Thread: Cyclone upgrade

Originally Posted by rev

About 12 years ago I built a BP cyclone driven by a 12” impeller swung by a 2hp (a Chinese DC blower). I used 6” stormwater pipe ducts with small pieces of flex for awkward small angle bends. I only ever used one machine at a time and all dust ports were opened to the surface area as a 6” circle. The blower inlet was opened to about 165mm diameter which made the motor pull 7.6A, just below its compliance plate rating. It was exhausted into a stack of large truck air filters.]

The cyclone may well have been built to BP design but 2HP motor with 12" impeller will simply not draw enough air to meet BPs other specification of requiring 1000 CFM at the source to make sure enough air is collected to collect fine dust.

Second point - the small amount of dust in the filters could well be confirmation of the previous point (i.e. your system is just not collecting it) and truck filters are not that efficient at collecting dust anyway so chances are the really fine dust was going straight through the filters .

Opening up the dust ports to be equivalent to a 6" area is wasted unless sufficient ari can get into machines. Most machinery is seriously throttled and prevents air from getting into the machine and sweeping away the fine dust. There's not much else's that can be done other than getting out the angle grinder and cutting more openings in cabinets. The classic example is the lower cabinet of most bandsaws. These things benefit considerably by adding a grill covered opening into the lower cabinet. The area of openings for the incoming air to cabinets should at least be double that of the outgoing duct size.

The project was a temporary obsession! But whether it actually achieved what I hoped for (safe fine dust extraction) is uncertain. The filters would collect only a cupful of fine dust from one or two bins of normal waste, but I was still having to vacuum the shop tables etc from time to time for settled dust.]

That confirms confirms all of what I said above

We have recently moved and I need to set things up again. A few days ago I visited Spankingpigeon’s place (a fellow forumite) and saw his Clearvue cyclone in action. That thing really sucks! Now I have cyclone envy and I’m starting to suffer from upgradeitis! The problem is that when it comes to my hobby I have a Champaign taste on a beer budget. ]

Thats because they're using at least a 4HP motor and a 14" impeller.

I now have a 15A 240V supply in the new shed so I’m thinking of using a 3 phase 3.0kw (4hp) motor driving a 15” impeller (via an inverter VFD at 60Hz) for maximum oomph from the blower. Actually it comes from a Flender DC (looks like an old version of a Felder AF22) which was embarrassingly cheap. I found a suitable VFD listed on ebay for around $170.

If the motor is only drawing 8.7A at 240V then its really only generating 3HP - but that is not that important.

Is there any real benefit in using 8” duct with this blower given its impeller size and power? If so, where can I source it (and Y transitions to 6”) at a reasonable price around Adelaide?

8" ducting is useful if more than one machine is going to be used at the same time
OR
you deliberately want to use 2 x 6" ports e.g. on a bandsaw
OR
You want to rapidly vent a shed thereby opening up 2 x 6" ducts at the same time will do this

Getting hold of 8" is a problem. There's no such thing as 8" PVC ducting (not at any sort of reasonable price) so you are forced to use metal ducting or make your own rectangular ducting - this is quite feasible for straight lengths a little tricker to make the bends but not impossible,.

With the bigger blower, am I right to think that the separation of fine dust should be so good that venting it outside rather than into filters would be OK because the amount of expelled fine dust would be negligible? [Remember that my cyclone is built to BP specs for a 2hp blower.

The physical size is critical in getting fine/coarse dust separation so if your cyclone is built to BP specs for a 2HP/12" blower it should be physically smaller than if it was built for a 4HP/14" and it won't work as efficiently just by adding a bigger motor or impeller.

Looking at your thread about this the photo shows what looks like a full size cyclone so maybe you are OK.

Thanks so much for taking the time and making the effort to reply BobL.

Unfortunately I can't lay my hands on the calculations from Bill's spreadsheet that were made when I constructed my cyclone. [I'll visit Bill's site and see if I can work back from the sizes I can measure.] It worked out to 500ml in diameter I think. I was trying to get the most from a 2hp dust collector that I could manage and it certainly functioned better than when it was working with a bag. But you are confirming my suspicion that it was really inadequate.

