# What could be causing this difference in suction....



## Marv (Nov 30, 2008)

I have a Delta 1 1/2 hp 50-760 with an Oneida Super Dust Deputy Cyclone and 5" metal pipe. There is a 5" Y fitting on the cyclone with one line going directly to my table saw about 3 feet away with a 5" T that splits to a 4" line for the saw port and a 2 1/2" line to my overarm blade guard (each with it's own blast gate). Today I switched from using the table saw to using the router table (about 12 feet from the dust collector on the other side of the Y) and realized I forgot to close the blast gate for the overarm blade guard. When I went back to close it I noticed the suction sounded louder than it normally did so I figured I hadn't opened the router table blast gate yet however when I went back to the router table the gate was in fact open already. After a little experimenting I found something interesting...there is more suction at the 2 1/2" line on the blade guard when I open it along with any other 4" blast gate down the line than there is when I open it along with the saw cabinet 4" blast gate that is fed off of the same 5" branch. :confused1: Any ideas as to what may be going on here?


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## 44260 (Aug 29, 2013)

I am no where near an expert on dust collection systems but my guess would be that you were "starving" the dust collector for air flow. The 5" Y on the dust collector is probably 8" or 10" at the collector itself, by only using 1 of the 5" lines you are restricting the air flow by half. Remember a dust collector works on air flow.
Thanks for posting this problem though, you may have just helped me resolve a problem that I am having with my dust collector.


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## Marv (Nov 30, 2008)

Thanks for the reply and I'll see if I can explain better! The cyclone inlet is 5" and there is a 5x5x5 "Y" attached to that. One 5" hose goes directly to the table saw where it is split to a 4" and 2 1/2" while the other 5" line goes to the machines on the other side (all are reduced to 4"). When using the table saw I open the 4" gate to the saw cabinet _*and*_ the 2 1/2" gate at the blade guard with all others being closed. What I found is that when I open one of the 4" gates off of the second line and the 2 1/2" gate on the blade guard there is more suction at the blade guard than when I open the saw cabinet gate and the blade guard gate which ore on the same line. Not sure what the reason is and just curious if anyone has any ideas!


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## Toller (Dec 30, 2007)

FWIW cs at grizzly told me to open a blast gate on a different branch than the one I was using. The increased air flow lets the impeller spin faster and will put better air flow on the one I am using.
Probably thesame idea.

Ive never done it on purpose, but I don't fret about leaving a blastgate open accidentally.


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## Marv (Nov 30, 2008)

Thanks Toller and I tried that however suction gets even weaker at the blade guard. Still hoping one of you physics gurus has an idea why this happens!


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## ryan50hrl (Jun 30, 2012)

With an additional gate open your allowing faster airflow in the main line. I'm going to venture a guess if you measured it, your static pressure at the blade guard decreased, but your air speed sped up as the volume traveling through the impeller increased.


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## woodnthings (Jan 24, 2009)

*over blade dust collector*



Marv said:


> Thanks Toller and I tried that however suction gets even weaker at the blade guard. Still hoping one of you physics gurus has an idea why this happens!


You may have noticed that I use a separate shop vac for my overarm dust collector. That's because a shop vac has a higher velocity.... "more suction" than a "Y" off the dust collector. By restricting the pipe size you loose your airflow over the blade, regardless there won't be that powerful type of suction on the DC line anyway. Just use a shop vac one time and you'll see what I mean. Mine are on outdoor remotes, so I don't have to go over and turn them on manually and the Jet 1100 DC has a remote also. 
http://www.woodworkingtalk.com/f7/dust-collection-woodnthings-shop-part-1-a-20273/


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## Marv (Nov 30, 2008)

Thanks guys! I have plenty of suction at the blade guard Bill however I was just curious as to why it increased when I opened a gate on a different line (I'm going to borrow some test gear just to see how much difference there actually is). 
BTW Ryan, I saw your post about stabilizing your router table on the uneven floor without having to shim which is what I now do as well. I'm getting tired of bending over every time I move it so I designed a simple "4 wheel self leveling" mobile base that I'll post as soon as I get it done.


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