Expansion Vessel in Unvented Cylinder Lost Pressure

[Maurice]

Hi
I've got a 12ltr Zilmet Expansion Vessel on a 170ltr Ferroli unvented hot water cylinder. It has lost pressure and as a consequence the pressure valve is venting water to the outside. I am assuming the problem is caused by a split in the diaphram as I cannot repressurise the expansion vessel. What concerns me is that the vessel was only fitted in November 2009 and was a replacement for the original expansion vessel that was on the cylinder when it was installed in March 2008 which suffered from the same problem. Is there another issue I am missing which could be causing this repeated problem or is it just bad luck?

 

[SimonG]

Is it a red Zilmet?

 

[Maurice]

No it is white and according to the label it is a 110-Ultra-Pro

 

[diamondgas]

Hi Maurice, wouldn't a split in the diaphragm give you water at the schrader valve? Where permitting with unvented I like to remove them to re-pressurise coz they take some pumpin up!!

 

[tackleburger]

It will re-pressurise whether split or not in theory. What are you using to do it? If it was split you would get water shooting out when you press the valve if that doesn't happen you need to pressurise it to 3bar.

 

[gassafe]

12 litre expansion for 170 litres of hot water..?? Is that big enough!?? All the un-vented i have fittted have been 18 litres i thought.

 

[Maurice]

I tried to re-pressurise the expansion vessel with a foot pump. When I pump it the pressure needle rises but then just sinks back to zero. When I attach a pressure gauge to the valve nothing happens (i.e. it reads zero). If I just press the valve in nothing happens. No sound of air being released, certainly no water.

 

[Maurice]

Wouldn't know how to safely remove the expansion vessel. I have attached a pressure gauge to the valve - it reads zero. Tried to pump it up using a foot pump, nothing happens. Tried pushing the valve in but no sound of air escaping and no water. Am at a bit of a loss as to what could be going on.

 

[tamz]

It is impossible to repressureise the vessel in situ unless the cylinder has been partly drained. The vessel needs to empty (it will be full of water) as it is being pumped up. It takes a lot of pumping. Think how long it would take you to pump up a car tyre with a foot pump. It is just about the same with this. Maybe best to get someone in to do it for you.
Unvented cylinders should have a service check done annually where this would be done if required.
Unfortunately most never are.

 

[fuzzy]

i have added new pressure vessels to systems before now. if you got somewhere you can put one on and its easier than removing the old one just add it and leave old one n place

 

[diamondgas]

Yep a lot LOT of pumping!!
If the diaphragm is fully deflated you'll need to pump out the water and then start to re-pressurise. I was once told that they should be re-pressurised with nitrogen, I don't know how true that is? As long as you're not getting water out the valve Maurice there's a good chance the diaphragm is still intact!

 

[GrahamM]

Ideally, I would get it fully checked by a qualified person.
The ex vessel needs to be checked if its burst or if the schrader valve is passing then the cylinder would need to be drained, the ex vessel re-charged, the cylinder re-filled and then fully tested.

12 litre expansion for 170 litres of hot water..?? Is that big enough!?? All the un-vented i have fittted have been 18 litres i thought.

The 12L vessel would normally suffice for a 170L cylinder in an average house.

Yep a lot LOT of pumping!!
If the diaphragm is fully deflated you'll need to pump out the water and then start to re-pressurise. I was once told that they should be re-pressurised with nitrogen, I don't know how true that is? As long as you're not getting water out the valve Maurice there's a good chance the diaphragm is still intact!

Ideally nitrogen would be better over air, but it is too expensive an option. It holds pressure a lot longer as it is a bigger molecule. Air also contains water so over time may cause corrosion internally.