Thread: Alternative Dust Extraction Solution

Hi Mick
Are you aware that with any Cyclone the Cone and the Fan DO NOT have to be close coupled.

With the CV the motor housing is designed to be screwed directly to the top of the Cone.
However the two can be separated and connected with suitable sized ducting.

I have read somewhere on the web of someone having similar height restriction to you and he used a 90 degree bend and pipe between the cone & blower to lower the total height. You could even put the cone in the workshop and have the blower outside.
This may be a better solution than tilting the cyclone on a 45 deg angle
Ron

Originally Posted by ronboult

Hi Mick
Are you aware that with any Cyclone the Cone and the Fan DO NOT have to be close coupled.

With the CV the motor housing is designed to be screwed directly to the top of the Cone.
However the two can be separated and connected with suitable sized ducting.

I have read somewhere on the web of someone having similar height restriction to you and he used a 90 degree bend and pipe between the cone & blower to lower the total height. You could even put the cone in the workshop and have the blower outside.
This may be a better solution than tilting the cyclone on a 45 deg angle
Ron

Ron,

thanks - I did not realise this.

I'll admit my ignorance - if I can do that, does that move 90% of the noise outside of the shed if only the cone is in the shed? I don't expect to have a height restriction inside the main shed but wanted to isolate the noise to the woodshed which is a small separate shed sitting right outside the main one. I think I want it all - little noise, cyclone and magic numbers!!! I think I can only get the 'little noise' isolating it outside the main shed and I have a woodshed with height restrictions.

I am still hoping someone will answer whether running a 240volt 3-phase with a VFD (like a CV) can I run below 50hz and reduce the noise? If I had something like the CV Max with a short run to my lathe (the most used and least noisy machine) can I technically run below 50hz with associated noise reduction?

cheers

Mick

Hi Mick
Yes you can run a CV with VFD below 50 Hz. The VFD will run the motor down to at least 10 Hz. I do this all the time with my Bandsaw when I want to cut Steel.

However if you reduce the speed then you also reduce the air capacity which somewhat defeats the purpose of having the cyclone to collect fine dust.

Going from a CV1800 ( 15" fan) to a CVMax ( 16" fan ) will help the airflow but running below 50Hz will still reduce the airflow of both.

The CV max at 50Hz has approximately the same air capacity as a CV1800 at 60Hz. This is why the CVmax was originally designed: to cater for countries with 50Hz power.

When VFD's became common and cheap most Au users now run their CV1800's at 60 hz to increase the capacity back to the American standard, in fact many CVmax users also now use a VFD and run at 60 Hz to increase the capacity even further. Unfortunately increasing the speed to 60Hz also increases the noise level.

That is why I wish I had bought a CVmax to run at 50Hz instead of a CV1800 at 60Hz. Both would have the same air capacity but the CVmax at 50Hz should be quieter. I have three phase power and could have eliminated the VFD which would have made the price much the same.

My CV1800 is getting close to installed, at least to where I can turn it on. I have a Sound level meter and will measure my CV1800 at both 50Hz and 60Hz and will post the results. May take a week or so.
Cheers
Ron

PS In regard to your Q regarding the source of the noise I am not sure whether most of the noise emanates from the Cone, the Fan, or the Exhaust. John sound proofed his fan and russel added a silencer both of which worked so the Q is unanswered. Maybe either may respond with their thoughts

My experience with the CV is that noise from the cone is quite low. If you look back at my CV post (sorry, not sure how to link) you will see how I have surrounded the impeller housing which is full of Sound Batts. This together with the muffler I built was what I found was needed to get the sound down to a level I was comfortable with.

I have since been told that on most electric motors the cooling fan is bi-directional because the manufacturer does not know what the direction will be in the final installation. If the final direction is known a different fan can be installed which will greatly cut the motor noise. If this is true it is too late for me because I would have to pull the thing half apart because the motor is to close to the roof do do anything about it.

If I understand the question, yes, you can run it less than 50 which I have done to clear the air after operations. On my VFD it is just a matter of turning the knob down.

Originally Posted by ronboult

In regard to your Q regarding the source of the noise I am not sure whether most of the noise emanates from the Cone, the Fan, or the Exhaust. John sound proofed his fan and russel added a silencer both of which worked so the Q is unanswered. Maybe either may respond with their thoughts

I can assure you the greatest source of noise is the exhaust ... by a long way. The next biggest is the impeller. Forget the cone altogether.

