We have 3 of these filters on our 100k gal pool. They have a screw on cap (about 10 in diameter) with a pressure gauge on top of the cap. I've been fighting a losing battle with one of the caps and I'm looking for any tricks to get it off. I've broken one of the plastic wrenches that fits over the fins on the cap. I've tried getting more leverage with a length of pipe on the wrench handle. I've tapped on the cap with a rubber mallet, scraped around the rim, applied various lubricants. It's stuck and I'm stuck. Any ideas? Thanks. --Fred