It seems to act as a flow limiter in the one direction , which is when the pedal is being released., and also a damper to stop vibration being passed back through to the clutch. First car I have ever had with one on.
I have noticed before that if you depress the clutch fully and then let it release by sliding your foot off it the rate it comes back up at is not that fast.
Certainly compared to other cars I have had. It's located under the servo on the bottom of the plenum chamber so not easy to get to.
If you look down past the vacuum pipe on the front of the brake servo you can see it.
The one end of this is fairly close to the clutch master cylinder which is plastic, as a single connector isn't as long as the the damper that's being replaced and there doesn't look like a lot of give in the pipe I don't want to put any strain on the master cylinder joint.
Thus I have ordered two 10mm female connectors and two male connectors
BNP21 and BNP22 from this seller
http://www.ebay.co.uk/itm/281021660609
The idea is to put a male connector between two females and make a longer connector. That way there won't be any strain put on the joint hopefully.
To get at the damper to replace it I will remove the aluminium heat shield at the back of the turbo. Not that difficult to get it out and will give plenty of room to get at the part.