using bungs to change rad valve All aspects of plumbing questions and answers, help, tips and information

[bobplum]

id like to pick everyones brains
late last night had to change a rad valve on a radiator in a hallway decided to bung the outlet feed from the fe tank and the expansion pipe,normally i would drain but decided to have a change,to let the water out and pressurize the system i opened the bleed valve quite a bit came out,i then closed the bleed valve loosened the nut on the feed pipe to the valve i was going to change seemed ok then i slackened the nut on the rad tail and the water just kept coming and coming,under control but at no point did it create this vacumn i ended up draing the whole rad,so can anyone tell me were i went wrong
and dont tell me i went wrong by doing it late last night i had no option,long story and im tired and grumpy now
love you all
bob

[plumbbob]

Hey Bob, we all have days like that. 4.15 this afternoon. Last joint under bath. everything else gone really well today. Turned water on. Fountain. Flood. Panic. Mop up. Dry joint. Can't reach. Won't drain. Swear. Hit with hammer etc. Cry. Sound familiar?

Personally, I have had mixed results with the bungs. Don't use them very often.

Whilst they may stop the system from emptying because of the vacuum, I wouldn't expect it to include the rad you are working on simply because as soon as you undo the valve nut, air would enter allowing the water to escape. Does that seem reasonable?

[chris_on_tour2002]

obviously air is getting in somewhere - or is already in there. did u bleed all rads first? any trapped air in the rads would have been compressed to some extent and would have potential energy to release.

just a thought.

[Steve the gas]

Its early so I'm half asleep but I presume you put a bung on the vent pipe.............. Awaits shouting!!

[bobplum]

thank you everyone so far
i think im going to stick to the simplest form and that is if its drained then you cant go wrong until that is when you refill but as we all know thats a another story
keep up the good work everyone
bob