In static systems, the transmission line is pressurized by a hand pump, or some other means, and the pressurization source is removed. Transmission lines are not hermetically sealed and will eventually lose pressure in static systems. Therefore, they require periodic recharging. Advantages include portability and simplicity. Disadvantages include requiring manual regeneration of the desiccant, and low purge and low system volume.
Dynamic systems incorporate a pressurizing source that provides dry gas on demand.
The source may be nitrogen tanks with a regulator or an automatic dehydrator. The source is permanently connected to the transmission line system and recharges it as required. Nitrogen tanks are mainly used on small tight systems and where mains power is not available. Advantages include a dew point lower than dehydrated air, no power requirements, no moving parts and inexpensive gas. Figure I. Return loss of a length of 3-inch air dielectric cable before and after the introduction of as little as 3ccs to 4ccs of water.