BeFree filter – weird results of the filter integrity test

[Jan Rezac]

I just bought a BeFree filter (replacing an older one), and I encountered the following issue when I tested it. I’d be interested in your experience with the test.

I wanted to check it thoroughly before I take it outdoors, and I also tried the filter integrity test described in the manual. One should not be able to blow air through the filter back into the bottle when the filter is wet (with a full bottle upside down, so that the filter is submerged).

I found I can blow some air in (some pea-sized bubbles) when I blow hard. I repeated it even after filtering several liters of water and letting the filter in the water overnight, so the filter definitely was not dry. I had thought I got a bad piece, so I returned it to the shop and got a replacement.

What’s weird that the new filter behaves the same, I can blow about the same amount of the air through. Moreover, I was replacing a two year old filter just because it did not pass this test – I thought it was damaged. Unfortunately, I discarded it before I bought the new one.

Overall, it seems unlikely that I had three filters, two of them brand new, fail the same way. I’m sure there must be a pressure limit at which the air breaks the surface tension and gets through the pores, so maybe I’m blowing too hard?

I’m going to contact the manufacturer, but in the meantime, I’d be interested in your experience with this test. Is there anybody else that can reproduce this problem with a filter that should be in a good condition?

 

[Ryan Jordan]

Jan – your filter is probably fine. I froze my filter to failure and then repeated the test and in the case of a filter that has big cracks in the membrane, it’s really easy to blow bubbles in it. If I blow hard enough, I can get little bubbles on new and undamaged filters as well.

[Jerry Adams]

did you intentionally freeze the filter?

did you first shake all the water out?  I think the hollow tubes should survive freezing, because they expand anyway when you backflush.  The problem is when there’s water in the other volume outside the hollow tubes, then there’s no place to expand and the case is not flexible

at least that’s my theory

I’m thinking Squeeze here, but I assume Be Free is the same

[Jan Rezac]

Jerry,
these were brand new filters as I brought them from a shop and tested at home, wetting the filter thoroughly.

Ryan,
thanks for your confirmation that it is possible to blow through a new filter.

It would be great if we can collect such observation from more BeFree users. If the test works as Ryan described, it is a valuable information that can save others from throwing away a perfectly good filter.

[John Vance]

Jan, I experienced the same thing as you have with the new filter. I did not discard my old filter and have continued to use it without any problems in terms of illness – about the only “test” I have available to me beyond the blow test.

[Ken Larson]

Jan to provide you some confidence using the filter contact Katadyn:

[Ryan Jordan]

Jerry – I intentionally froze the filter, full of water (to test to failure).

[Jan Rezac]

Ad others witnessed the same thing, I now assume the filter is ok. It will be very unlikely that multiple brand new filters were bad. I just wonder how katadyn answers my questions.

In the meantime, a bit of scientific research… Bubbling through a filter is a commonly used method for determining the pore size – it’s easy to find a simple formula relating the pore size, pressure and surface tension of the liquid. When I calculated the pressure needed to blow through a 0.1 micron filter in water, it is way, way above the pressure a human can achieve. There must be some other mechanism how the air gets through.

A possible hypothesis is that some part of the filter is, despite all my efforts, still not wet. It could happen where the tubes of the filter touch the plastic case – the surface energy would prevent water from filling the gap, leaving a “dry” patch larger than the individual pores, where the air could pass more easily.

That’s where I’m now – still, it would be great if more people confirmed that the filter behaves like that.

[Jerry Adams]

thanks, good experiment Ryan

I’d like to try freezing a filter when all the water is shaken out of it.  There would still be water in the hollow tubes

I suspect this would not damage the filter

If so, that would be really useful information, make the filter a lot more useful

I can see why the filter manufacturer would not like this.  If someone didn’t properly shake the water out and the filter was damaged, that person would complain to the manufacturer

easier to just say not to freeze filter

[Jan Rezac]

I now have a final proof that the filter is OK. I took it on a trip, used it to filter some very suspicious water and survived in a good health. Among others, I took the water from three sources that were obviously problematic. It was not intentional test of the filter, but there simply was nothing better because of a combination of a lower elevation and drought.

I wouldn’t have done it if I didn’t know that my previous filter behaved the same and I had no problem, and if others didn’t confirmed that it is no exception.

I contacted Katadyn three weeks ago, describing the issue and asking for advice, and I got no answer. I’d expect a better support, especially for a product one’s health depends on.

I also wonder how many returns they get from users who, like me, read the manual and perform the test described there before they start using the filter. The instructions are clear – if you can blow through, the filter is bad.

This lesson cost me one filter and some time spent getting the newly bought one replaced. It could all be prevented if the manual was real.

[Jerry Adams]

” I took it on a trip, used it to filter some very suspicious water and survived in a good health”

That is not a good conclusion

Often times you can drink bad water and not get sick.  Some people have better immune systems.  Some people have better immune systems at different times.

What looks like bad water may not have enough microorganisms to be dangerous.

If a bunch of people drink untreated suspicious water, some of them will get sick after drinking enough.

You could take a sample of the untreated and treated water and count the number of microorganisms with a microscope.  Obviously most people wouldn’t want to do that.  Labs do that.  You really have to rely on lab tests of a particular product.

Too bad there isn’t a solution with dyed particles of a particular size.  If the treated water is colored, then the filter isn’t working.

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