Filter feature in question - Mail call: readers sound off

Tools of the Trade, Sept-Oct, 2003 by Leif Persson

I am writing about your article on gas cut-off saws in the July/August 2003 issue ("Diamonds in the Rough," page 50). Some of the article is well written and the opinions of the author are clearly stated to be nothing but that. But I think his preference for dry pre-filters and his statements about them are misleading to your readers. The reason the filters (consisting of an "open foam") are oiled on the Partner and the Multiquip units is because a dry foam filter is basically useless in filtering the fine dirt generated when cutting concrete. The cutting action from an abrasive blade generates large amounts of dust with a particle size of between 10 and 50 microns. A typical paper filter has a maximum hole size of approximately 10 microns, which is much more effective at stopping fine dirt.

The typical hole size in a foam filter is never smaller than about 300 microns. This means that a typical dry foam filter will not stop anything smaller than 300 microns. By applying oil to the filter surface, this type of filter becomes extremely effective, because the filter now "traps" the dirt and dust in the oil. An oiled filter can contain as much as 10 times its own weight of harmful dirt. One benefit to this is that the more expensive paper filter will last significantly longer without replacement.

Leif Persson

Technical Manager

Partner Industrial