Testing an Expansion Vessel

[jaw]

When testing an expansion vessel, how much water should come out of the schrader valve when the centre pin is depressed for it to fail? A dribble or a full jet?

 

[SimonG]

Should have no water coming out of the valve, any water to me is a sign of failure.

 

[Dannypipe]

Me too. Though I heard on a manufacturers training course last year that a small amount of fluid could just be condensation within then confines of the dry side.

 

[jaw]

Thanks Simon, When the boiler is first put into heating mode the gauge shoots up to 3 bar before settling back down. The boiler then looses total pressure over about 24 hours (I have checked for leaks on the pipe system first - none found), would this also point to a faulty expansion vessel?

 

[Dannypipe]

Yes!!

You've just described the textbook example!!

 

[Best]

Is pressure relief valve discharging? Is the air charge on vessel correct? On the water point,- I think if pressurised air suddenly loses pressure, the air can lose it's water content. I may be talking rubbish, as it's just something I recall.

 

[jaw]

Thanks Danny, you've just confirmed what I thought

 

[Dannypipe]

Water heats up. Water expands by around 4%. Expansion vessel is ruptured and therefore has no room to accomidate expansion (its full of water), so a safety valve opens (pressure relief valve) and dumps the excess water outside. Then the system cools, the water contracts by 4% and your guage on the boiler drops.

Water can't compress, so you don't need to lose much to see this pressure drop.