Now would you suggest building a new blower housing for the 380mm flat blade impeller and 4hp motor combination or just cannibalising the AF22 (cutting off the blower section) and mounting it atop the cyclone? By the way the AF22 blower outlet is a square section of only about 115mm high and wide, which seems to me too small compared to the 140mm circular inlet flange. With a customised inlet could I increase the inlet slightly to say 180mm and make a 200mm outlet so that exhaust resistance is reduced; would that be of any real benefit?

I think I'll dump the idea of 8" duct for the reasons you have outlined and just operate one machine at a time (which is my habit anyway).

An important consideration for me is the potential hazard of expelling fine dust laden air outside of the shed. The risk of a teaspoon or so per full waste bin seems negligible, but a cup full might be significant and cause me to reconsider using a filter.

I was also confused about the 8.7A rating at 240V. This makes it seem like a 2.088kw motor but the plate clearly says it is a 3.0kw unit.

Originally Posted by rev

Now would you suggest building a new blower housing for the 380mm flat blade impeller and 4hp motor combination . . . .

Flat blade means it will be "LOUD" and even "LOUDER" at 60 Hz - this is a major reason why manufacturers avoid uses these.
Last year our local mens shed picked up a free straight bladed DC and I wrote about it here
https://www.woodworkforums.com/f200/school-dc-issues-187759
- there's stuff in this post about noise levels and static pressures that you may find useful

If noise is not an issue then that is fine, otherwise I would suggest you spin it up first and hear what it sounds like before you put any work into it.
Get yourself a smart phone app with an SPL meter function will help quantify things far better than your ears.
At the same time I would measure the static pressure it generates so that you know what you are starting from.

. . . . .or just cannibalising the AF22 (cutting off the blower section) and mounting it atop the cyclone? By the way the AF22 blower outlet is a square section of only about 115mm high and wide, which seems to me too small compared to the 140mm circular inlet flange. With a customised inlet could I increase the inlet slightly to say 180mm and make a 200mm outlet so that exhaust resistance is reduced; would that be of any real benefit?

You can't just put the impeller into the cyclone. It absolutely has to be incorporated into a well designed blower using that mates properly to the cyclone or the cyclone wont work properly

BP has an excellent design for a spiral path blower housing with a 14" impeller on his website - I would follow these instructions as close as possible (especially the inlet and outlet sizes) as this could reduce the static pressure it should be able to generate.

Un-choking the blower can also lead to problems - see below.

An important consideration for me is the potential hazard of expelling fine dust laden air outside of the shed. The risk of a teaspoon or so per full waste bin seems negligible, but a cup full might be significant and cause me to reconsider using a filter.

If it's venting outside, the amount of dust is not that important because if the cyclone is well designed even if it's a bucket of dust you won't see is as it will be invisible and diluted into the atmosphere. It might be possible to see a large amount of dust settling in the vicinity of the exhaust if you have still (i.e. no wind) days while making dust otherwise you should be OK.

I was also confused about the 8.7A rating at 240V. This makes it seem like a 2.088kw motor but the plate clearly says it is a 3.0kw unit.

What this indicates is that that this blower/motor combo was "restricting the motor" and this is not unusual since it protects the motor from overheating. Power use by blowers/motor is counter intuitive - when a blower is restricted it cavitates and ends up moving less air hence doing less work and drawing less current. Freeing up a a blower may move a lot more air hence the motor will draw a lot more current, especially if you go to 60Hz. BTW be vary careful testing an impeller/motor that is not connected to any restrictions like a cyclone or filters as they can draw a lot more current and overheat and damage the motor. A well made and matched VFD will protect a motor and cut out of too much current is drawn for too long.

Ultimately what restricts the flow of air is the static pressure a blower can generate and the diam of the ducting used.
It doesn't matter if a 3, 4 or 5HP motor is used, if their impellers all generate the same amount of pressure - which they usually do, then 6" ducting limits the flow to around 1250 CFM and the requires the same amount of work or the same current irrespective of the motor size.

