Vokera linea 28 Pressure drops and leaks

[godspeed2004]

Hi,

I know there are similar discussions on this subject already but i'm after some specifics if anyone can answer please.

My comb boiler pressure drops to zero in a day and the overflow pipe drips water.

So plumber left yesterday after pumping up the vessel and said if it leaks again (which it did this morning) then the vessel will need replacing...

My questions:

1. What is the purpose of an expansion vessel? Is it to control the amount of pressure in pipes while the water is boiling?

2.Someone on internet mentioned that pressure relief valve needs replacing (instead of expansion vessel), what is this?


Thanks

 

[jackthom]

When the water heats up it expands and the pressure in the closed system rises. The expansion vessel gives the expanded water somewhere to go without resulting in a dramatic increase in pressure.

If the vessel is faulty the water pressure will rise too far and a pressure release valve will let some of the hot water escape through the "overflow".

 

[godspeed2004]

Thanks Jack, I'm beginning to see the light... Could it also play in a part in helping the water pump to work, i'm thinking that if the hot water is being compressed by the vessel (the air bag pushing against it) it would push water through the pump more easily. I'm probably thinking too much into it!

 

[johnlogiebaird]

I think what can happen when the Expansion Vessel fails is:

The rubber membrane in the EV perishes/disintegrates over time. This leads to a loss in pressure in the system, perhaps because the air contain by the once intact memebrane escapes through the auto-bleed valve, or perhaps ends up in a radiator and gets bled out – either way your boiler will no longer be at the recommended pressure when cold (i.e. 1 Bar).

You re-pressurise the boiler to 1 Bar when it is cold. Happy days. Unfortunately, because there is no longer any ‘spring’ in the system provided by the air behind the membrane (i.e. lets assume where the once was air there is now only water), then any rise in pressure due to the water being heated is significant. If the pressure in the system is greater than 3 bars, the pressure safety valve will lift (as it is designed to do) and release pressure.

When the system cools again, you have lost fluid through the PSV so the cold pressure will be less than 1 Bar when cold and it will be very likely that the PSV will have debris in the valve seat from having opened and will no longer maintain pressure anyway.

The solution:

Replace the Expansion Vessel, if indeed it is faulty and replace the PSV – which is definitely faulty because you have confirmed there is fluid coming out of the pipe outside. Technically, it’s not faulty, it just isn’t closed properly. But it will have to be replaced. And it isn’t an overflow pipe. It’s more like a discharge pipe.


That’s my take on it anyway!

 

[johnlogiebaird]

Further to that, just re pumping-up or replacing the vessel will be a fruitless effort if the PSV isn't replace also.