Learned something I thot I ought to share. The dry powder types will compact the powder into the bottom of the cannister during off road use. I was told that I should knock the powder loose at least once a year, possibly more often. Sure enough, the one Patch was SOLID. The powder won't come out when I need it to if it's clumped up solid. It took a lot of work to get the powder knocked loose w/o beating up the cannister. Last thing I want is for the cannister to fail b/c of a ding I put in it. I think I now understand why extinguisher's in commercial and industrial places need to be recharged once a year. It isn't b/c the CO2 leaks out. It's b/c the powder compacts into the bottom while just sitting there. I think mounting them nozzle down might help this situation. Then the powder would settle to the 'top' and turning it right side up will make it easier to knock loose. The better and easier solution is to buy a refillable and have it recharged at least once a year. I'm looking fwd to the Fire Fighting pro's comments on this topic. Hope to learn some more.