I don't think that somebody will be interested but, anyway....
As you have seen, I'm using "Pre-Filter" on my shop vacs and it stops almost all the course and fine dust from reaching the main filters.
The problem was that, after a "good" working day, the pre-filter was clogging.....still I had good suction because of the large filter area but to get maximum performance, and I had to clean it (wash it) every day.
So I made a "Hammer" to "Bang" the pre-filter every now and then and by that, getting almost clean filter and maximum performance of the vac all the time without the need to open and clean, till it gets full.
Because the hammer drops down, it gives me also an indication when the barrel is full...if it doesn't return to its original position.
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