'83 240D automatic 219k miles

Going through my vacuum system (hoses, ck valves, etc.). A few questions:
What is the purpose/function of the green "dashpot" (as I've seen it called) that comes off of the VCV?
Is it a restrictor, as opposed to a check valve?
Should it pass air in either direction?
Do they "wear out" and is there a way to determine that it's not functioning properly?
And, lastly, can it be installed in either direction?

Thanks, in advance.