Thread: External DC - finding best of bad options

Originally Posted by pjt

The take home here is that even two 100mm hoses doesn't cut the mustard, . . .

Good work Peter. Given that most systems around only use one 100 mm hose I think that is a bit of a worry.

Your results also highlight the fact that as soon as a 100 mm hose/duct is installed anywhere in a system with larger ducting it becomes the rate limiting step.

The machinery manufacturers are also limiting our attempts at better DC. All WW Machines should come standard with at least one 6" ports (and reducers) and be redesigned to breath so the 6" ports are affective.

Originally Posted by BobL

Good work Peter. Given that most systems around only use one 100 mm hose I think that is a bit of a worry. Yes, definately. Once again from the chart to make a 4" hose/pipe work you have to have probably 20+" and a velocity of 8000fpm (off the chart so guessing a bit) a humungas screaming vacuum style of thing

Your results also highlight the fact that as soon as a 100 mm hose/duct is installed anywhere in a system with larger ducting it becomes the rate limiting step. Yep, this principle is exploited in many areas of fluid dynamics, anyone who has done race engine mods will know that to change the air/fuel mix you change the jet (restriction) as this will only allow a certain amount of fuel thru even tho it is screwed into a large main line.

The machinery manufacturers are also limiting our attempts at better DC. All WW Machines should come standard with at least one 6" ports (and reducers) and be redesigned to breath so the 6" ports are affective. Yes again, and DC's that are able to achieve ~ 6" of pressure and flow of ~1200 to 1500cfm at the machine so that when we put our piping systems together we then get the 1000cfm at the machine, this definately points to these 1 and 2 hp DC definately aren't upto it and it also confirms what BP promotes.

Just as a point on the difference on the hood mod, when I used the same thicky with the 100mm hood it certainly did collect chips/dust? When I remade the hood with two hoses there was a definate difference in the flow and how much better the collection was, in operation I see now that any chips that are thrown out onto the infeed table (within ~3" of the hood) are now sucked back into the hood and I should also see another improvment if I changed the two hoses to 125mm.


Pete

Originally Posted by BobL

All WW Machines should come standard with at least one 6" ports (and reducers) and be redesigned to breath so the 6" ports are affective.

Dream on Bob but hope is forever eternal I guess and we all have that. I spoke to several manufacturers representatives in the last twelve months and they are of the opinion that what they produce works. When confronted with a different view they shrug their shoulders and close their ears. The topic as far as they are concerned is redundant as the ports provided are adequate.

BTW can any tell me how the 5" port on some DE's was actually arrived at. Even in the US 5" is an oddball size.

Oh, that is such nice stuff Pete, especially after the interaction/commentary with Bob. This is the kind of empirical data stuff that could get written up nicely somewhere - even on the WWF Wiki, if it was functioning - and be used as reference material for when the 4" vs 6" discussion comes up.

Mini, my Felder has 120mm ports - maybe it's a European thing?

Originally Posted by Mini

Dream on Bob but hope is forever eternal I guess and we all have that. I spoke to several manufacturers representatives in the last twelve months and they are of the opinion that what they produce works. When confronted with a different view they shrug their shoulders and close their ears. The topic as far as they are concerned is redundant as the ports provided are adequate.

I don't even dream about it because can fully understand their position. Nowhere in any standard does it say that any woodworking machine or DC have to meet the very basic 5 and 1 mg/kg dust spec. It is left up to the workplace to meet this spec so it's the workplace that has to provide the necessary DCs and Hoods etc that provide this. Until this changes I expect that nothing will happen.

The 5/1 mg/kg spec is basically a crock anyway since it does not consider particle sizes. Given the very expensive cost of air particle testing this is in the "way too hard/expensive basket" for most business. I expect woodworking dust related health issues to be highly masked by other environment factors such as motor vehicle emissions (Did you know that Diesel exhaust has now been official classed at carcinogenic, before now it was "probably carcinogenic") so I'm not holding my breath over this one.

Heres a pic of the bend that collects the larger bits
big bits in elbow.JPG
This tells me that there is enough velocity to carry these sized bits up ~2m of vertical 100mm pipe (DWV sewer pipe) and along another few metres of horizontal100 and 200mm pipe and then there's not quite enough velocity to carry on up the last little bit before the DC, if I had 6" main I might get away with it but I don't so the solution is more airflow which I need anyway
I am not having any success with the utube thing, I opened an account and loaded the vid but it just was in processing mode for a couple of hours, looked like it was doing somethig but I don't know
Mini, my felder stuff has 120mm ports also.


Pete

Must be a European thing I guess.

Originally Posted by Gunnaduit

Oh, that is such nice stuff Pete, especially after the interaction/commentary with Bob. This is the kind of empirical data stuff that could get written up nicely somewhere - even on the WWF Wiki, if it was functioning - and be used as reference material for when the 4" vs 6" discussion comes up.

I made an attempt at testing my system a while back, I was directly trying to measure flow but came up against a few hurdles, but with this current discussion I just did the static pressures and then using Bob's chart got some fair results, was quite easy to do, just stick a tube into the duct then the other end onto one utube leg and measure off a scale.


Pete