At the back of an atmos clock there is a bellow filled with ethyl chloride gas, the bellow expands and contracts with the changes of temperature or changes are atmospheric pressure. The in-and-out movement of the bellows keeps the mechanism wound up.
Because of the complexities of the Atmos clock, an Atmos needs a complete mechanical overhaul whenever serviced. An Atmos keeping good time does not need any periodic maintenance. Once an Atmos clock starts stopping it generally means that it needs a Clean and an overhaul, very little amounts of dirt will bring your atmos clock to a stop.