Cyclone CFM Rating For Small Shop, and other ?s

[Kent Chasson]

I've read a lot of stuff in the archives but could not find answers to these questions.

I'm in my shop full time and am tired of wearing my respirator several hours a day. I'm willing to put some time and money into a good cyclone system. I have a 600 sq ft, one person shop and mostly use one tool at a time. But I do have a few tools (like a couple of pin routers) that don't direct the dust so greater cfm at greater velocity would probably help. My questions:

Is there any disadvantage, besides cost and noise, of having a system that pulls more air than you need? Does it effect cyclone efficiency? Is it hard on the the filter?

Bill Pentz says it's best to run large lines all the way to each machine. Others say lines should be stepped down to keep velocity up. Who's correct and why?

Any other thoughts about choosing a system? I've been looking at Clearvue and Oneida. Should I look at others?

Thanks.

[Alan Schaffter]

First of all- bigger is ALWAYS better when it comes to a DC- the higher the CFM (at the machine) the more dust you will collect and prevent from wafting into the air where you can breathe it. All components (machine port, ducting, cyclone, and filters) should be sized accordingly. Stepping down has two purposes- one doesn't apply to you- it is to help balance the system when the DC must draw from different machines being used at the same time. (it is also used to balance HVAC systems). The goal should be to maintain as large a duct the DC can handle (for max CFM) from the DC all the way to the woodworking machine. The only reason to ever step down the duct size is to maintain an air velocity adequate to keep the dust in suspension and prevent it from settling out and creating a blockage. The typical velocity required is around 4000 fpm but can be less if duct runs are predominantly horizontal with little vertical rise. That velocity is fairly easy to obtain with a good DC and well designed duct layout that has minimal static pressure resistance. Use a properly sized DC and the most direct runs that minimize bends and turns - this principle most often violated in home shops- you are not looking for neat runs that follow the walls- often a single diagonal run with drops coming off at a 45 (Christmas tree shape layout) is the best. For your shop and a fixed ducted system you probably should look for a minimum 3 hp system with 14" impeller and a cyclone separator and discharge outside if you can or through a dual cartridge filter stack if you can't. You can't go wrong with a ClearVue.

[Chris Strizver]

Is there any disadvantage, besides cost and noise, of having a system that pulls more air than you need? Does it effect cyclone efficiency? Is it hard on the the filter?

You nailed the two disadvantages. Cost and noise...there are no others.

Bill Pentz says it's best to run large lines all the way to each machine. Others say lines should be stepped down to keep velocity up. Who's correct and why?

Neither and both. It depends on what you're doing. Assuming you work alone and have one tool operating at a time, then Mr. Pentz is right. Imagine for a moment that you're a poor woodworker and have only one tool. Would you start with 6" pipe and at some arbitrary point drop down to 4" to keep velocity up? Obviously no as the smaller pipe would do nothing but restrict airflow.

Now you run into some money and get a second tool and add a branch. But that branch has a closed blast gate on it so when you're using your first tool you're still in the exact situation you were before adding the 2nd branch.

In the last 2 weeks I've been hooking up my ClearVue. I can tell you that finding the 6" pipe and attaching a suitable barrel is the hard part -- something you're going to have to do with any unit you purchase. Assembling and mounting the unit was the easy part.

The other hard part which I'll be getting to is building those custom shrouds to capture the dust so it can be collected. You can have 50K CFM and still not suck the dust if you don't capture it first. Quoting Mr. Pentz:

I share a simple game that tries to use air and two straws to move a balloon. One person is only allowed to blow and the other to only suck. The one who blows always wins because they move a directed stream of air that can push that balloon all over. That directed stream of air goes quite a distance before friction will slow down the air. Sucking pulls air from all directions, so airspeed drops off at the same rate as the area of a sphere. That formula is 4 times pi times the radius squared, so it takes moving a huge volume of air make any effect even a tiny distance away. Most of us already know this from using our shop vacuums that will only vacuum up right next to the hose nozzle, but on blow will send dust everywhere. The same thing happens with our fine dust collection. Any fine dust that does not get protected by a well designed tool with a good dust hood and then vacuumed up gets launched by almost any airflow from our blades, bits, belts, cutters, motors, etc. The only way to prevent this is to ensure our tools keep the fine dust controlled then move enough volume of air to capture it before it gets launched

So don't think that getting an over-powered DC will solve your problems. You still need dust shrouds around your tools or you'll be disappointed.

[Kent Chasson]

Thanks for the replies. That's pretty much what I thought on all counts but getting more confirmation helps.

I know my work is cut out for me if I really want to do something worthwhile with my various routers and other tools that spew in multiple directions but I have set aside some time this summer to do that kind of stuff.

Would either of you be inclined to share why you both ended up with the Clearvue over the other options?

[Chris Strizver]

Would either of you be inclined to share why you both ended up with the Clearvue over the other options?

Sure! It boils down to feeling & price for me. I'm sure the Grizzly's and Oneida's perform well. The ClearVue folks just clicked with me. They're a small, responsive business and are guys doing it for the betterment of woodworkers. Even after the business was sold, those values live on. I had the privilege of meeting the new owners at the Portland WW'ing show. I walked off with $50 of tubing with nothing more than a promise to pay via Paypal the next day. I trust my instincts and first impressions and these guys had class act written all over them.

