How to Build an Inexpensive Air Filter for your Bunker

Topics in this category pertain to planning. Discussions include how to prepare yourself, your family and your community for catastrophes and what you plan to do when they hit you.

Moderator: ZS Global Moderators

Post Reply
User avatar
Stercutus
* * * * *
Posts: 13600
Joined: Wed Feb 10, 2010 8:16 pm
Location: Time Out

How to Build an Inexpensive Air Filter for your Bunker

Post by Stercutus » Sat Aug 31, 2019 7:01 am

I have to give him props although I probably wouldn't use tennis balls due to their textured surface maybe not providing a good seal. All things considered for a low cost manual pump it looks to be useful if your preps include preparing for chemical leaks and otherwise contaminated air that you might not be able to escape in time.

He has some interesting vids on his channel.

You go 'round and around it
You go over and under
I go through

User avatar
raptor
ZS Global Moderator
ZS Global Moderator
Posts: 16804
Joined: Sun Mar 04, 2007 10:18 pm
Location: Greater New Orleans Area

Re: How to Build an Inexpensive Air Filter for your Bunker

Post by raptor » Sat Aug 31, 2019 10:06 am

That is intetesting. BTW you can buy activated carbon airfilters at many places. These will also remove to some extent additional harmful gases. I doubt they are NBC approved but like a lot of things it is not an all or nothing proposition and every bit helps.

CrossCut
ZS Member
ZS Member
Posts: 168
Joined: Mon Mar 18, 2013 6:32 am

Re: How to Build an Inexpensive Air Filter for your Bunker

Post by CrossCut » Sun Sep 01, 2019 8:48 am

That is interesting. I've considered getting a reversible bathroom fan, so that outside air could be drawn in and well as exhausted to the outside. A HEPA filter, like some vacuum cleaner bag materials if not a rigid filter of the proper size, over the vent. If the home is reasonably airtight it should create some positive pressure inside. Only stumbling block is finding a reversible bathroom vent, the rest would be fairly easy.

User avatar
raptor
ZS Global Moderator
ZS Global Moderator
Posts: 16804
Joined: Sun Mar 04, 2007 10:18 pm
Location: Greater New Orleans Area

Re: How to Build an Inexpensive Air Filter for your Bunker

Post by raptor » Sun Sep 01, 2019 1:33 pm

Instead of a reversibe fan, just install 2 different fans. Install them in line and use the same zent pipe.

User avatar
JayceSlayn
* * *
Posts: 655
Joined: Wed Mar 05, 2008 3:07 pm
Location: North Carolina

Re: How to Build an Inexpensive Air Filter for your Bunker

Post by JayceSlayn » Mon Sep 02, 2019 10:25 am

I'd say that the build in the video seems pretty janky, although some of which I'd forgive if it was just being in a hurry to demonstrate the concept. The build quality could be a lot better, especially if you're worried about air leaks around components (important for this kind of thing), but somewhere in the distant background the theory of a positive pressure air filter for a bunker is going in the right direction. It is probably better than nothing, but noting the above concerns about tennis balls not being ideal as check valves, and watching the smoke still pouring out the outlet in his test, I wouldn't put too much faith in its demonstrated form.

My notes from the video:
  • If you're already buying pipes from the hardware store, just substitute real check valves for the tennis ball contraptions - it will probably cost 50% more per valve, but save you lots of effort and will undoubtedly be better than most things you could cobble together. If you have to build this thing from scrap (e.g. in an PAW), at least strip the fuzz off the balls first - they are nice and smooth rubber balls underneath - or pick something that is already smooth, like a racquet ball.
  • Barbeque charcoal (and any kind of "regular" firewood charcoal like you'd find in the ashes of a fire) is not a "perfectly adequate substitute" for proper activated charcoal. It will serve OK as a chemical filter, but it has vastly less surface area than proper activated charcoal, and so its absorption rate/efficiency and operational lifespan will be dramatically reduced. As noted in the video: bulk activated charcoal isn't too expensive, just get the real stuff if you can. There are ways to make a more improved (though probably still inferior) substitute for commercial activated charcoal at home, but they are somewhat involved.
  • You are probably going to want a lot of "depth" of activated charcoal to sufficiently filter the air you're pulling in, and this does require a fair amount of pressure to move through that restriction at a reasonable pace. A common household fan is unlikely to be able to develop that kind of ultimate pressure - I'm thinking it is closer to a vacuum cleaner or leaf blower than a bathroom exhaust fan. Actually, the blower in a central HVAC might be a pretty good match for ultimate pressure and displacement requirements. The hand-pump is capable of generating a much higher pressure differential than nearly any of these alternatives, so that is a good idea, but it requires the check values because it is intermittent, and it is also a pro or con that it doesn't use electricity, depending on your standpoint.
  • Ultimately, if you are filtering air for something like a house or bunker, you will probably want to have a slight positive pressure inside anyway, and again it may be hard for a typical fan to maintain that. You need to be able to beat the leak rate, which requires displacement performance (i.e. "CFM") while at the same time being able to develop enough positive pressure to ensure adequate, uniform outflow (a fraction of 1 PSI would be sufficient). Spending more time sealing your enclosure would pay off immensely. Also remember that if you are pumping air into a pressurized environment, that will add to the positive pressure requirement of the blower, above that of just the filter restriction.
  • The way he loaded the carbon in a towel and stuffed it down the pipe isn't ideal, and that is possibly why there was still smoke coming through in the test. The towel is pretty thick, and creates a (somewhat low-resistance) path around the circumference of the pipe which air can bypass the activated charcoal completely. A better option might be to section the pipe off using a fine-mesh barrier (a towel could still work), but so that there are no gaps through which air can pass without coming in contact with the filter media. Rough example configuration: ===|###|=== (Key: '=': pipe, '|': air-permeable media barrier, '#': filter media).
Rahul Telang wrote:If you don’t have a plan in place, you will find different ways to screw it up
Colin Wilson wrote:There’s no point in kicking a dead horse. If the horse is up and ready and you give it a slap on the bum, it will take off. But if it’s dead, even if you slap it, it’s not going anywhere.

Post Reply

Return to “Contingency Planning & Preparation”