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Old 01-07-11, 05:11 PM   #1
phantomcow2
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Is a fan more efficient "pulling" or "pulling"?

The question is in the title: is it more efficient to mount an air filter "ahead of" or "behind of" the fan? Obviously the latter configuration makes for a pulling setup. Is it more efficient than pushing, or is it the same?
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Old 01-07-11, 05:15 PM   #2
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pull is better, especially if you use a shroud to elongate the distance from the filter intake to the fan blades.

1: the air has more room to get pulled evenly through the filter, which results in more surface area being used and that results in less power loss from the filter impeding air flow.

2: moot point and negligible, but the fan will be cleaner, giving better fan blade aerodynamics.
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Old 01-07-11, 05:27 PM   #3
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Awesome post, thanks! I live in a house with four other college students, and people like to smoke hookahs in our basement during parties. THe smoke gets drawn up and a few people complain, so I'd like to build an air purifier via activated carbon to remove that smoke so everybody is happy.
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Old 01-07-11, 05:33 PM   #4
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especially if you use a shroud to elongate the distance from the filter intake to the fan blades.
Pardon my ignorance, but could you please explain or link me to literature explaining this?
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Old 01-07-11, 05:38 PM   #5
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Awesome post, thanks! I live in a house with four other college students, and people like to smoke hookahs in our basement during parties. THe smoke gets drawn up and a few people complain, so I'd like to build an air purifier via activated carbon to remove that smoke so everybody is happy.
Probably much easier to exhaust the air rather than purify it. Got any windows in the basement? Open one and set up a fan exhausting air near the hookah session area.
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Old 01-07-11, 05:44 PM   #6
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Probably much easier to exhaust the air rather than purify it. Got any windows in the basement? Open one and set up a fan exhausting air near the hookah session area.
Agreed.
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Old 01-07-11, 05:48 PM   #7
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Probably much easier to exhaust the air rather than purify it. Got any windows in the basement? Open one and set up a fan exhausting air near the hookah session area.
No,he needs the windows to grow the bong-fodder.
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Old 01-07-11, 05:50 PM   #8
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No,he needs the windows to grow the bong-fodder.
hahaha nice. There's only one window, and we don't want to open it because it's cold outside (I'm in Northwestern PA). Also I really enjoy having a project.
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Old 01-07-11, 05:55 PM   #9
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Pardon my ignorance, but could you please explain or link me to literature explaining this?


do you notice how immediately in the front or behind the hub of the fan, there is little to no air flow?
a long shroud alleviates the dead spot.

assuming it's a regular axial fan and not a centrifugal or cross flow type.
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Old 01-07-11, 06:05 PM   #10
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That makes sense. I'd like to build a wooden enclosure to house a prefilter, hepa filter, and 10lb reservoir of carbon, the air passing through in that order.
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Old 01-07-11, 06:36 PM   #11
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if you're going to do that much filtering, you might want to look into the cross flow fan.
it's a lot better than axial and centrifugal styles for suction.

centrifugal is better in push mode.
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Old 01-07-11, 06:44 PM   #12
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Seems a lot less complicated for you and friends to "hooka"your hash outside during parties.


"8 years of college down the drain"
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Old 01-07-11, 06:51 PM   #13
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if you're going to do that much filtering, you might want to look into the cross flow fan.
it's a lot better than axial and centrifugal styles for suction.

centrifugal is better in push mode.
My feeling is that this much filtering is needed to remove smoke -- the filters for the particles, the carbon for the gas.
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Old 01-07-11, 06:56 PM   #14
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Old 01-07-11, 07:21 PM   #15
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lol nobody here does opium. I suppose the level of filtration I seek would be suitable for such a place, though.
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Old 01-07-11, 08:11 PM   #16
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My feeling is that this much filtering is needed to remove smoke -- the filters for the particles, the carbon for the gas.
yeah, I'm just commenting on the amount of pressure required to pull air through all those filters.

see, there is total flow, and then there is pressure. Very similar to how watts, amps and voltage works.

Axial fans are good for high volume, but as soon as you start impeding it with filters, its performance drops significantly.
Centrifugal fans are really good at pushing air, but require a lot of material to match the total volume of axial fans.
cross flow fans are what you'll normally find in air filters and they're not good for total volume, but have a lot of pressure.
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Old 01-07-11, 08:58 PM   #17
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lol nobody here does opium. I suppose the level of filtration I seek would be suitable for such a place, though.
"Sure kid,next its only Maryjane,then Smack,or a little Angel Dust just to keep up with the crowd.You hit bottom finally waking up out of a narcodic induced stuper at a frat party with your drawers at half mast and a raging pain in your bung hole........................................"

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Old 01-07-11, 09:22 PM   #18
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burn the couch in the living room and the basement smoke odor will be undetectable at best, or negligible at worst.
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Old 01-08-11, 07:29 AM   #19
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The question is in the title: is it more efficient to mount an air filter "ahead of" or "behind of" the fan? Obviously the latter configuration makes for a pulling setup. Is it more efficient than pushing, or is it the same?
First thing is this: You can't "push" the unfiltered air into the filter. You can physically, but the components of the fan, motor, shroud, etc get all gummy and crappy with the unfiltered air. This is common sense.

Look at your forced air furnace set-up. The air filter is the FIRST barrier to keeping the mechanical workings free of dust and crap. Ideally, the filter will be ahead of all duct-work as well. This way the ducts stay clean thereby keeping the system clean. With a shrouded system like a poster described earlier, any opening in this system will be the easiest place for contaminants to be introduced into the system by the physics of its opening being an unfiltered intake.

I don't answer many questions in the BF's but when the question becomes related to my like of work, I will answer them.
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Old 01-08-11, 08:12 PM   #20
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I know the title to this thread was "Pulling or pushing". What happened to it to become "pulling and pulling"?
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Old 01-09-11, 03:48 PM   #21
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That makes sense. I'd like to build a wooden enclosure to house a prefilter, hepa filter, and 10lb reservoir of carbon, the air passing through in that order.
Why the carbon filter. Smoke and charcoal filters = heat and can be to the point of fire. I would leave out the carbon filter.
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Old 01-09-11, 04:41 PM   #22
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I know the title to this thread was "Pulling or pushing". What happened to it to become "pulling and pulling"?
Some helpful mod.
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Old 01-10-11, 02:33 PM   #23
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+1 on having a filter before the fan mechanics. If one looks at ceiling fans and fans in a computer, the blades attract dust very quickly except on surfaces that are actually hitting the air (the leading edge).

Like what was previously posted, I'd consider putting the filters in front of the fan mechanism and have it suck from your bong-shelter that way. The ideal thing is to just vent it out and consider spending some cash to heat the incoming air.
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Old 01-10-11, 03:27 PM   #24
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Yea I'm definitely convinced -- the entire filter mechanism will go before the fan. As discussed, it's more effective for the fan, and of course it'll save the fan from getting contaminated with crap or whatever else.
Thanks again for the helpful replies; I would have been using an axial inline duct fan if not for this. I'm going to hunt for a ~750CFM centrifugal fan to pull it all through.
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Old 01-10-11, 03:55 PM   #25
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