Drain valve in vertical cooper pipe

[markyyyyyy]

May seem a bit silly question, but is it okay to install a brass drain valve on a vertical copper pipe (using a T piece) that goes into a radiator valve?

Or do I need to install it on the horizontal pipe run before the vertical?

 

[gas112]

its perfectly ok to do this

 

[Madrab]

Only thing I would point out is that you would not be able to drain any pipework below the drain off, if that was the lowest drain point.