8.7A is the sort of current that my 3HP DC draws when my filter start to get dirty. When the filters are clean the current is around 9.2A. This is the sort of current the Clearvue draws as well at 50Hz when connected to 6" ducting. It's basically all determined by the ducting

However, these figures are the limit for a 3HP/smaller diameter impeller, using bigger ducting won't generate much more air flow.

What a 4 and 5HP motor and bigger blower can do is move a lot more air if bigger or multiple lines of ducting are used.

Thanks BobL.

Overall then, what upgrade steps do you think would be most beneficial for my system, given the AF22 blower (or parts) that I could now deploy?

As for the noise, it surprises me that a company with the reputation of Felder opted to use the less efficient and more noisy flat vanes on its DC impeller. It would be best to mount it outside for the sake of noise; unfortunately I don't think it would please my neighbours to do so. I might have to look at some isolation inside the shed.

Hi Rev

I have been down a very similar path to you. Built a larger diameter cyclone from Bill Pentz's plans and converted a paddle fan that had a odd shaped body. You can see how I did the fan body at

https://www.woodworkforums.com/showth...ht=fan+follies

I have now installed it and done the ducting

https://www.woodworkforums.com/f200/floor-duct-combination-machine-188719

I was quite concerned about the noise from the paddle fan and so made up a serious muffler. It has been quite effective - details are in the post as are some sound measurements. At this level I can live with the noise but I am on 10 acres.

Mine blows straight outside and I have observed no issues. It is certainly retaining fine dust, there is a deposit of it under the IP lid that I built into the bin and lining on the inside of the bin. I have no way of measuring what it is blowing out or indeed anything else about the system but subjectively it feels a great deal better that where I was before and crucially for me my asthma hasn't flared up.

I will be very interested to hear how you get on.

Regards

Ian

Thanks for your interesting input Ian. I really appreciated the links you included too.

The cyclone I am about to 'upgrade' has a piece of foam carpet underlay sandwiched between the blower casing and the plywood top of the cyclone in an attempt to reduce transmission of vibration and noise to the rest of the structure. I can live with the noise level it makes but it is from only a 12" impeller and 2 hp motor at the moment.

Hi BobL,
I am a bit confused by something you said in an earlier post that has caused me to doubt my understanding of the relationship of blower hp rating to cyclone size. Would you please help me understand what you meant?

I know this might seem counter intuitive, but my understanding is that the horse power rating of the blower needs to be greater to generate cyclonic action when turning the air in a smaller tighter radius, thereby making physically smaller cyclones available to higher powered blowers and requiring larger cyclones for smaller powered blowers. In other words it takes more power to overcome resistance and spin the air stream tightly because its natural tendency is to not change direction. Because I used a 2 hp blower on my initial build I needed a larger cyclone to make it work as well as it could (or at least so I thought).

However you say:
The physical size is critical in getting fine/coarse dust separation so if your cyclone is built to BP specs for a 2HP/12" blower it should be physically smaller than if it was built for a 4HP/14" and it won't work as efficiently just by adding a bigger motor or impeller.

So I understand your comment to be referring to fine dust separation characteristics only, rather than more generally about power to size relationship of the cyclone build per se. If so, no problem (I think!).

BP makes some illuminating remarks re cyclone sizing:
Many have even built these units with oversized cyclones to permit them to use smaller motors. Although I don't particularly like this idea because too much fine dust is not captured if the blower does not move enough air and separation efficiency goes way down, many successfully power my cyclone design with 1.5 hp motors. Instead of building my recommended 18" diameter cyclone, those with 3 hp motors should make 20" diameter cyclones and those with 2 and even 1.5 hp motors should use 22" diameter cyclones. Often these bigger diameters end up requiring mounting the blower to the side as the result would be too tall with a top mounted blower, but regardless they still work very well.

Whoops it looks like I got that the wrong way around. I knew there was size changed required but I was so fixated on the fine dust separation problem that I forgot about the need for the cyclone to be be made bigger for smaller motors/blowers, simply to get the cyclonic action happening.