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[Equipment] Resmed S9 Filters: Standard versus Hypo-allergenic
Oh yes, they are!
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wow...lets get real for a second.
Go get a brand new filter out of the package.
Now hold it up to a bright light.

See all those pinpoints of light shining through?
Those holes that are 100-150 microns in size. (or larger)

Yup. All the stuff pollen/dust mites/tiny-teeny allergy things you thought the filter is stopping are sailing right through those huge
channels in your filter.
Why is this?
Because the filter isn't for you at all.
It's there to keep major sized dirt particles out of your expensive machine.
That's it.
So clean / replace every few weeks to keep the air flowing nicely so your machine stays happy.

Putting a more effective filter on would only stall out your CPAP blower (stops delivering pressure)
The blower lacks the power to draw air though a very fine filter media.
(see Honeywell HEPA filter / air cleaner)
That Honeywell model #50250 thing actually works but it has a huge motor and blower to do the job AND it makes a fair amount of noise too.

So do not expect a whole lot from your silky quiet CPAP machine because it is doing all it can to
keep you inflated properly.

Peace, love and carrots.
"With ordinary talent and extraordinary perseverance, all things are attainable." - Thomas Foxwell Buxton

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Hi, Shastzi.

You are describing the filter as if it was a sieve. I'm just quoting Wikipedia below:

HEPA filters are composed of a mat of randomly arranged fibres. The fibres are typically composed of fiberglass and possess diameters between 0.5 and 2.0 micrometers. Key factors affecting function are fibre diameter, filter thickness, and face velocity. The air space between HEPA filter fibres is much greater than 0.3 μm. The common assumption that a HEPA filter acts like a sieve where particles smaller than the largest opening can pass through is incorrect. Unlike membrane filters at this pore size, where particles as wide as the largest opening or distance between fibres cannot pass in between them at all, HEPA filters are designed to target much smaller pollutants and particles. These particles are trapped (they stick to a fibre) through a combination of the following three mechanisms:

1. Interception, where particles following a line of flow in the air stream come within one radius of a fibre and adhere to it.

2. Impaction, where larger particles are unable to avoid fibres by following the curving contours of the air stream and are forced to embed in one of them directly; this effect increases with diminishing fibre separation and higher air flow velocity.

3. Diffusion, an enhancing mechanism that is a result of the collision with gas molecules by the smallest particles, especially those below 0.1 µm in diameter, which are thereby impeded and delayed in their path through the filter; this behaviour is similar to Brownian motion and raises the probability that a particle will be stopped by either of the two mechanisms above; it becomes dominant at lower air flow velocities.

Diffusion predominates below the 0.1 μm diameter particle size. Impaction and interception predominate above 0.4 μm. In between, near the most penetrating particle size (MPPS) 0.3 μm, both diffusion and interception are comparatively inefficient. Because this is the weakest point in the filter's performance, the HEPA specifications use the retention of these particles to classify the filter.

Weinmann actually uses a HEPA filter in their machines. It filters 99.5% of particles at 1 μm and 85% of particles at 0.3 μm. It falls in the E10 class (formerly H10) of EN 1822:2009 standards.
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I'm allergic to sarcasm, and mean words - but I still get more of each than I prefer, no matter what type of filter I use Sad
*I* am not a DOCTOR or any type of Health Care Professional.  My thoughts/suggestions/ideas are strictly only my opinions.

"Only two defining forces have ever offered to die for you. Jesus Christ and the American Soldier. One died for your Soul, the other for your Freedom."
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(10-23-2013, 08:03 PM)Peter_C Wrote: I'm allergic to sarcasm, and mean words - but I still get more of each than I prefer, no matter what type of filter I use Sad
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