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Outside dust collection

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1K views 17 replies 11 participants last post by  OSU55 
#1 · (Edited by Moderator)
Hello,

I just moved my Powermatic PM2200 dust collection outside of my shop in a covered port. Does anyone know if I need to keep using the bags for the fine dust particles or can I just place a bucket below?

I am wondering if the bag creates suction or anything-your input is appreciated

Cheers

Bob
 
#2 ·
I say try it and see. It is possible that the cyclone action relies on a certain amount of back pressure from the filter and bag to work effectively. On the other hand, if it is outside, you may not care; plus, with less back pressure, it may also give you better suction, which is a bonus.
 
#3 ·
It's on the outlet side of the blower, so you're good to go. The bucket (unless it's connected to the filter) won't do anything, the debris will fly all over the place. Be aware, it will decrease back pressure and could (maybe) allow the motor to draw a few to many amps….so iId check the current draw. If you remove the bag, you may as well remove the filter, nothing will go through it. But to your question: no, the bag doesn't create suction, it might limit it slightly. That said, why do you want to eliminate it? It shouldn't be catching that much dust anyway.
 
#5 · (Edited by Moderator)
I eliminated the useless bags from my HF 2HP DC. Debris went first to a 35 Gal trash can with a plastic vortex lid then, directly outside. The trash can caught the chunks and most of the dust. Minimal dust went outside.
 
#8 ·
I don't see the collection bag as much as an issue. Try it and see.

Before I ever heard about the amp draw thing , I vented my blower outside and have worked in blissful ignorance for 5 years. I've heard people talk about this, but never seen any actual proof. My mind is open.
 
#12 · (Edited by Moderator)
First, I'll warn that the info below needs to be verified (preferably by testing with an amp meter) since I'm going by memory.

I believe that dust collector amp draw increases when there is more air volume around the impeller and decreases as air volume decreases. So removing the filters will reduce amp draw. Running dirty filters will increase amp draw. Closing blast gates will decrease amp draw. Removing all ductwork and leaving the cyclone mouth wide open will increase amp draw and possibly overheat the motor.

The above refers to typical cyclone dust collectors and not shop vacs which rely upon airflow from the hose to cool the motor.
 
#13 ·
So removing the filters will reduce amp draw. Running dirty filters will increase amp draw.
- JAAune
Those 2 points are reversed. Removing the filters will allow the blower to move more air, and increase the load on the motor. Similarly, clogged filters reduce the amount of air the blower can move and decrease the load on the motor.
 
#14 ·
Long as you dont heat or cool your shop it works great. If the breaker does trip due to increased amps you can either address the increased electric load, or add a bit of restriction, like a partially opened blast gate, in the main line to the DC to reduce air volume until the amps drop enough to not trip. Dont put the filter and bag back on, that defeats the purpose (requires maintenance).
 
#15 ·
If you do find need to reduce the amps, I would probably add the restriction on the filter or outbound side so you don't create a bottleneck where the most chips are flowing.
 
#16 · (Edited by Moderator)
I will probably test it later this year since we're planning to exhaust outside after the furnace is replaced (new furnace uses outside air for combustion). The DC is run off a VFD so it's easy to test.

The theory is that dirty filters increase air volume around the impeller (increases resistance) and requires more power to rotate at the same RPM. This is referenced in the linked thread by Will Blick.

https://sawmillcreek.org/archive/index.php/t-61372.html

Since the info I've read is conflicting the only safe approach is to test amp draw and see what really happens.
 
#17 ·
It is a little counterintuitive because when you restrict the air flow on a vac or DC, the pitch increases which sounds like the motor is straining. It is just the opposite. Since the motor is doing less work by moving less air, the motor speeds up while drawing fewer amps. Here is an demonstration.
 
#18 · (Edited by Moderator)
Not sure it matters where the restriction, if needed, goes. Chips have to pass it before or after the blower. If using a separator put it on the discharge since only dust comes through, and since this is for your lathe, only small particles/dust, put it on the discharge.

As far as the difference between a restriction on the inlet vs discharge side of the blower, theoretically there would be some difference in amps, not sure of the magnitude. Assuming the airflow is the same, the restriction on the discharge side would create higher pressure resulting in higher density air which requires more power. It gets a bit tricky though - I said for the same airflow. With higher density air the blower will put more cfm through the system, and draw more amps. Its the change in density or specific volume, not just air volume. The only way to do the comparison is to measure inlet flow ahead of the restriction, and adj the restriction size, inlet or discharge, to achieve the same inlet cfm.

A DC will draw more amps without a filter. this is not the same as described above, because the cfm's are not equal. DC impellers work by imparting momentum to the air. They have a lot of "slip" as restriction builds, unlike a shop vac blower that is designed for higher differential pressure. As a filter clogs, pressure builds and cfm drops, and more air is "slipping" vs being pushed out. and the impeller is actually doing less work. Remove the filter and slip is dramatically reduced, and the impeller does more work pushing the air out.

As a filter clogs less mass is moved, cfm drops. The reduction in cfm
 
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