On Sunday, May 25, 2014 11:47:41 AM UTC+1, wrote:
Hello



I wonder if anyone can answer a plumbing question. I just changed the potable water expansion tank for my unvented water system. All seems to be working fine, but I am wondering if I have a missed a step.



I have a zilmet 24l tank pre-charged to 50 psi sitting at the highest point in the system.*Obviously the tank was full of air when I first connect it up and I am wondering if *I need to bleed the air from the water side of the membrane to fill it up with water? There seems to be no way to do it, and no suggestion it should be done, so I will presumably just contract legionaire's shortly?



Any comments appreciated!



Thanks

Darren

I understood the question.
I wouldn't bother.
The air (on the water side of the membrane) will just act as an additional expansion device, similar to the air trapped in a pressure gauge syphon tube.

The oxygen will dissolve and get carried out by the water.
The remaining nitrogen will gradually get entrained if/when the water speed exceeds 2 ft/s or so.
It doesn't do any harm and I can't see any need to remove it.
There's lots of dissolved oxygen in the mains water anyway. Some will come out of solution when the pressure drops, after the PRV set and refill the pipes anyway.