valves

[druiaghtagh]

Anybody know the purpose of a double block and bleed valve please ?

[j2buttonsw]

If you are talking about plumbing then a double block valve is also known as a double check valve or a non-return valve. Its purpose to limit water to go in one direction only. They are commonly used for outside taps (I think there is a bylaw ensuring this) so any "infected" water -say from your hosepipe end being stuck in dog poo -cannot be drawn back to your drinking water tap supply. The bleed valve is a valve in a radiator that allows you to bleed any trapped air in it. It also may mean the drain cock which is a valve that allows you to drain water from your central heating sysem. If is not about plumbing then I am sorry for wasting your time.

[jenxxie]

Please see the answer as detailed in the previous question within this category :  --   the answer posted within THIS topic has slightly missed the point and DBB's are a little "beyond" domestic plumbing, where little check valves or double check valves are employed, purely as back-flow preventers,  stopping any mains contamination through back-syphonage.    The matter of air-eliminators or even AAV's on commercial / idustrial heating installations are something completely different amd nothing to do with double block and bleed.