Inflatable Life Jacket Bobbin / PFD (Personal Floatation Device). Replacement Yellow Bobbin is a replacement part for automatic inflators. When Yellow Bobbin gets wet it deploys the CO2 and vest inflates automatically. Must be replaced if Bobbin gets wet. Features: Replacement part for automatic inflators on life jackets or inflatable devices that use CO2 cartridges Bobbin dissolves when immersed in water and causes the CO2 cylinder to inflate the Personal Flotation Device Designed for recreational use, bobbins should be replaced every three years to avoid inadvertent inflation. Replace Annually for commercial use. Inspect and Replace if Life Jacket got wet. Long shelf life when kept in sealed packaging.