Thread: Best cyclone dimensions for modified DC-3

I would build a full size BP.

Cheers Barry

Originally Posted by Robbie123

Im about to build a cyclone from sheet metal for a modified DC-3 blower , wondering what people consider the ideal cyclone size would be if running 6 inch pipe, like the barrel diameter and height ? also the length of the cone .

It has been years since I worked all this out for my system, but if the old brain is recalling correctly, for a 2 hp blower he (Pentz) recommends a cyclone diameter which was almost exactly the same as a a 44 gallon drum.

As such, my cyclone is 2 x 44 gallon drums in a timber frame, the top drum has a sheet metal cone in it and the bottom drum is a collector bin.

BP's first design was based on a 14" impeller @ 60hz. If you can find a 3 phase motor and use a VFD you can do the same. He mentions the 14" impeller somewhere on his website but it gives me a headache whenever I go near it so I will leave you to find it. Using the VFD takes away the fixed motor speed restriction, I run mine at 65hz as an example of that and at night reduce the speed to 45hz to prevent annoying the neighbours.

Barry i would like to build a full size but have not got the height , was looking at dust deputy and replicating the size but building more of a barrel on the top.

Bill said that using his design a 2hp should be about 22" in diameter so the cone will be about 36" long. The 3hp is 20" in diameter and a 5hp is 18". The more powerful the blower the smaller the cyclone. His spreadsheet does the design and layout if you fill in the blue boxes, then you need to mark up your sheetmetal and get to cutting. It will be bigger than a Dust Deputy or any of the others little cyclones marketed but it is going to be the most efficient.

Dust Collection Research - Cyclone Plans

Pete

So realistically the dust deputy people buy dont work properly on small systems but the sellers so they do

If building a cyclone I would always use a 3 phase motor because of the extra control it gives and the reduced current demands on start up. The CV requires under 20 amps mmentarily using a 3 phase motor but nearly (I believe) over 50 amps momentarily for a single phase motor. I don't know that I have ever seen power draw numbers on a generic two stage system.

Originally Posted by Robbie123

So realistically the dust deputy people buy dont work properly on small systems but the sellers so they do

I've written the following on numerous occasions but seeing as you are relatively new I will repeat it again.

Small 3rd party cyclones on small DCs have two significant problems in regards fine dust, which is why I would not use one in my shed

1) They rob a significant amount of air flow. It is simply is not possible to determine the flow loss just by putting a hand in front of a open duct connected to the DC. The net result is they don't grab as much air and fine dust at source which leaves it behind in the shed

2) They don't separate out as many of the fine dust particles from the sawdust stream. It is not possible to determine this by looking at the dust that comes out of the cyclone as most of the finest dust is invisible. This is not a problem if the Cyclone/DC is vented outside but this then means longer ducting which further reduces the flow.

The amount of sawdust in the soft drink bottle top shown in the photo below is more than enough to contaminate the air in 4 , 6 x 4 x 2.7m sheds to above the recommended OHS levels for wood dust. These standards are ~ 50 years old and make no allowance for greater Aussie wood toxicity, age or other health conditions. If basic healthy air quality standards are used that amount of dust would be enough to contaminate 40 such sheds.

Softdrinkdust.jpg

There is one benefit of using a small cyclone and that is to keep the DC filter bags from clogging up for very long periods so cleaning the filters is one less chore to attend to, but this is a false benefit if much of the very fine dust never gets collected in the first place. One thing that small cyclone owner don't realise is that to maximise air flow the filters should be shaken out after every few cyclone bin empties anyway.

Most non-cyclone DC owners with filters do let their collection bags fill up too much before emptying them and by then the filters can be quite clogged. The collection bags should be emptied when they are no more than 1/2 - 2/3rds full - if they fill up too quickly a bigger DC is needed.

A smaller DC/cyclone MAY produce enough flow to be suitable for small machine like a small belt sander or power tools, or machinery like DPs that don't produce much fine dust.

I would of thought one would need a smaller cyclone less hp but obviously works the other way round. So if i did make the cone and body shorter would it not be so efficient at separating fine dust which then would still get to filter and block up is this correct?

I will putting it in an enclosure outside so no problem with the fine dust getting through the filter and me breathing it in, But would it still clear the dust from the machinery being a smaller cyclone?

