Suck Vs. Blow: another dust collection question

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Forum topic by AbranV posted 10-30-2013 06:12 PM 1215 views 0 times favorited 8 replies Add to Favorites Watch
View AbranV's profile


30 posts in 2509 days

10-30-2013 06:12 PM

Topic tags/keywords: dust collection delta duct dust collector question

LJ’s. I need to ask for some help here on my DC. I’ve read forums and books, but for some reason the info is not computing. I need some blunt, straight forward info to get it through my thick head.

Here’s my situation I have a 8×14 shop that’s beyond tiny. I have to be very creative with my equipment purchases and floor space. Getting ready to do more work indoors, I’ve taken apart my DC(Delta 50-850)and wall mounted it, motor up, inlet down. I will be building a separator in the next day or two, and I want to vent the exhaust outside.

My questions,

1. Is this a stupid idea?
2. Does the distance from DC outlet to vent kill performance?
3. Going from a six inch outlet to four inch duct kill performance?
4. Can I use flexible dryer duct hose as the outlet run? Or is that not wise?

From my understanding, shorter runs from DC to machine are best. I just want to know if the same is true for the exhaust. Or once your past the impeller and on the way out isn’t as vital.

Your help is greatly appreciated


-- I'd rather be making sawdust.....

8 replies so far

View Fred Hargis's profile

Fred Hargis

4996 posts in 2515 days

#1 posted 10-30-2013 06:51 PM

1: NO,

2: Yes, but it would take quite a bit of length to be a problem.

3: Maybe, a DC that can move lots of air will move a whole lot going from 6” down to 4”. But that loss of air isn’t a problem for a lot folks who are perfectly happy with the performance of 4”. Is this question about the discharge or the runs to the machines?

4: I would not, I would use something smooth like PVC or snaplock HVAC ducting. The above answer to #2 assumes you have smooth wall ductwork for the discharge. Using something that’s not smooth or corrugated will impact the air flow, hence performance.

-- Our village hasn't lost it's idiot, he was elected to congress.

View Don W's profile

Don W

18754 posts in 2589 days

#2 posted 10-30-2013 07:00 PM

I agree with Fred 100%. Will add the following.

You have an 8×14 shop. everything is a short run. (I assume you’re somewhere centered on the 14’)
Stay away from flexible dryer duct hose. Besides what Fred said, it will probably plug.

-- - Collecting is an investment in the past, and the future.

View crank49's profile


4032 posts in 2992 days

#3 posted 10-30-2013 07:06 PM

Resisting Resistance is not futile.
Makes no difference whether the resistance is before the fan, or after the fan.
The restriction of air flow will reduce performance of the collector.
Dryer hose is very poor for air flow. Too wavy inside, creates turbulence and reduces flow.
A 4” pipe will only carry about 44% of the flow of a 6” pipe.
A double 4” pipe will still leave you about 12% shy of equilibrium.

You said you mounted the motor up and the inlet down; does that not leave the outlet running horizontal?
Can’t you rotate the outlet toward the wall and have a very short piece of 6” pipe to get it outside.
OR, is the fan not mounted on the outside wall?

View RobynHoodridge's profile


127 posts in 2351 days

#4 posted 10-30-2013 07:07 PM

What Fred sed.

Think of it like the turbine creating a difference in pressure at it’s position, rather than separate ‘blow’ and ‘suck’. Then you see that restricting either the in or out messes with it’s capacity to create the pressure difference. The suck only as good as is permitted by the capacity to exhaust. So i really LIKE the idea of venting to the outdoors (no restrictive filter on the out end).
I’ve even been thinking of fitting a leaf blower / sucker on the wall outside, with a long hose through the wall and to the dust. Which would vacuum up my messes (through a separator) and then have near zero ducting on the output side.

-- Never is longer than forever.

View kaerlighedsbamsen's profile


1248 posts in 1735 days

#5 posted 10-30-2013 07:15 PM

Regarding point 3:
From 6 inches (18,8 area) to 4 inches (12,56 area) is a near 33% or 1/3 reduction in performance

-- "Do or Do not. There is no try." - Yoda

View crank49's profile


4032 posts in 2992 days

#6 posted 10-30-2013 07:40 PM

6” = (3×3) x pi = 28.27

4” = (2×2) x pi = 12.56

12.56 / 28.27 = 44.4%

We were both using the same 4” pipe, but I don’t know what happened to the 6”.

View UncannyValleyWoods's profile


542 posts in 1885 days

#7 posted 10-30-2013 07:41 PM

I’m married, so I no longer have an opinion on the matter.

-- “If Jesus had been killed twenty years ago, Catholic school children would be wearing little electric chairs around their necks instead of crosses.” ― Lenny Bruce

View TeamTurpin's profile


85 posts in 2083 days

#8 posted 10-30-2013 08:07 PM

The part that concerns me here is the noise level. Any DC in that tight of a space would be deafening. I have a 12 X 16 shop and my HF unit’s noise seemed to fight its way into my hearing protectors. I’m not sure how you’re configured there, but if you have an option to get your DC unit on the other side of the wall, you may be much happier. I was able to build a small vacuum closet onto the back of my workshop and my DC and air compressor now live out there. Life is much better now.

This link shows you how I rigged my DC: Presto!


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