For reasons that escape me Safari had more trouble than I did suppressing exhaust noise. Two layers of HVAC insulated duct (8 inch and 12 inch, one inside the other) plus a bit of insulation around the impeller dropped the noise for my cyclone from 97 to 65 dB. I stopped there, because most of my machines are noisier than that.

You may be getting needlessly hung up on noise. My CV runs at 65 dB and I can't hear it when running the table saw or drop saw or the thicknesser etc. For my money, once the dusty is quieter than the machines it services, there is little point trying to reduce noise any further.

Before you go any further, measure the noise levels of you vac, and your wife's vac. It may surprise you. Remember, a 10 dB reduction in noise level halves the noise. I dropped my noise from 97 dB (naked) to 65 dB. That's an eight fold reduction.

VFD
Chris told me not to run the VFD below 40 Hz, because we might not get enough cooling air drawn over the motor. At 40 Hz, a lot of airflow is lost. It kind of defeats the purpose of installing something like a CV.

Cheerio!

John

Ron, safari and John,

thanks for the replies and help. I'll do some more investigation in regards to separating the cone (leaving in big shed) and impeller (put in small shed) but the CV is sounding a more likely option for me. It also sounds like the CV max is a better long term option.

BTW, do any of you (or anyone else ) know if by decreasing the Hz, this reduces power consumption? I need to increase my power/electricity knowledge but in my research I could not find anything that answered this question (maybe there was not enough commercial gain).

Also, do people expect (or know) if the CV Max at 50hz is quieter than the CV1800 at 60hz?

I am extremely appreciative at the help I am getting here.

thanks

Mick

Hi Mick
I cannot help you with the noise levels of a CVMax
I will be able to measure a CV1800 at 50 & 60 Hz and would expect any change to be common to both.
Ron

Originally Posted by ronboult

Hi Mick
I cannot help you with the noise levels of a CVMax
I will be able to measure a CV1800 at 50 & 60 Hz and would expect any change to be common to both.
Ron

Ron,

that would be fantastic . If it is 'easy' how about at 45 and even 40? I think it is just academic but I will consider running one lower when on the lathe if the noise drives me nuts or I don't think it is necessary or maybe so I can still hear my music

thanks

Mick

Some thaughts on lowering the speed of motors and blowers.

I regularly lower the speed of common computer style fans by reducing the voltage for use in noise sensitive areas, but with any reduction in speed and noise there comes a matching reduction in air flow.
Coventional fans are fairly linear.....half the voltage, half the air flow and half the noise.

Because a VFD is used to reduce the speed there will be inefficiencies in the motor associated with the magnetic paths being designed arround 50 or 60 Hz...how this plays out.....that is a serious engineering question and will probably vary from motor to motor.

Depending of how specifically optomised the blower is, the air flow behaviour will differ.
crude straight bladed open faced blowers as found in common dust extractors will have a fairly linear speed to air flow response in the middle of their curve....a highly optomised blower may have a fairly peaky speed V flow curve and the air flow may drop off considerably with speedreduction ...then again an efficient blower may not..depending on how it is designed and what compromise has been made.

All centripital blowers will drop of at some point as the speed slows and there is insufficient mass of air being moved..likewise they will all drop of at the top end as they cavitate.

Depending of where on the curve and how that blower is designed, what the effects of varying the speed will be

Of course all this is dependent on back pressure.

Yes it has been mentioned that cooling air over the motor may be an issue.....particularly if the way the blower responds to speed reduction is unfavorable, to the motors now very much reduced efficiency.
This motor designed to run at 60 Hz, now running at 30 hz for example will be dropping in efficiency considerably.....that energy not delivered as power to the blower will be disipated in heat

Remeber all these motors are designed around running at 50 or 60 Hz.....if they where motors specifically designed to be widely variable speed..they would be much more expensive.


Then if we are talking about cyclones.....they all require a certain airspeed and air flow within the cyclone to be efficient......if the airspeed drops, the seperation efficiency plumets.....to the point where the cyclone is worse than a well designed still air box.

When I first built my 2 inch cyclone, I tested it by sucking up the nearly full contents of it predecessor....around 20 litres of crap ranging from shavings and chips to fine dust from the sander.....before doing this I thoroughly cleaned the vac that powers it......after sucking up nearly 20 litres, there was only a very fine film of dust on the inside of the stanless vac barrel and nothing visable on the needelfelt filter.......that would have to be up in the high 99.X% region......but that is with an open hose and full air flow.

