Coupling vessel = Expansion vessel (EC010571)? What is an "Automatic Expansion Unit" (EC010269)?

Hello, I was wondering if EC010571, named "Coupling vessel", is also "expansion vessel" or if there is another class for "expansion vessel" (I haven't found it).

On the other hand, I'm trying to find more information about the function of an "Automatic Expansion Unit" (EC010269). For what I've seen, you basically connect it to an expansion vessel in order to maintain the pressure in the vessel, right? 

Thanks,

Roberto

The standard expansion vessel is EC010958 - Membrane pressure expansion vessel. I am not sure exactly how these coupling vessels work, the attached schema might give you some more idea. It is combining a base vessel with a coupling (or connecting?) vessel and involves a compressor?