I never intended to throw the debate so wide open. Clearly the opinion is mixed. So as the person who asked the original question, here's my humble opinion...
Compression joints are very unlikely to leak ever if made on properly wilth compound. Ballafix valves do weep from the slot (branch) quite reguarly, but you are talking about cheap valves manufactured 8 years ago. Most modern, full bore valves are of a superb qualilty and the price £4.50 a go reflects this fact.
I posed the question as I didn't want to go against regulations, but it seems I'm not.
The jury is still out as to whether I should do it or not, but we all recognise that it's a short cut and somtimes shortcuts pay off big time. The system I'm working on has three other plumbers working on it, and when one of them drained the system, I jumped at the chance to alter my pipework and but in the valves as it means I don't have to vent, inject inhibitor and take any flack from the client.
Finally to who ever asked, I can't hold the system on a vacuum as it is pressurised, and yes I could have applied a freeze, but I generally do that as a last resort.
Thanks to everyone for their opinion, I've read them all with interest, and I think they're all totally valid.