Because I quite often use items that reduce the air flow, the seperation efficiency can be very much poorer than that..with my sanding machines, I regularly have to clean caked filters..so the seperation efficiency particulay in the fine dust may be down in the low 90%......and that is not flash at all.

So reducing the air flow in cyclones may actually be defeating the whole point......you may have just as easily built a still air box.......in still air boxes, as the air speed drops the efficiency increases....and there is no loss of suction or airflow if they are designed correctly.

Realy......running AC motors and blowers AND cyclones underspeed is not very clever......you get inefficiency every where you look......you are better running the RIGHT SIZED system at the speed it is designed for.

As far as noise is concerned.....this is an air handling system.....and what we know as noise is air borne......of course most of the noise will come out of one end of the pipe or another.....the noise may be made somewhere else in the system, but the majority will come out the ends of the pipes.

Remember a siren is just a badly designed centripital blower, and turbulance is a major source of noise..so every bend and "T" in ya pipes makes noise.

I am surprised that there has been no discussion about mufflers.....these can be easily made with common plumbing items.
Remember if you have some sort of enclosed output filter on your cyclone, that will work well as a muffer.

As for the matter of the blower being remote from the cyclone.....actually the further from the cyclone the better.
Sucked or blown, blowers create turbulance, maximum efficiency in a cyclone is achieved with smooth flow in and out.
It is generally considered that the input pipe should be straight and clean for at least 3 times the diameter of the cyclone....and the longer and straighter large center riser pipe comming from the cyclone the better.

Most large indistrial cyclones the blower is not mounted on the cyclone.

It is generally considered that there is less suction loss by blowing air into a cyclone, BUT the blower is disadvantaged because it must then be a material handling blower........a sucked cyclone can use a more efficient but more fragile blower.

If ya not buying a complete cyclone with a top mounted blower, then there is a very good case to mount the blower inside the shed and the cyclone outside.....this has been common in industry for decades....or if a sucked cyclone..mounting the cone inside the shed and the blower in a housing on the roof.....externally housed pipe mounted blowers are far from uncommon in fume cupboard instalations

The noise from the actual motor is small.
When I work at the lathe with an open hose next to the tool rest, the air flow into the end of the hose is noisier than the 1.5Hp blower 3 metres away.

Of course that all changes if you are using a 4 or 5 Hp motor to do the same job.

cheers

My CV noise readings, taken 3 M from the impeller at head height, were:

1. 50 Hz: 55-56 dB.
2. 60 Hz: 64-66 dB.

So, dropping from 60 to 50 Hz halves the noise level.

My 2 HP shop vac recorded about 70 dB.

Seeing as we are discussing alternatives.

Has anybody considered, still air boxes, tortuorous path seperators or bag shaker boxes..all are used in industry in one form or another or in combination and some are easy to build.

Of course there are also options other than the conventional conical cyclone.

Yes there are the crude drum seprators...that can be some combination of crude cyclone and or crude still air box, but mostly little real thaught or design goes into them...and mostly they are far from efficient.

But all of them have advantages over a cyclone in one application or another or for one reason or another.

I mentioned the still air box.....while it will never match a good conical cyclone running at optimum air flow......it will handily spank a cyclone in the area of suction loss and will be every but as effective as a cyclone where there is irregular airflow.
Its just a big box of very large crossection in comparison to the ducts, the idea is the air slows considerably and the dust falls out of suspension....simple efficiency can be gained by making the exiting air rise.
The centre cylinder in a cyclone is a still air chamber.

A tortuorous path seperator is taking the still air box and making the slow air negociate a path that promotes the dust dropping out or several stages of still air.

A shaker box or shaker house is a container that has the bags or filters in the top and a container in the bottom, there is an eliment of a still air box, and the filters are constantly or intermittently shaken.....a simple box han be made like this and the bag shaken manually by a stik or lever.
Many of the big dust collection systems being installed these days are shaker houses.

Then there are the non conical cyclones, like the plate cyclone.
where the top half of the drum looks a bit like a conical cyclone but perhpaps a sloped up side down bucket shape and there is a plate between the upper compartment and the waste drum.
This is a considerable improvement over the crude drum seperator.

