On 5 July, 15:31, Tom wrote:
Hi All,

The instructions with this towel rad merely said use PTFE tape around
the tread of the value tail when screwing this into the rad.

But I can't stop it leaking (slow drip) - it purely replies on the
thread of the valve tail to keep it water tight - there is no flange
for the tail to but up onto. The blanking plug and bleed valve at the
top don't have this issue as they have rubber seals that sit between
them and the rad itself. this isn't possible with the valve tails.

I've tried leaking compound - no luck, it still leaks - slowly drips
actually.

Any suggestions as to what might solve this?

Thanks, Tom

The tail pipe is a British Standard Pipe thread. There are two sorts.
Tapered and parallel. Parallel threads are hard to seal with tape.
Tapered threads are designed for just this. The seal is formed ON THE
THREAD.
Assuming it is tapered, PTFE tape will do the job. However it has to
be wound on to the thread correctly. You wind the tape onto the
thread by rotating the threaded part IN THE DIRECTION YOU WOULD TURN
IT TO SCREW IT IN.
If you wind it on the other way, as you screw it in the tape is just
pushed off. Start at the thick end of the thread and finish at the
small end. There needs to be sufficient tape to completely bury the
thread, excess will be pushed off. You soon get to know how much to
put on. You will have to mess about to know how much to tighten it.
But less than you might think. Usually about one thread is left
showing when tight. But it varies. And may have been over tightened in
the past.

Parallel threads need some sort of a joint to seal them. Normally
there is a shoulder at the end of the thread. if you're clever with
the PTFE, you can form one by winding lots of tape on at the shoulder,
again applying the tape as described above.