I built my dust collection system a couple of years ago, 1.75 HP Powermatic motor, fan etc. and Onieda cyclone, .5 micron Wynn filter, 5" ductwork throughout. I have a small shop so runs are not long. I found and installed a magnahelic meter that measures in inches of water (pressure) and plumbed that into my filter. After almoust two years it has slowly crept up in pressure and am now reading about .6-.7 inches of water. I have not blown out the filter yet since I put all this together and it all seems to be running fine. My question is for magnahelic and Wynn filter users, at what point (inches of water) do you blow out the dust from your filter? Randy