Request for help - Covid related

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28 Dec 2011
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Apologies if this is in the wrong forum.

I am a police Sergeant on a specialist team, dealing with CV-19 deaths and disorder, so obviously fairly high-risk at the moment. We have got hold of a load of Sundstrom respirators, filters and pre-filters, which are fantastic for what we are doing (they don’t fog up goggles and are easy to breathe in, unlike some other masks we wear!).

Unfortunately, we are short of the pre-filter holders, which means that about a third of the respirators can’t be used.


There are absolutely no stocks anywhere in the UK that I could find (Arco supply them here and the lead time from Sundstrom is currently about 8 weeks). I wondered whether any of you fine people might have a spare holder in a drawer in your workshops? I appreciate that it is a cheeky ask and I apologise, but I’m a bit desperate and this, and buying a 3D printer are my last-ditch efforts.

If anyone did have a spare holder and was prepared to lend it to us, I would obviously pay postage and then replace it for a new one when stocks become available. You would also have the grateful thanks of a load of Northern bobbies :D

The image attached is one example, but there are other designs. It’s basically a plastic disc with a hole which holds the pre-filter in place. Thanks for reading.


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Could something like that be 3d printed? Might be an easier way of getting a quantity quickly.
Hi Marcros. Thanks for your reply. I’m sure that it could, but I have zero understanding of 3D printers, nor do I know anyone who has one who I could approach. In the normal run of things, I’d go to a company who does that...but then if this was normal I wouldn’t need the holder I suppose!
Is the pre-filter essential? Given the purpose the mask is being used for it won't make any difference, the pre-filter is used to stop bigger particles of sawdust from blocking the main filter. You are using it to stop virus particles (which are probably passing through the filter anyway) and will be changing the filter far more often than a woodworker would.
PM’d with 3D printing support options: the numbers you need are easily knocked out by a 3D printing supply house, the issue would be the design files and ensuring that they fit.
Rorschach - cheers. We discussed this and were told that the guidance has been worked out by boffins and that the pre-filters were essential for the respirator to function at the level it needs to. I think that the filters are not to stop virus passing through, but rather the aerosol droplets containing the virus. Hopefully this is based on some carefully worked out science :?

Alpha Dave - Thankyou. I’ll have a look at that now.

I appreciate the replies guys.
Hmmm sounds like a placebo to me.

Anyway, since the filters will be changed often, the pre-filter probably doesn't need a long lasting fitting. What about hot glue or double sided tape to hold the pre filter onto the front of the mask? Probably a better seal than those clips anyway, they aren't very tight.
The company that Alpha Dave put me in touch with are sounding promising in terms of 3D printing, so I’ll see where that goes.

We considered tape or glue, but I’m not happy that it would work effectively, or (as importantly) that my real would feel confident that it was working properly.
I use one of those masks but never had pre-filter on it. According to the Arco website the pre-filters just extend the life of the main filter by catching large particles. As far as I can tell it's just a 4" disc of polyester filter material so maybe you could get hold of some material and make your own.


• Protects the main filter from premature clogging by larger particles

CE Category 1




Designed to remove large particles the Sundström SR 221 Pre-filters are used to extend the life of the main filter. The SR 221 should always be used for particle, gas and combined filters.

For use with the Sundström SR 500 Powered Respirator, SR 200 Full Face Mask Respirator, SR 100, SR 90-3 and Freeflow Half Mask Respirators. Pre-filter holder SR 5153 secures and protects the pre-filter against handling damage. Also used for face-fit tests together with test disc SR 322.
Thanks Lofty. I thought the same thing, but the pointy-heads have come up with guidance about PPE which we have to stick to.
Noggsy":b034ntzz said:
Thanks Lofty. I thought the same thing, but the pointy-heads have come up with guidance about PPE which we have to stick to.
I've just re-read your original post, it's the holder you're after not the pre-filter, I think I might have one in the shed, if I have then you're welcome to it. Just been to look and I do have one for you if still required. That speed reading course could have been better. :D
Lofty, that would be amazing, thankyou. As per usual, we’ve got loads of the filters, but are short on the holders :)

I’ll PM you my details and thanks again.
It’s kind of been said before, but that part looks very simple and could be made by a fused deposition process very easily (3D printing in popular parlance) if you’ve got one to hand, a local university or technical college could have that modelled up in an hour and a bunch made overnight, or try any rapid prototyping house (afraid I don’t know any up north offhand and you’ve probably got more pressing matters to deal with)

I’d offer to help if I had access to that kind of kit anyone

You could always upgrade the filter, are you using the P3 filters. You can get filters specifically designed for organic compounds. The filters also attach to each other so you can have a p3 followed by a charcoal on. I do this to reduce the load on the expensive filter when spraying.
Im sure I have the part you want that retains the pre filter, where would you like it sent to
Wallace, thankyou so much, I will PM you.

Unfortunately, all PPE stocks everywhere are zero and there appears to be no imports for about 2 months. I’ve spoken to the people suggested above to look at 3D printing and they were positive, but have come back and said it is too expensive to to it for what it is, which I fully understand.

I’ll see if I can find a local firm and approach them.

Thanks again to everyone for your suggestions and particularly to Lofty and Wallace for their kind offers.

Stay safe.
Noggsy, There is a company that Peter Millard (OTP) got his 3d printer from, can't remember the name but if you pm him for it, they may be able to help
Also on the 3D printing front, if you google "hackspace [your nearest large town]", you will probably find a bunch of nerds with a closed hackspace itching to do something useful, and reverse engineering and printing some of these sounds like it would fit the bill.
Noggsy, I’m sorry if this is way out there and no use in practical terms for you and your team, but have you considered these?

I’ve nothing to do with the company but I’m aware of other agencies using them under standard respirators and standalone.

In any event, good luck with the 3D printing. I’ve no doubt they’ll sort you out.

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