What is this called?

Can anyone tell me what this part is called? Cant find anywhere that sells anything that looks similar. I know it's linked to brake servo and is some sort of non return valve but if anyone has a part number be much appreciated.

The tape is covering a small hole which has been caused by the throttle cable rubbing on it. Its stopping the leak but not ideal.

 

It's a non return valve, or one way valve. Brendon Moss in Dubstock or similar should have them.

 

It's a non return valve, or one way valve. Brendon Moss in Dubstock or similar should have them.

 

Ah great. It's basically crumbling away. Is that part number for the little cap or the complete valve? I assumed it was all one piece as it is so brittle didn't want to mess about with until I'm sure I could get another one!

 

The cap just the pops on. You could replace it with a bit of blocked up vac line if you were stuck.