# Question: In the plant based air purifier, could airflow go the other way, using an unmodified pump?

warren asked on October 08, 2016 19:25
116 | 3 answers | #13538

### What I want to do or know

I'd like to try to build the plant based air purifier and I have a pump, but I'm wondering if we could push air through instead of pulling, so a pump could just be used as-is?

Hi! Nice to digitally meet you.

I asked Nick about that when I did my build because I had the same thought. The only downside he mentioned was that there could potentially be activated carbon blowing out if the pump is not reversed. Presumably if pulling air through the diffuser, then hose and through the now-outlet of the pump w/ a tiny fibrous filter the potential for carbon spewing may be reduced. I don't know if that is true, but reversing the pump was easy so I went with it.

I'm not really sure what size particle would be of concern or whether the fiber filter has any effect on it? What kind of microdust does activated carbon give off & how much of a concern is it? That might be worth its own question.

The other thing I saw in one of the papers was that the vacuum pulled (drawing air down through the plant) may have been leftover from another design where the air was then pushed up an exit column and subjected to a UV light in an attempt to kill any mold spores present. With positive pressure inside that would be impossible because the air just would go everywhere.

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Yes, i also don't know much about this, and if the airflow from the pump is enough to make it a concern... i guess any negative pressure is better than any positive pressure, though! I think it could be especially bad if the plant dries out.

What about putting the growth medium and/or carbon in some kind of cloth bag? Just wondering about exploratory, outside the box (pot?) possibilities. Thanks for thinking through this with me, and great to digitally meet you too!

Yes, please do post a question about active carbon, if you could -- i'm interested as well.

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Re: water level, The commercial version has a low water sensor that shuts the fan off to let it try to survive. It won't resume air circulation until the water level comes back up.

I too wonder about carbon containment (at the bottom of my post I have a couple questions about that), mostly for efficacy. Maybe I'll try a food based glue on the growth medium to stick the carbon in the layer I want (but still give roots access).

Oh, i had another idea -- what about a water-permeable fabric drawstring bag? That'd be pretty easy to put on, but would it impede airflow? Anyhow, i guess it bears some testing.

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I did see one on Amazon the other day and it was more like a mesh bag so it might even let roots go through it. I'm not sure it would do anything specific for particles though.

@nshapiro also pointed out that it would be easier to break your pump by flooding it if you used it in the usual "push" mode. Just so I understand, is that a consideration /against/ modifying the pump?

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Just linking in @nshapiro's comment here:

@Odie91that's a great question and one that many people ask. I'm concerned that if we don't reverse the diaphragm we might risk suspending dust from the growth medium in the air (the pump has a small filter in it so sucked air would reduce that risk). But there are many reasons why you might want to let it stay as a pump: 1) it is safer to water (no risk of sucking water into the pump and ruining it if its pumping air out) and 2) you can pull more HCHO into the system if you have a pump on the ground while the plant is in the window as HCHO is heavier than air.

In this build, we didn't see an instruction to reverse the pump, so we worried about the hose going underwater and making bubbles. Is that a big problem? Like, is it a problem if it bubbles through the water before entering the root area? Someone said it could create carbonic acid, but doing this is pretty normal in a fishtank with plants, so... we weren't sure.

Of course this would make a difference if the pump were sucking from the hose:

This was a lot of fun to build.

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Actually i wondered re: @nshapiro's note on might risk suspending dust from the growth medium in the air if, and this is weird, but putting a filter over the plant container top could help at all? Like, some plants grow through an X cut in a fabric sheet. I just wondered about if putting such a cover would reduce the risk of growth medium dust getting blown around.

In general, I'd think the dust might get tamped down by the water, thinking of how construction sites sometimes spray water to tamp down the dust. But not sure - maybe that's pretty cursory and doesn't even work well.

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Although honestly probably just the whole thing tied up in a cloth bag as I suggested above might be easier to do than rubber banding a filter over just the opening... bears experimentation!