That, in addition to $1,400 got me a system that costs $1,600 on Oneida's site. Maybe the Oneida is worth $200 more, I don't know. YMMV.

[Alan Schaffter]

Would either of you be inclined to share why you both ended up with the Clearvue over the other options?

I don't have a ClearVue, but have a version of the Pentz design, which the ClearVue is based on. It has more of the subtle advanced design features than any other commercial unit.

Someday, someone is going to make these things from injection or vacu-formed plastic (like the Oneida mini) which should bring the price way down. There is no reason it needs to be made from heavy metal or PETG plastic.

[Joe Jensen]

Please do some more research on size. With every system I've researched in the 2-5hp range with cyclone, the design is optimized to maximize CFM. But, you also need suction pressure to move the air. The CFM for most machines is rated with no pipe and a clean new filter (means basically no resistance). Take a brand new 2HP collector from Oneida or any other and put on a 2ft long 4" diameter pipe and measure CFM and you will get between 350 and 400 cfm. Now step up to that bad boy 5HP monster collector from any of the suppliers and do the same thing with the 4" diameter pipe. Guess what you will measure, 350 - 400 CFM. It might be a little higher or a little lower than the 2HP machine depending on the static pressure the designer targeted. Here is where many folks jump to the conclusion that you need to put in bigger pipe. Do another experiemenet. Put on a 6" pipe with a reducer to 4" on the end to simulate a 4" diameter machine port. Do it on the 2HP machine and you will measure 350-400 CFM. Do it on the monster bad boy 5HP and you will get about the same reading. How can this be? It's because the diameter of the smallest passage is the primary determinant of CFM. With the same suction pressure, you will get the same flow.

The CFM ratings are VERY misleading. Doubling the CFM rating with the same suction pressure won't pull ANY more air through a small machine port. Why would a commercial shop with a professionally designed system have a 5HP machine? So they can run more than one machine at a time.

What we really need in small one man shops is a 5HP collector that can pull say 1000-1200 CFM and apply most of the 5 HP to more pressure. My 2HP cyclone generates 11-12 water gauge inches of static pressure and a free CFM of 1200. If I could have that same 1200 CFM and 5 HP my calculations suggest I could have a pressure of 20 water gauge inches of pressure. By the time you factor the losses for the filter and duct, you are lucky to get 2-3 water gauge inches of pressure at the machine port. If you could increase the collector start pressure by 8 inches, you would increase the pressue at the machine port from 2 inches to 10 inches. this would pull like 2X the CFM through the port.

Here are some CFM number for port diameters. Increasing CFM 2X for a given port size requires 4X the pressure.

Here are some numbers from engineering design tables for a well designed system delivering 2-3 inches of pressure at the port.
4" port = 350-400 CFM
5" port = 550-600 CFM
6" port = 750-800 CFM

Remember, a 6" pipe with a 4" port will pull no more than 400 CFM

Moral, with the current collector offerings, getting your machine ports as large as possible is critical. Buying a 5HP collector over a 2 or 3 HP one won't help unless it delivers more suction pressure (static pressure) unless you plan to run 2 or 3 machines at the same time..joe

[Kent Chasson]

Thanks Joe. Everything I've looked at seems to have an increase in static pressure with an increase in HP but it's not easy to compare apples to apples even within one line from one manufacturer, much less between brands. Some post fan curves for one but not all machines. Most just give a single CFM rating at a specific static pressure.

I do plan to increase the port sizes wherever it makes sense.

[glenn bradley]

It is like trying to compare cable TV or cell phone plans isn't it? I have a 2HP cyclone, wish I could've fit a 3HP but just couldn't. I still wear a respirator during the cutting of many materials. As I was foolish enough to operate for a couple of years with only a bag-type DC with the factory bags on it I developed a sensitivity. That is why the mask even though I have the cyclone. Buy the best you can. Once you get to where I am, there's no fixing it; you just try to keep it from getting worse.

[joe aiello]

So how does one go about measuring for CFM?; is there a device that measures for CFM at the port? Anything like an air pressure guage?

[Alan Schaffter]

So how does one go about measuring for CFM?; is there a device that measures for CFM at the port? Anything like an air pressure guage?

It is a calculated value- based on various parameters that can be measured- you need things like a Magnehelic gauge with pressure pickups (pitot tube, etc.) Go to Bill Pentz's site for details.

Also, in addition to what Joe said, probably the biggest factor for CFM is impeller diam. A couple of manufacturers sold DCs with larger motors but didn't change the impeller- guess what- no improvement in CFM. The blower should have as large an impeller as the motor can handle without drawing too much current- one reason why an ammeter is also critical when doing DC testing.

[joe aiello]

Is Clearvue still around? When I enter the Url,I get a DiscoverCard home page?

[Alan Schaffter]

Yup, new owners, 3 brothers, new web site, moved to Seattle.

[Jay Runde]

Yes, check out http://www.clearvuecyclones.com/