HEPA Filter Gel Seal Failure 1

[friartuck]

Hi Folks

I've just had 11 terminal HEPA filters out of 16 FAIL on a DOP test. The filters seem OK but the gel seal seems to fail.

The gel is about 14mm deep and the knife edge seems to seat into it ok...but there is leakage around the edges of the filter.

we can't understand it and neither can the filter box manufacturer.

Has anyone else had this problem.??

The filters are 99.999% at 0.3 microns and the HEPA's are H14 type.

The filters have been adjusted,raised,lowered, rotated and
everything else we can think of. We have fitted them with a small amount of gel seal (i.e with the knife sitting into the gel by about 5mm and we have tried full depth tightening where the knife site the whole 12-14mm into the gel...but still we get a leak around the edges???

Your assistance would be appreciated.


Friar Tuck of Sherwood

 

[Whoops]

"Has anyone else had this problem?"

No, not me.

Are you sure it's the gel seal that is letting-by? Is the knife edge continuously welded to the HEPA filter housing? Are the HEPA filter housings new, or is this a new batch of HEPA filters? Have the terminal housings passed the DOP tests with a previous batch of HEPA filters?

 

[friartuck]

Whoops

New installation
New filters
(I have used these before and they have been ok)
All filters have been scan tested prior to delivery
All terminal filter housings have been pressure tested prior to delivery

Confused

So am I

Are there different grades of gel?? The stuff we have is 'tacky' and appears to deform when depressed with a credit card but the gel forms a convex shape and does not appear to 'smooth' around the 'knife'. Perhaps we have a bad batch of gel???



Re-testing tomorrow

Let you know what happens



Friar Tuck of Sherwood

 

[Whoops]

I think I'd be looking at the filter housings, the knife seal may be distorted. I believe the HEPA filters are individually tested but I've been dropped in it several times by the contractors procuring cheapo, non-approved plant.

The filter housings may have been pressure tested, but this may mean the housing doesn't leak, rather than the knife seal doesn't leak. The housing might also have distorted during installation.

Are there different grades of gel??

Yes, I believe so. I think most of it originates from Dow Corning, but have only had one involvement with it. The stuff I had was a 2 part mixture, I think (long time ago). It also had a 'use by' date. Poor mixing or out-of-date gel might cause problems. I think that the gel must have performed properly when the filter was tested.

 

[friartuck]

Update

Job done. All filters passed. Reason........

a. Faulty batch of HEPA filters (It was stated that they had been scan tested?????????). I believe 16 out of 25 were 'bad'. The seal between the filter media and the aluminium frame had come undone. (We await an official report)

b. The odd filter frame had a leak. The knife edge was 'pop rivetted' onto the main filter terminal box and it would appear that the sealant between had somehow failed. The reason is unclear.

Again we await a report from the manufacturer.

Thanks for the help.

Ciao

Friar Tuck of Sherwood

 

[Whoops]

Thanks for the feedback, it's uncommon.

I find it surprising & worrying that 60% of the new 'tested' HEPAS were faulty and some of the new HEPA housings. The moral is to test after installation or it probably won't work as intended. The only time I've seen something similar was due to damaged media, which was probably due to rough handling during or after delivery.