So really I'm better off buying a 3hp and that will eliminate all the dangerous dust. And I could also make a smaller cyclone?

Some people have mounted cyclones on an angle to reduce the height at the sacrifice of wall space, although there is nothing stopping you from placing filters or other tools in those spots.

There are also horizontal cyclones but none of them are marketed to home shops. Ground Plate (GPC) Cyclone Dust Collector | Aerodyne Environmental. I contacted them and they did send me the dimensions because I think they thought I was going to buy but I never kept it. They don't have it published on their website. There was enough information to make a homemade version and as I recall the diameter for a 5hp one was very close to a 45 gal/200L drum. They do have youtube animations of how they work so you could experiment and make one for yourself. I don't know how efficient they are compared to the ones Bill Pentz designed. The certainly couldn't be any worse than the stubby ones on the market now.

Here are a couple other links to horizontal cyclones of different designs that do give a few dimensions but not any internal bits, although one shows a cone inside that hints that there is more.

Cyclones – KICE, Industries If you clock on Horizontal Separators it takes you to this one with some dimensions. https://www.kice.com/wp-content/uplo...Separators.pdf

Horizontal Cyclone | American International Manufacturing Co. - Woodland, CA and their dimensions. http://www.aimfab.com/wp-content/upl...yclone_dim.pdf

You can search for more if you want to be a pioneer. If an efficient horizontal could be made it would be a home run for shops with height restrictions.

Pete

Originally Posted by Robbie123

I would of thought one would need a smaller cyclone less hp but obviously works the other way round. So if i did make the cone and body shorter would it not be so efficient at separating fine dust which then would still get to filter and block up is this correct?

I will putting it in an enclosure outside so no problem with the fine dust getting through the filter and me breathing it in, But would it still clear the dust from the machinery being a smaller cyclone?

BillP's recommendation to scale the cyclone with the inverse of fan power is about keeping the airflow high, it's not about separation efficiency.

The pressure drop across the cyclone decreases with the fourth power of the scale factor. For example, scaling all dimensions by a factor of 1.1 (10% increase) causes the pressure drop to decrease by a factor of 1.1^4 = 1.46 (a 32% reduction). A smaller fan has less pressure so decreasing the pressure drop oc the cyclone helps to compensate for that.

Collection efficiency is another thing. Collection efficiency is highly dependent on particle size distribution and so is not really an appropriate parameter for characterizing a cyclone. What is used is a parameter called the cut size. That's the particle size that has a 50% chance of passing through either outlet. Bigger particles tend to be collected in the bin while smaller ones go to the filter (or wherever you're sending the fan exhaust). Cut size varies with the square root of scale factor cubed, so that 10% increase in dimensions would cause a 15% increase in cut size and thus a decrease in collection efficiency.

Sorry about all of the details, but I wanted to demonstrate one of the fundamental tradeoffs in cyclone design, that is, pressure drop versus cut size.

There are plenty of other designs that offer low pressure drop with much less height but the separation suffers. So your tradeoff is really filter cleaning interval versus air flow rate given a fixed height requirement and fixed fan power.

The problem with many (all?) of the statements comparing the Clearvue/BP cyclone with the other smaller commercially available cyclones is there is little to no hard data to compare. I have the 5" Super Dust Deputy. Oneida do not produce a pressure curve for this unit. As far as I'm aware neither does Clearvue. So how do you compare them without pressure loss curves?

It's worth pointing out that the Dust Deputy is a much more recent design than the Pentz design, which is now many years old. It's likely the DD designers were able to take advantage of more sophisticated computer modelling than what BP had at his disposal when he designed his cyclone. They may be MORE efficient than the BP design. We just don't know. They are certainly very good for their relatively small size.

There's no doubt the cyclone is the biggest loss in my system as measured with the power meter. But it was more than offset by replacing the needle felt bag with two pleated filters. And I CAN tell that by placing my hand at the inlet! There's substantially more airflow.

Any system is a compromise. If you have the funds for a 4HP+ blower and a Clearvue cyclone, plus the room to mount it, I would definitely go for it. If you're looking for a good (not perfect) system a 3HP blower, 6" Super Dust Deputy and pleated filters will be excellent.

Originally Posted by Chris Parks

He mentions the 14" impeller somewhere on his website but it gives me a headache whenever I go near it so I will leave you to find it.

Yes, BP's website does that to me too. It's a mess.