]

Thanks for that David, I will have a look on the Cincinnati website and upload a photo of the impeller later today.

[Albert Lee]

I have checked the Cincinnati website and checked my impeller, I think it is an open paddle wheel.

[Michael W. Clark]

Hi Albert, look at the RBE-11 on the Cincinnati Fan site. Is this belt drive or direct drive? What is the fan speed (RPM)? You want to look at values in the table for your fan RPM. This will give you an idea of the flow vs. SP relationship. I suspect the 3200 CFM is as you say, a minimal pressure requirement condition.

Mike

[Albert Lee]

Hi Mike

thanks for the input, the motor is a 4 pole, direct drive, 1725rpm, will have a look at the rbe11

[Albert Lee]

I had a look just now, for direct drive, 1750rpm, 4" sp, the motor is 2624cfm/3.5 bhp, what does this mean? My motor is 5hp, it's higher than the 3.5bhp (ok the hp and bhp not exactly the same in theory)

[David Kumm]

Albert, if that is what it is, and it does look similar, you won't find it effective for dust collection. I run an RBE 9 at 3500 rpm and it is a high pressure blower relative to backward curved impellers but at slow speeds it won't move enough air under pressure to work with even a 10" main. You need a higher rpm motor and a vfd to balance it out. The straight blade impeller pulls at pressure but takes more HP. My RBE 9 is a 15.75 x 6.25" radial and I run 8" pipe with a 7.5" motor. Increasing the blower to 20" increases the HP demand greatly as you can see on the tables . if run at higher rpm which is necessary to acheive cfm under the normal 10-14" of static pressure, you are likely to need an even larger motor. Dave

[Michael W. Clark]

Dave,
If he is not running a cyclone and has short duct runs, he may not need as much SP as you do with your Torit cyclone. If he can do 1500 CFM in an 8", should be good for that sander based on comments from the other thread, correct? The BH is fine with a lower flow, actually works better.

I would check the safe speed on the fan before speeding it up. Any nameplate info on the fan?

[Thomas Canfield]

I checked and the standard voltage in NZ is 230V 50 Hz. The 50 HZ will reduce the motor speed by 50/60 compared to the 60 Hz in the USA. It makes a big difference in the performance of centrifugal equipment. You really need to find a performance curve for the fan at the correct speed to see how it will perform. So far the data listed looks like a mix of information. In my engineering past, the 50 Hz always required going to larger equipment to get the required flow and pressure while piping was same for the same process system.

[Albert Lee]

Dave,
If he is not running a cyclone and has short duct runs, he may not need as much SP as you do with your Torit. If he can do 1500 CFM in an 8", should be good for that sander based on comments from the other thread, correct? The BH is fine with a lower flow, actually works better.

I would check the safe speed on the fan before speeding it up. Any nameplate info on the fan?

yes I am not using cyclone and the longest duct run is only 20 feet (vertical + horizontal).

as for the name plate on the fan, the baghouse extractor a Holytek DC006, made in Taiwan, I dont think they have any market presence in the US. anyhow below is the screenprint of the brochure, the air volume figure didnt make sense, 155m3 per second?? 2nd pic below is from another website, the volume is 5440 cfm, probably m3/hr which makes more sense...

Again thank you for your time!



SKMBT_C28014040213450.jpg
holytek.jpg

[Albert Lee]

yes thats right, its 230v here for single phase.

[David Kumm]

You are probably correct, Michael. The fines need less help so it might be made to work. I'd think about enlarging the port to match the pipe size. Even 20' of 8" with a couple of ells and a smaller port might be on the edge. Not restricting the port would help. I'm assuming the motor rpm is at whatever hz is used in the country so 1750 is what the impeller would run at. You won't speed it up much without a larger motor but at least the Cincinnati impellers are the same for 1750 and 3500. I think the 20" is rated at 4000 but that would sound like a jet engine from the inside. Dave