Now that we know how to clean the internal lenses, we should be done, right? Our particle counts are up, there's nothing else to worry about except lasers and circuit boards failing? Not so fast.

You know how vacuum cleaners have two filters, a pre-motor filter (or bag) and a HEPA filter? The reason the pre-motor filter exists is because the motor draws dirt into itself as it moves dirt from the floor to your bag or dust cup. And since motors get hot, maybe some of that dirty air is used to cool the motor itself? Wouldn't that destroy the motor? Surely we wouldn't be that wasteful, right? Well surprise: we are.

(If you've ever forgotten to put back the pre-motor filter or bag in a vacuum cleaner and it sounded funny, that's the sound of a vacuum cleaner's motor being destroyed.)

There are bypass motors, but that requires a separate air stream, making it impractical but for central vacs or other heavy duty equipment.

Now have a look at the PortaCount pump schematic, as described in the manual. Do you see a separate air stream for the pump?

So it's a standard pump that only takes in dirty air for everything. Great. And if you follow the tubing inside the PortaCount, you are lead to the internal inline filter (sometimes called the internal zero check filter) before it leaves the PortaCount to the left of the two ports you plug your tubing into:

And here are the two bottom pre-pump filters:

Of course, TSI says you can ignore these filters, but that's inadvisable, because, for one, TSI doesn't service 8020s anymore, and for another, based on what we know about vacuums now, it would probably be a bad idea. We want to extend the lives of the PortaCounts we have access to now, since new CPCs are shockingly expensive. And even if we could find replacement pumps, getting to it would entail disassembling the PortaCount. Not exactly fun, while also knowing how rare these things are...

So, now that we've established these filters may be important, how do we know when to change them?

Signs you may need to change the three PortaCount filters...

("May" because this is anecdotal as opposed to empirical. While I can't prove you need to change your filters, you wouldn't want to damage your PortaCount now, right?)

The easiest way to know when to change the filters (and probably what TSI does, I guess) is to disconnect the inline filter at the back and do a fit test with another PortaCount to verify a fit factor above 50,000. However, that's a bit of a hassle, you need another PortaCount, and there's always the chance that somebody swapped the low-hanging filters making the PortaCount appear less used than it actually is. (Yikes. We'll get back to that later.)

So instead, here's a checklist you can follow to take a guess as to whether you may need to change your three filters (bottom two and back inline), mostly involving excess age, some obvious, some unexpected:

• First: Check the printed dates! Try finding the calibration date, or, if it's not visible, the manufacturing date. An older date ≈ more usage ≈ change the filters.
• Another sign you may need to change your filters is it takes over 15 minutes to get to 1000 particles/cc. It's a sign your 'internal lenses' are dirty, == excess age.
• If you've cleaned the sampling cone and got higher particle counts, you should probably change the filters ASAP.
• If you got a bunch of dead zero-check filters with your PortaCount. It's either a sign of excessive fit testing, since isopropanol is not friendly to these types, or someone swapped your internal inline filter and didn't tell you. (Yikes, again.)
• You've never been able to reach over 500,000 FF with a candle. It should be relatively easy to reach this number with a candle, due to the amount of particles put out by it. And if the PortaCount has had few hours put since its last calibration date, you should be able to reach 999,000 FF too. Not reaching at least 500,000 could be a sign of heavy use.
• The "Service" message pops up on a non-humid day. Could be a sign of anything really (probably excess age with dirty filters, so avoid treating it like a check engine light).
• Look at the screws of the bottom two filters. In the last few years 8020s were serviced, TSI swapped from 3/32 hex bits to flat head screws for securing the filter covers. If you see hex bits, well, you know what that may mean.
• PortaCounts with dirty pumps are annoyingly loud. If your PortaCount sounds like an air purifier at medium-high power, that's probably bad news for your PortaCount pump, but at least you can start minimizing the damage.

Open the bottom two filters. Again, 3/32" hex or flat head. The filters should not crumble in your hand and you should not see any debris in the filter cup. If you do, well, at least you know you may need to change the filters.

(Please don't leave debris in the PortaCount.)

Obtaining and Checking Filters.

Here's the good news: You can use basically any moderately effective 1/8" tube filter for the back inline filter. Most zero check filters designed for CPCs or zero checking come with an adapter for 1/8" to 1/4" OD barb tubing, allowing you to hook up any inline filter the PortaCount uses, be it for zero-checking or for post-pump filtering.

Of course it's not the most critical filter since it comes after the pump, but I prefer changing it anyway simply because it prevents dust near the exhaust port flowing back to the pump when the PortaCount is off.

• You can get a second zero check filter from ETA Filters, which include the 1/8" to 1/4" OD adapter, and can be used for daily check zero counting, maxing out the PortaCount and giving a perfect fit of 999,000.
• Or, if you've already got a zero-check filter, and its adapter, you can get decently adequate 02FA06A filters from Grainger, or aftermarket ones from vendors like Fluitek, for $10-15 cheaper. These filters will only reach into the 50,000-150,000 range for fit factors maximum, but that should be more than adequate for keeping dust from flowing back into the pump.

If you're going to take out the 1/8"-1/4" OD adapter to check the internal inline filter, you do so at your own risk. Make sure you don't get any dust in the adapter; any significant air bubbles could impact your zero filter's ability to act as a zero check. And no, duct tape is not an adequate alternative.

As you can see, these filters are pretty accessible, which is why they might have been changed on your PortaCount, screwing with your ability to properly rate the age of your filters, especially the bottom two filters, because yikes:

The bad news: The bottom two filters are waaay more obscure. The dimensions are quite odd: 1/2" inner diameter, 7/8" outer diameter, and 1" height.

Personally, I only managed to find a filter with a 1/2" inner diameter, 13/16" outer diameter, and 1 1/8" height. Although this filter was slightly off dimensions wise, it still managed to work in my PortaCount. Unfortunately, there are only a handful of these filters available on the new old stock market, which is why I won't be telling you what these filters are. If you need any, you can either DM me (@fediversefittester@fedia.social). You likely won't be able find them on Grainger, or even the aftermarket manufacturers like Fluitek, not unless there's a massive demand of filters for rare, PortaCount 8020s. Lucky you if you manage to find a new filter that's exactly 7/8" wide and 1" tall. I only stumbled across some slightly imperfect filters by sheer luck.

(And good luck having a filter supply when public health officials ignore the fact there's still a pandemic going on...)

So check your filters everyone. Don't turn your PortaCount (or vacuum cleaner, lol) into e-waste prematurely by neglecting your filters.