Fire extinguisher CO types have the test information stamped on the cylinder, all other types get a sticker on the back of the cylinder. Once dry, the units are recharged. Unlike the UK, the US does not rebuild extinguishers and replace valves at specific intervals unless parts are found to be defective, with the exception of halon. Halon types are often given new o-rings and valve stems at every internal maintenance to minimize any leakage potential. OEM equipment must be used for replacement parts for the extinguisher to maintain its UL rating. If parts are unavailable, replacement is recommended, keep in mind
Cold gas thruster movement and activating the extinguisher. Because the gas is usually unheated, speed at the throat is low and very low performance is achieved; in a vacuum with nitrogen gas a specific impulse of 73 seconds can be achieved. The maximum theoretical specific impulse for nitrogen gas is 76 seconds. In the simplest approximation, the specific impulse is modeled as proportional to the square root of the (absolute) gas temperature, so performance rises as the gas temperature is increased. A thruster in which the performance is increased by heating the gas by an electrical resistance is known as a resistojet. Cold