Thread: Moving the DC outside

Ian - I finally got to watch the vid - the noise made by your impeller does not sound right to me and the start up noise it makes is I think a hint as to what might be going on.
It could be that one of the impellers is bent, or a tad longer than the others and this was corrected for by balancing but that means it will produce a different noise than an impeller that has all even length blades. Unless it is something that is clearly visible then fixing this is not easy and it is often just easier to replace the impeller.

You will need much more force than hand force to make a difference.
Try carefully clamping bricks either side of the impeller exit.

It could be the orientation of the impeller/motor.
Try removing the exit ducting and standing the impeller back up on its base and compare that to the SPL with it hanging from the side.

A bracket between the impeller exit and the base of the stand might help.
inside.jpg

Originally Posted by MandJ

what I'm saying is that you can't measure the effectiveness of the DC housing with the complete DE "inside the housing" and measuring DB with the impeller intake port open (inside the cabinet).

Ok. Another set of test. This time I rebuilt the whole DC in the shed, and ducted the input back through into the workshop. As I currently have 6" ducting between the shed and workshop, and a 4" intake to the DC, I did this by running my 3 metres of 4" flexi internally up the 6" ducting. So airflow is definitely restricted but the intake noise is moved out of the DC shed.

73db with the DC on and the door closed
75db with the door open a couple of inches to allow exhaust
81db with the door open fully

Also I measured the intake noise in the workshop at 75db, I imagine its going to be significantly higher with a full 6" duct and unrestricted air flow.

So with the door fully closed, 73db vs my original 77db with the naked input. But with the door open a crack, 75db vs the original 85db measurement, a significant reduction.

After all that, with the door closed and the full DC in the shed (73db) vs only the filter/bag in the shed (68db) is still a significant difference (I am presuming with a proper baffle the end result will be much closer to these figures than with having the door open a crack.

I am going to pick up some freebie carpet offcuts and line the walls, then measure again. If I can get down to 70db at 1m from the shed, then I'll put the whole DC into the shed which will keep the garage quieter!

Also regarding motor noise, I turned it back upright and it doesn't change the vibration significantly. As Bob points out, I may well have a slightly unbalanced impeller or a noisy motor bearing. I don't know how to fix those short of replacing them, and I don't really want to buy another 2hp DC knowing how poor they are at actually collecting all the fine dust. Unfortunately a 3hp unit won't fit in my shed space so I will make the best with what I currently have.

IMHO a 6" pipe with a bell mouth intake will likely be quieter than a 4" intake, usually the smaller the intake for a "given flow rate from a DE" the louder the intake air noise - forcing XX flow rate through smaller and smaller intakes creates higher intake air speed and noise- up to the point - then it drops off as flow rate chokes down.

I got some old rubber-backed carpet tiles and lined the shed with it, including the roof. (Note double stick carpet tape doesn't hold on roof and walls, I will have to get myself a tube of construction adhesive and try again.)

That brought the noise level outside the closed shed down to 70db.

Then I realised that my free download sound meter app has been measuring unweighted decibels and most of the noise is low frequency rumble. So I upgraded it to measure weighted dbA (weighted for human hearing perception), and measured the noise level as 62dbA outside the closed shed. That seems intuitively correct, I don't perceive the noise as overly loud myself.

Ok, I'm now comfortable with finishing the full DC 6" mod and keeping the motor/impeller in the shed too.

Next step is to make a MDF exhaust baffle and a frame to mount the motor/impeller unit.

That's better, I just assumed that the app would be dbA. Thanks for the update.

I've revised my plan with the DC configuration. Rather than building a frame to lift the motor up to the same height as the bag unit input, I'm now going to keep the motor section lower down and connect the two pieces together with 6" ducting.

This works better with my shed configuration as it was going to be a very tight squeeze with the way I've mounted the baffle box internally

I have turned the motor 90 degrees so that the input can come in directly from the side wall of the shed, this saves a 90 degree elbow.

Also I turned the bag mounts 90 degrees so the section facing the shed door doesn't have a mounting pole on it, that will make bag changes much easier. By doing this, I am also cutting out and enlarging the original bag inlet area.

Originally Posted by Ian Dobson

I've revised my plan with the DC configuration. Rather than building a frame to lift the motor up to the same height as the bag unit input, I'm now going to keep the motor section lower down and connect the two pieces together with 6" ducting.

This works better with my shed configuration as it was going to be a very tight squeeze with the way I've mounted the baffle box internally

I have turned the motor 90 degrees so that the input can come in directly from the side wall of the shed, this saves a 90 degree elbow.

Also I turned the bag mounts 90 degrees so the section facing the shed door doesn't have a mounting pole on it, that will make bag changes much easier. By doing this, I am also cutting out and enlarging the original bag inlet area.

Looks very tidy.

Not a biggie because you save a 90º elbow which probably cancels out the following. Usually this arrangement will have some small flow losses because the rotational flow of the air in the impeller is not in the same plane as the bag housing.

It will be interesting to see what SPL you get with this setup.

Originally Posted by BobL

It will be interesting to see what SPL you get with this setup.

Silly question, but how do you measure SPL?

I can make up a u-tube manometer easily enough, but not sure how to hook it into the duct work, or whether the inlet duct needs to be blocked off when taking the measurement.

Originally Posted by Ian Dobson

Silly question, but how do you measure SPL?
I can make up a u-tube manometer easily enough, but not sure how to hook it into the duct work, or whether the inlet duct needs to be blocked off when taking the measurement.

SPL = Sound pressure level - its the "quantity" for which dB is one of the "units".

Manometers measure regular "pressure" , units are things like Pa, psi, bar, etc

Originally Posted by BobL

SPL = Sound pressure level - its the "quantity" for which dB is one of the "units".

Manometers measure regular "pressure" , units are things like Pa, psi, bar, etc

Thanks Bob, silly me, you were talking about flow loss in the previous paragraph then mentioned SPL and I misinterpreted that as referring to static pressure level, i.e. WC"

I will need to get new 6" shed inlet ducting in place before I can measure the noise level again. The new entry point needs to be much lower down so I enlarged the old inlet cutout into a long rectangle and made that the output vent from the baffle box.

Also I need to convert the impeller input over to 6". Not sure how to do the reverse BMH at present ... my largest roundover bit is 1/2" and I haven't turned anything on a lathe in 30 years. I am thinking of a long session with rasps or a sanding drum, but hard to get a consistent profile all around.

Originally Posted by Ian Dobson

Also I need to convert the impeller input over to 6". Not sure how to do the reverse BMH at present ... my largest roundover bit is 1/2" and I haven't turned anything on a lathe in 30 years. I am thinking of a long session with rasps or a sanding drum, but hard to get a consistent profile all around.

1/2" is better than nothing.

The 6" input to the impeller is now installed. I'll fabricate a manometer and take some hard measurements plus redo the noise level check after I get it back into the shed. It certainly seems to be moving a lot more air now.

The next problem maybe that is in fact moving too much air for a single filter to cope with. I’ve added another filter to my modified 2hp and my flow has increased somewhat over the single filter.

No room for a second bag in my shed, but I could swap the bag for a PF if that decreases the back pressure?