There are a few things to keep in mind when deciding whether or not to replace your cylinder inflatable PFD. First, check the expiration date on the CO2 cartridge. If it has expired, or is close to expiring, it's time for a new one. Second, inspect the fabric and materials for signs of wear and tear. If there are any rips, holes, or other damage, it's time to replace the PFD. Finally, make sure that all of the buckles and straps are in good condition and working properly. If not, it's time for a new PFD.