how does this danfoss drain off tail piece work?

[leaky_pipes]

I'm changing all my rad valves to danfoss and wish to add a drain off to a couple of them.

I bought this drain off tailpiece which sits between the rad and the valve, but for the life of me I can't see how it works!

It has what looks like a white button on the top, before purchase I though this was to open the drain off - but it doesn't move at all. Looking inside there is a vertical metal bar between the white 'button' and the drain off on the bottom.

I just can't work out how to open the drain off on the bottom.

Many thanks!

 

[cross thread]

White cap flicks out ,standard air bleed key will then fit.check the valve thread is same as a danfoss

 

[leaky_pipes]

yes, just discovered that myself!

thanks for the reply