Is this a pressure relief valve?

[rec]

We have a Mega Flow system and today I noticed a small brass valve at the top of a warm pipe that appears to have been leaking. It's currently dry and there's no sign of any real damage but the staining would indicate it's been like this for a while. Is this normal? And should the valve be tightened up or left a little loose?

Many thanks in advance to anyone that can shed some light.

https://drive.google.com/file/d/0B_qEKHTZ4FrOdnF6UU1RZFE2RXc/view?usp=drivesdk

 

[Stadan20]

No it's an automatic air valve ( Aav )also should be left loose but it will probs leak if you do that , requires a replacement

 

[andytw]

Its an Automatic Air Vent. They have a limited life as they get crudded up and fail. I changed 2 yesterday for my neighbour on his heating system.
You may need a certificated plumber to work on you Megaflow. Others on here will tell you.

 

[rec]

Thanks very much. Is there any danger of a serious leak from these? Might take a few days to get someone out.

 

[andytw]

It's probably been like it for a long time. They just tend to dribble.

 

[ianmcd]

It's probably been like it for a long time. They just tend to dribble.

A bit like Tony Agile, it will dribble but nothing to worry about