As I say none of these will match a cyclone running at the correct air flow for seperation efficiency, but all are real and commonly used alternatives and all can be built very cheaply.

cheers

I made my own cyclone as per BP, the cyclone/cone itself doesn't make any real noise, most of the noise is from the exhaust. I made a muffler for the exhaust which did reduce the exhaust noise, don't have any before or after numbers, the fan housing would be the next noiseiest, the amount of noise is a function of fan design, speed of rotation and the interaction the fan has with the housing, e.g. How close is the fan wheel to the fan housing, there are engineering solutions here to reduce this noise. I made up an enclosure around the fan housing and motor using some freezer panel, more for wheather protection than noise but certainly reduces any noise from there.

This chart shows what happens with changing the speed of the fan,...... more reading if you want, just google Fan Laws and fan curves

Note! If the speed of a fan is increased with 10%

• the volume flow increases with 10%
• the head increases with 21%
• the power increases with 33 %

Or another way to put it is flow is proprtional to speed, pressure is squared with speed and power is cubed with speed,
or
if the fan speed is 1 unit we get 1 unit of flow, ......for clarification the actual speed doesn't matter, the point is if we increase speed the result is as per above
if the fan speed is 1 unit we get 1 unit of pressure,
if the fan speed is 1 unit we use 1 unit of power,

But
if we double the fan speed from 1 unit to 2 units we get 2 units of flow,
...............................................................................4 units of pressure,
.........................................................................use 8 units of power

The most efficient solution in terms of power consumed and air moved is to operate the fan at it's designed parameters, that is when all factors are known, e.g. how much flow is needed, the ducting layout including all fittings (bends/blast gates) lengths of pipe, lengths of hose, fan speed, dust hoods etc. however for the average woody DC that is on the shop floor the fan would be something that is designed for an average range and therefore may or may not be operating at it's most efficient in the average woodies dust extraction system. The operating point is movable (to get more flow) if we do things like reducing system pressure (larger pipe/less length of hose) but if pipe size has already been increased the same degree of benefit may not be achived if we further increase pipe size, what is interesting is the values of power, pressure and flow when the fan speed is less than 1 which suggest low pressure, low fan speed gives us max flow for least power, which suggests a fan wheel that is larger in diameter rather than smaller and or a fan that is wider rather than skinny is better than speed increase, but further reading shows us that increasing diameter costs as well in power consumption.




Pete

In $ terms what does that all mean if we go from 50 to 60 hz,
from the fan laws we get P1/P2=(n1/n2)3 p = power and n = rpm 3=cubed
if we have 2850 rpm (n1) at 50 hz then at 60 hz we have 3420 (n2) rpm (assuming linearity)
(2850/3420)3=0.5787
assuming a DC with a 3kw (P1) motor
then P2=P1/0.5787=5.18kw
assuming 30c/kwhr
then if you run your DC for 1 hr at 50hz it will cost 90c
if at 60hz it will cost 155c for an hour
which represents a 57% increase in cost to run the DC at 60hz Ooops just checking this again (155-90)/90*100=72%

I should add that for any given DC your motor may or may not be operating at full capacity, it depends on your system, pipe size, pressures, how clean/dirty your filters are, how closely matched the fan wheel is the the system it is hooked upto,etc,etc.
In the above the thing to be wary of is the increase in current drawn via the wiring. If in doubt check it out with a sparky.


Pete

Originally Posted by John Samuel

My CV noise readings, taken 3 M from the impeller at head height, were:

1. 50 Hz: 55-56 dB.
2. 60 Hz: 64-66 dB.

So, dropping from 60 to 50 Hz halves the noise level.

My 2 HP shop vac recorded about 70 dB.

John,

very much appreciated. It is great to get a feel for what 'will be'. As I have probably already said, I am looking at running the DC as quiet as I can (but still achieving magic numbers) when I am on the lathe but want the 'power' when I need it.

Soundman,

I much appreciate your views and experience. I very much wanted an alternative view (and there always is one) before deciding what I do. Being very much a novice (or an ignorant one as some would say) I wanted a broader understanding before making any decisions. Your write up on motors and making best us of a cyclone was great for me and I will put that in my notes to go back over again. My simplistic view on what you wrote says I should not run a motor much below 50hz for long periods of time until I really know what I am doing (which may be never)

Peter,
yours was what I was after in regards to power and cost relative to to running at specific hz so thank you very much.

So overall if I get something (like a CV Max) that I can run at 50hz as standard and 60hz when I need to then this will cover any expansion or running multiple machines at once.

Cheers and very appreciative once again. There is no way I could have got this far without everyone's help.

My next research is in splitting the cone and impeller and motor for the CV

Mick