Thread: The Generic 2HP DC

Regarding large radius bends - what would be the suggested radius ? Is 640mm too tight?

Cheers

Originally Posted by Lappa

Regarding large radius bends - what would be the suggested radius ? Is 640mm too tight?

Cheers

To tight for what?

Maybe have a read of this.
DRAFT: FAQ - Dust Extraction (Practical Aspects)

For 6" ducting at nominal air flows rates a 1.5R 90º bend has an length equivalence of about 12ft of straight duct.
A 2R bend has an equivalence of ~7ft of duct and 2.5R has an equivalence of about 6ft.
A 640 mm radius of curvature for 6" duct is equal to 4.2R - hard to say how much more of an improvement you would get.

Length equivalence values for large values of R are complicated from the fact that frictional losses for larger radii of curvature bends are eventually overtaken by the reduced duct length of a long curve versus the extra pipe needed to make sharper right angle bends.

Of course the path length of a curve could be shortened considerably by using a couple of 45º bends and a diagonal (shorter length) of duct, and the argument can start all over again.

A major problem for using large values of R in a small workshop is that they take up large sweeping areas of space.

If you get one I would be interested to know the improvement in flow.

"Too tight for what?"

There have been a number of posts suggesting the use of large radius bends rather than the normal 90 degree bends to reduce loss in the ducting. BP even gives rates for corner R as you have indicated. I'm just trying to optimise my system.
I can buy 150mm pipe in long radii ranging from 635mm R to 12 metres R so basically I was asking whether the 640mm R was worth purchasing in place of the existing corners ie. was it too tight a radius and make no difference, should I go larger. I do have the room to replace two DWV 90o corners with two 640mm R corners

The rest of your reply seems to indicate that large radius corners aren't going to make much difference to what I already have so maybe I should save my money even though they are 2/3 the price of the ones you showed.

Originally Posted by Lappa

"Too tight for what?"

There have been a number of posts suggesting the use of large radius bends rather than the normal 90 degree bends to reduce loss in the ducting. BP even gives rates for corner R as you have indicated. I'm just trying to optimise my system.

It depends what you mean by "normal".

These ones are about 1R - these will slow down the flow.
90degreesharp.jpg

These are better ~2R
90degreeround.jpg

You can also make your own very large radius of curvature bends for very little cost
Heres one that is ~2.5R
Mens Shed Dust Collection

I can buy 150mm pipe in long radii ranging from 635mm R to 12 metres R so basically I was asking whether the 640mm R was worth purchasing in place of the existing corners ie. was it too tight a radius and make no difference, should I go larger. I do have the room to replace two DWV 90o corners with two 640mm R corners

The rest of your reply seems to indicate that large radius corners aren't going to make much difference to what I already have so maybe I should save my money even though they are 2/3 the price of the ones you showed.

If I could get them cheap, and you have the space in the shed I would use them.

Back in 2011 I got some cheap 150 mm 15º bends and used 3 of these plus a 45º to make the 90º angle entry from outside to the inside of my shed.
I simply could not use 6 of them to make the full 90º bend because the radius of curvature would have been be too large and I would not be able to come in under the roof truss.
That was when I found out how awkward they could be in a small shed and that's why I haven't been able to use any more of these in my shed.
Now I see they cost $18 ea! so it would be cheaper to make the entire bend.

Mine are the DWV units - similar to your pic of the ~2 R.

BobL, Im using one of your 6" BMH's on the inlet to the DC. It will get a new MDF cover on the impeller. Question is, is there enough lip on the lathe-moulded BMH's to secure its face-to-face with the MDF? ... a few small screws/bolts perhaps?

Also, I did read once that you had a preference for the distance of the inside of the impeller cover to the impeller itself for noise/power... it certainly wasnt "right on it" but more like a gap of 15mm or so... I cannot find that post. Can you recall the number?

Originally Posted by Lappa

Mine are the DWV units - similar to your pic of the ~2 R.

In that case it's marginal that a much larger radius would help.

Originally Posted by woodPixel

BobL, Im using one of your 6" BMH's on the inlet to the DC. It will get a new MDF cover on the impeller. Question is, is there enough lip on the lathe-moulded BMH's to secure its face-to-face with the MDF? ... a few small screws/bolts perhaps?

Yes there is enough lip to do this with small screws. It would also be possible to stretch the PVC by another 5mm all the way around to provide a truly flat section to connect into into.

Also, I did read once that you had a preference for the distance of the inside of the impeller cover to the impeller itself for noise/power... it certainly wasnt "right on it" but more like a gap of 15mm or so... I cannot find that post. Can you recall the number?

Is this the thread you are talking about
New Blower for gas powered forge

Bear in minds that impeller setup is different to those in DCs.

In this case there is no inlet ducting and the BMH is on the outside to ease the pathway of air from all around the outside of the impeller housing into the inlet.
On a DC impeller inlet there is a duct and the BMH is on the inside to ease the flow of air from the duct onto the impeller blades.

I just started with a 16 mm gap and was going to reduce it to see what happened but ended up with way more flow than i needed so I never took it any further.
I ended up lending that impeller to my Nephew for his charcoal forge and this reminds me to get it back before it gets lost.

Is there any advantage/disadvantage at running a generic 2hp dusty at 60 HZ?

Yes provided the pipe is capable of carrying the air you should get ~20% more flow across the board but it won't change the fan curve shape - in other words, a 20% increase of "very little" is still "very little".

How do you proposed to run it at 60Hz?

It was just a question that came up in a discussion re generic 2hp in OZ and the USA. If it doesnt have a centrifugal start switch then there are cheap off the shelf controllers that should do the job.

Originally Posted by Lappa

It was just a question that came up in a discussion re generic 2hp in OZ and the USA. If it doesnt have a centrifugal start switch then there are cheap off the shelf controllers that should do the job.

The 2HP DC motors I've looked at have all had centrifugal switches,
I'd be a bit wary of cheap off the shelf controllers as they usually drive the motor at low efficiency which could end up damaging the motor.
The way to do it would be to swap the SP motor for a used 3P motor and drive it with a VFD.
I though of doing that for a couple of seconds on my 3HP setup but I didn't think it would be worth the investment.

I decided to upgrade the outlet to 150mm all the way to the separator but not open it up to 150mm yet. This brings the restriction down to just 200mm in length rather than the whole plastic outlet, hose etc.

IMG_0588.jpg

The needlefelt filter has been well and truely conditioned since I last posted so the overall flow, with the line to the table saw disconnected so I have my straight line duct to minimise turbulence, has dropped approx. 31 CFM before the mod.

Surprisingly I achieved a increase of 18 CFM with the new outlet arrangement.

Next step was to open the rectangular air inlet to the saw table and that gave me an increase again of 21 CFM.

My main concern with opening the separator to 150mm is whether the filter and bag can handle the higher airflow. Most larger systems with 150mm pipes as standard, have two filters and two bags.

Guess I can do it then block it off if it doesn't work.

I'm going to try a mod I have seen on the new Jet extractor - a deflection plate in the separator. A number of people have done it and claim better separation but they haven't been measuring air flow which I will do before and after the mod.

Probably still flogging a dead horse, but it's interesting to see the results of each different mod.

Cheers

That deflection plate thing would be interesting. You see a few comments on other American forums talking about them, but none I've seen offer any definitive proof.

It will be interesting to see if they do in fact deflect more fine dust into the bottom bag, rather than to the top filter. My filter seems to fill fast and requires the 10-spins every hour.... Bit of a PITA!