Thread: Needle Felt bags

Bob,

Brief but good discussion on this issue here.

It's definitely worth cleaning them somehow even if it is just banging them on the side. I put my regular 30 micron bags through the washing machine about every 3rd empty. However, you should not do this with needlefelt as washing compacts the fibres and makes them less effective. Just shake them out as best you can.

Eventually they will compact and clog no matter how much you clean them and they will need to be replaced.

Cheers
Bob

Hi Bob,

I wouldn't do it.

The filter cake that forms on the bag aids in building up the prefiltering. By washing them, you're destroying the needlefelt and making larger holes in the bag (relatively speaking.)

Just tap it to knock out most of the dust, let it settle then take away the dust container for extraction.

All that's necessary.

Cheers,

eddie

Originally Posted by eddie the eagle

The filter cake that forms on the bag aids in building up the prefiltering. By washing them, you're destroying the needlefelt and making larger holes in the bag (relatively speaking.)

dust cake will improve filtering but also significantly reduce flow leaving more dust hanging in the workshop air for longer. Which is better is debatable. Better than any bag is removing the air and dust from the room altogether.

Just a clarification here. Washing doesn't destroy the needlefelt or make larger holes, if anything it makes smaller holes but the holes don't do the trapping anyway. Needlefelt is composed of a weave that contains millions of free ended fibres, which do the particle trapping. Washing collapses these free fibres and reduces filtering. Think of a bundle of cotton thread that has been snapped with frayed fibres splayed out like flower petals. Washing is like licking these fibres and drawing them close together. Compacting the free ended needlefelt fibres also reduces air flow. It's not like the air pathways are larges, more like there are less flower petals to tangle up the particles.

In a reverse sense, it is recommended that polyester fibre filled chainsaw chaps are washed regularly. The reason for this is so that the dirt can be removed so that the fibres can untangle and easily slide past each other when they are pulled out by the chain to jam stop the motor.

Hi Bob,

You appear to have some experience here.

I was going off the instructions and technical advice of DuPont and other filter bag manufacturers from the time when I used to have to look after about 140 baghouses, ranging in size from 2500m3/hr to 250000m3/hr (35cfm approx = 1m3). The suppliers explained it as I stated.

The dust collection is not collecting efficiently until the bag's loaded with a filter cake. A clean bag gives a higher airflow and allows a lot more dust/a lot larger dust particle through the filter.

There's no law to stop you from giving the bag a shake occasionally - they do this in industry automatically - if the bag's got too thick a filter cake built up on it and no air's getting through, give the supporting pole a rap. When you do this, you'll get some idea of the state of the filter bag as well. It shouldn't allow too much dust into the atmosphere.

My impression of the cheapie dust collectors is that they're designed to run for 5-10 minutes, and when you stop them, the bag collapsing dislodges the accumulated filter cake.
Cheers,

eddie.

(who gave up on a filter bag and went to a pleated cartridge filter for home use.)

Hi Eddie,

I have about 35 years of experience but mostly at the sub-micron HEPA end of the game (hospital theatre grade or better) where filter capacity is not an issue and filters can last for 7 to 10 years before needing to be replaced. The reason they can do this is prefiltering is done using either needlefelt or more recently H-type media which we use extensively.

You are right needlefelt bags are designed to filter better after they have a layer of filtered cake on them. However they cannot do this indefinitely and after a while they will clog up and at least some cake needs to be taken off somehow or other.

We stopped using needlefelt about 15 years ago and moved to a roll type multilayered media which can be washed. However, this is only good for a about 5 microns but will protect a HEPA from the bulk of the chunky components allowing the HEPA to do it's job without getting too clogged.

Same your pennies and replace the bags with pleted filters

Originally Posted by China

Same your pennies and replace the bags with pleted filters

I agree, I have one of those and wouldn't go back to the bag.

Some good food for thought and thanks for the responses.

- BobL - thanks for the link to "Woodweb".

For the moment I'll probably go with just giving it a beating while I check out the pleated filters etc - the quick look I had means that I'm looking at some fairly serious $$$. The bag replacement for the filter idea may be determined by the timeline for shifting my DE to its own little cubby outside of the shed.

Regards,
Bob

Originally Posted by Bob38S

The bag replacement for the filter idea may be determined by the timeline for shifting my DE to its own little cubby outside of the shed.

Bob - if you shift to an outside cubby then I would just stay with the needlefelt. I use 30 micron cloth bags on my dusty in it's outside cubby. I used clear polycarbonate sheeting as cubby cladding because the cubby is out of sight behind the shed. I would have thought there would have been some visible signs of dust on the polyC but apart from the 1 mm of dust per year that accumulates on the paving bricks that act as a floor and a fine layer on the DE itself, the cladding is remarkably clean. I reckon the reason for this is the very fine dust is carried away by the breezes and diluted into the atmosphere.

Cheers

Originally Posted by BobL

Bob - if you shift to an outside cubby then I would just stay with the needlefelt. I use 30 micron cloth bags on my dusty in it's outside cubby. I used clear polycarbonate sheeting as cubby cladding because the cubby is out of sight behind the shed. I would have thought there would have been some visible signs of dust on the polyC but apart from the 1 mm of dust per year that accumulates on the paving bricks that act as a floor and a fine layer on the DE itself, the cladding is remarkably clean. I reckon the reason for this is the very fine dust is carried away by the breezes and diluted into the atmosphere.

Cheers

Sounds good to me Thanks.