DEC RK05 HEPA Filters

[Sean Caron]

On Wed, 13 Apr 2016, Rick Bensene wrote:

> Bill Degnan wrote:
>>
>> I replaced my filters a little while ago, I was concerned about original filters'
>> deterioration, perhaps these will have decomposed over time even if not in
>> use. So I found a newly-produced filter, documented here:
>> http://vintagecomputer.net/browse_thread_record.cfm?id=588&tid=1
>>
>> But basically 3M Filtrete #0412560 carbon pre-filter cut to match the original,
>> from a tracing.
>>
> The filter Bill replaced is the external dust filter.  While good to replace, this isn't the internal HEPA filter that Michael wrote about replacing on his RK05 drives, and that he found available on eBay.
>
> The HEPA filter is inside the drive.  It is a filter designed to capture very tiny particles yet still be a minimal restriction to airflow.  To get to the HEPA filter, you have to take the bottom cover off of the drive.     The filter is quite large, and as mentioned, there are two different types depending on the age of the drive.   If they haven't been replaced in a long time, they should be replaced, as they eventually do clog up with particulates.  When this happens, it can restrict the airflow to the disk platter area, which can lead to dust particles ending up on the platter, and that can result in head crashes, which are most unpleasant.   Sadly, the manufacturer of the HEPA filter stopped making them a long time ago, and they can be hard to find.  I do believe some manufacturer was making reproductions of them for a time, but I believe that they are no longer doing so.  So, finding the filters today can be tricky.
>
> -Rick
>

I haven't worked on such myself, but please be careful and wear a pair of 
heavy gloves when servicing the HEPA filters in these old pack drives. I'm 
reminded of a quote from Ralph Klimek's Burroughs page at Monash:

"They used HEPA absolute filters were a biohazard because they could trap 
bacteria and fungal spores. The manuals warned about avoiding injury, with 
good reason. Once a used filter I was removing slipped and I grabbed it. I 
cut my hand on the dirty side of the filter element. The cut became 
infected and did not heal for nearly half a year! A filter that sat idle 
for a a couple of weeks would smell like a mushroom farm as the trapped 
fungal spores would spawn and begin eating the trapped dust."

http://vm-118-138-243-85.erc.monash.edu.au/fixing-the-burroughs.html

Best,

Sean