When should you replace the CO2 cylinder in and inflatable PFD?

You should replace the CO2 cylinder in an inflatable PFD (Personal Flotation Device) if it has been used to inflate the device, as it cannot be reused. Additionally, inspect the cylinder regularly for any signs of damage, corrosion, or leakage. If the cylinder is outdated or shows any signs of wear, it should also be replaced to ensure proper functionality and safety. Always refer to the manufacturer's guidelines for specific replacement intervals and recommendations.