Dust Collection system makes a very loud noise

[Geppetto]

Hi All, I hope somebody can help me out in English.
I have made myself a small dust collection system
for a portable Bosch table saw. The vacuum (small 1300W home vacuum) is connected
directly to the collection system and than from there I go to the table saw using a 3 meter
flexible pipe I bought a karwei which looks very similar to a normal vacuum pipe.
It all works great except that this pipe, makes a very loud noise like a wissel, it is so loud that I bearly hear the table saw.

Note: This is a little hobby and I don't need a big container
the pipe in the image was a test, now I have the same material but longer.


Do you think this because of the type of pipe I bought?

 

[houtenklaas]

Is it possible to find out where the whistle sound is coming from? Are you sure all connections are absolutely airtight? If there is a small leak that might cause the sound.

 

[woodworkpro]

Is the hose from the vacuum lower in the cone then where the pipe of the tablesaw goes in.
I can't see it well but is the pipe from the tablesaw in the middle of the cone ? This pipe should be more to the side of the cone, like
the dust deputy cyclon

 

[HoutHans]

Phew, that's a big question. Such noises are - I think - the result of turbulence and that is notoriously difficult to predict and as a result a problem that is very hard to adress. My approach would be to take out or replace components of the system (one hose etc at a time) in order to find out what causes the noise. I agree with woodworkpro that the inlet appears to be insufficiently offset and in line with the perimeter of the cylindrical top of the cone. Bill Pentz has some very useful drawings on his site.

good luck,
hans

 

[Geppetto]

Thanks all for getting back to me and doing it in English.

I will try to address oll the replies, I also have some images to show.
From what I can test the issue is in the hose I bought, if I remove it, like in the first image, there is no strange sound.
As soon as I add the hose back, a short part or a long one, I get the very loud noise again,
I have also sealed the hose to the inlet, with no change at all.

***As for the position of the inlet, it's difficult to make a decent image, however it is positioned on the side of the cone,
in fact it was really difficult to perforate the cone in that area since not being in the center. but once again, it does sound OK withour the extension hose.

Here is just with the vacuum inlet, and works perfect, there is suction and no noise


Here is with a small section of the hose as a test, and the noise started.


Here I have sealed the connection, but the noise did not change at all


and here I replace the short test hose with a much longer one, I still have good suction
but the noise is still there. I also checked the hose for holes, but could not find any

 

[damien]

You could test by connecting the hose directly to the vacuum. It could be the hose, if I see correctly the profile shoulders are square and not rounded, and that could help making noise.

Why does everyone insists on setting the entry at the side of the cone and not using the top?

 

[Geppetto]

You could test by connecting the hose directly to the vacuum. It could be the hose, if I see correctly the profile shoulders are square and not rounded, and that could help making noise.

Why does everyone insists on setting the entry at the side of the cone and not using the top?

Tested and yes the noise is there. I will get a new hose tomorrow.
Question: this hose is 3cm in diameter, if I get something bigger, let's say 10cm
would I lose sucking power?
I found this at praxis :
http://www.praxis.nl/gereedschap-in...xible-luchtafvoerslang/1860915.html#accordion

As per your question, to be honest I am new at woodworking, I do it has an hoppy, and I found
the tutorial of how to make the cyclone with the street cone on Youtube and I thought was cool.
If I knew that I could have connected from the top it would have saved me a lot of swearing

 

[Wim Kluck]

You cannot increase or decrease the size of the hose. This due to different principals. A vaccuumcleaner with a small hose and about 20000 hpa. And the one with the 10 cm hose Works with 1000 m3/h. Sorry but my dutch is a lot better so the story is kept simple.

 

[Marthijn]

Why does everyone insists on setting the entry at the side of the cone and not using the top?

I'm guessing it has something to do with suction. I.e. when you place the hose directly in the middle of the cone you create some sort of a 'cyclone', but when you place the hose off-centre the suction will not create that cyclone.

@Gepetto, could it be that the hose you hose is clogged? I don't know for sure if i'm using the right term here, what i mean is: could it be that there's a piece of paper stucked in the hose?

 

[damien]

Question: this hose is 3cm in diameter, if I get something bigger, let's say 10cm would I lose sucking power?

No, but dust could easily build up in the hose and that can be a fire risk. Maybe it is ok for a straight tube going downhill.
I think going from 3cm to 5cm is a good idea certainly for great lengths of flexible tubes which have large pressure loss.

 

[HoutHans]

Hi Gepetto,

It's good to hear that you have isolated the cause. As to the diameter: there are essentially two different systems: one relies on a large volume and relatively low pressure (HVLP) and that requires large diameters. The diameter of the ducting would be in the order of 10cm for a hobby system. The other relies on high pressure and low volume (HPLV) and that is what you find in most vacuumcleaners. If you increase the diameter too much (like going from 3 cm to 5 cm) you'll still have a large pressure differential between the suction end of your hose and the motor, but a lot of air to move in that wider tube with the result that the air will not be moving fast enough and poor dust collection and - as Damien correctly states - a risk of dust deposition in the hoses just waiting for some static electricity from the combination of moving dust and plastic tubes and causing a dust explosion. You'll want to avoid this.

As to the placement of the inlet in the cone of the cyclone: it needs to be at the outer edge so that the dust comes in at the sides of the cyclindrical top and enjoys the maximum effect from the air that is spinning round on the inside of the cyclone; that will keep the dust on the outside of that spinning air mass so that it won't be sucked up through the centrally placed outlet.

 

[damien]

Respectfully disagreeing with HoutHans.

As a long (4m) 3cm flexible hose can strongly reduce suction, I expect that the practical air speed in the 3cm and 5cm hose to be close. Of course 10 cm is another story. It is not only static electricity, but something like hitting a nail can start a fire and their is plenty of air to push the fire further along. That's why metallic ducting is more interesting.

As for the cone inlet I am pushing my ideas. Bill Pentz uses narrow cones (3 diameters wide), his inlet can be described as a side inlet but just as well as a folded top inlet as he uses an air ramp. In a very wide cone it is even less important what is done, although I expect a side inlet to have a large pressure drop and that can be painfull for a HVLP systems.