If you’re under the illusion that you have to change your lifejacket gas-bottle cylinder every year, you may be wrong. Examine it closely and you’ll see a ‘safe weight for operation’ in the small print on one end. Take it home and pop it on the kitchen scales. If it’s OK, blow up the lifers with your lungs to make sure they’re tight and leave them overnight. Then repack, and that’s it, done. Sometimes they last for years.