Air filters - why not plastic? - Fuel Economy, Hypermiling, EcoModding News and Forum

Peter7307 · 04-09-2008, 10:55 PM

Just bought a new vacuum cleaner for the house.

Unpacking all the bits and fitting them together as per the manual I noticed the filter was made of hard plastic with really small openings.

Having assembled all the pieces and tried the cleaner to make sure it all works I was amazed at the ability of the filter to hold the finest dust.

Now this got me to thinking why can't car filters be made of this material?

At the moment they are pleated paper or some other material which is replaced and the old one ends up in landfill.

Yes I am aware of the K&N brand and a few others which are foam and all need to be re treated usually with oil.

Any thoughts?

Cheers , Pete.

SVOboy · 04-09-2008, 11:25 PM

I wonder if it could be manufactured cheaply enough to make it sensible? What are K&N and the like made out of?

DifferentPointofView · 04-09-2008, 11:30 PM

Layers of cotton gauze, oiled up. Paper filters use 3-4 layers while K&N uses 6 or 7, yet the paper filters better. K&N probably makes a large profit margin. Cotton gauze can't be that much.

Lazarus · 04-10-2008, 12:00 AM

I wonder what size it would filter too. You don't want to let to large a particle in there.

Funny · 04-10-2008, 01:08 AM

As a matter of fact, you guys are on the right track.

I work for a filter media company that supplies most filter companies (Honeywell/Fram, Baldwin, Donaldson, etc.) with the paper they use to make their filters.

Paper (Cellulose, or wood fibers, and glass fibers) is VASTLY more efficient at removing smaller particles.

Oiled cotton gauze (K & N uses 4 layers, I think) lets particle sizes of more than 40-60 microns to pass. That is to say, they can filter smaller particles, just that is the average particle size they capture down to. Heavy duty air filters, like the ones found on semi's and large diesel trucks, filter down as low as 10-15 microns. An average daily driver car, has a filter that filters down to 30 microns or so. The smaller the particle, the less damage it will cause in critical wear areas (bearings, cylinder walls, valve stems, pumps.) This is the reason that diesel trucks run forever. They make sure that there is next to nothing in the oil that can damage the engine. That is also the reason those diesel engine filters are so large. The pores are so small that the flow rate is diminished and you have to increase the surface area of the filter to compensate.

I am a research and development technician that does nothing but test air and lube filters and media for a living. I don't want to sound like a know-it-all, I just want you guys to make an informed decision when choosing something that is going to affect the longevity of your vehicle. I have no brand preference. So I gain no profit from you buying any type of filter. Do your research, look up "beta ratios" and if you search for a particular filters beta ratios, that will tell you what percentage of a specified particle size (5, 7, 10, 15, 20, 30 and 50 are the most common micron sizes used) is being filtered out by that type of media.

I'll be back on at about 6:30am EST. Post any questions here and I'll try to answer them before work. If you couldn't tell already, I don't sleep much

.

Funny · 04-10-2008, 01:12 AM

Quote:

Originally Posted by Lazarus

I wonder what size it would filter too. You don't want to let to large a particle in there.

I'll run this past my boss tomorrow (today

). I know he did a study on the K & N filters and Frams Air Hog series (also uses cotton gauze) a while back and could probably get the data in a jiffy.

Ryland · 04-10-2008, 01:27 AM

Our vacuum uses water as the filter, similar to air filters that use oil, like the old VW's have, they works really well, and can hold alot of crud, and you just dump the water when you are done, if you used oil for your filter you could then have a centrifuge filter at home that spun the dirt out of it, and use it again and again.

Funny · 04-10-2008, 08:05 AM

Another way that is not as common, but is almost as effective, for rating filters and takes 1/20 to 1/100 the time of the beta ratio tests, is the mean flow pore (MFP) rating.
You need a porometer (measures the size of the of the pores in filter media), which aren't that common and pretty expensive

. Barring those restrictions, a porometer is a great way to measure the effectiveness of a filter

.
Here's some of the mathematics behind it. Think of a bell curve. This bell curve represents the different size pores in your filter, and is called a pore distribution curve. The very top of the bell curve is the Mean Flow Pore. This is the average pore size that will be allowed to pass by a filter.
If you were to then take the CFM (cubic feet/minute) flow rate of that filter you were working with, get the square root of the CFM and divide the MFP by the result, you get whats called permeability per pore ratio, perm/pore for short. This is able to be compared to other filters and the higher the perm/pore ratio, the better the filter.
That probably is a lot to absorb, so I'm sorry if I confused you guys, it took me a while to get it too

.
I'll try and get that info for you gents (and gals) about the K&N filters, and if I can get a sheet of the specs/data, I will post them later.