The UML MK5 Automatic system activates when the cartridge comes into contact with water. The cartridge mechanism contains a compressed high powered spring which is held by a cellulose paper element. When the paper element comes into contact with water it dissolves and releases the spring which pushes a cutter forward to pierce the CO2 cylinder and release the CO2 gas. The gas then travels through the one way valve in the inflator head and inflates the lifejacket.
The Automatic system is backed up by a manual override, which allows the user to pull the toggle and activate the cutter to pierce the gas cylinder in order to inflate the lifejacket alternatively.