Bleeding a hot water expansion tank.

[kayak]

Hi all.

 

I'm calling on your collective experiance one more! Hopefully this Saturday, after a miriad of setbacks, I should finally fill the water tank and prime the domestic water for the first time. Fingers are crossed that there are no leaks but my main concern is bleeding the the system.

 

I think im ok with bleeding the main cold system and i was going to do this first by turning the pump on (its a sensormax pump so there is no accumulator) with the cold taps open and turn them off one at a time when each stops pushing air. (so far so good?)

 

Now comes the bit im unsure about. After the outlet from the pump the feed split and goes through a non return valve and then through the calorifiers. After the calorifiers before the hot water makes its way to the hot taps i have put an expansion tank.

 

As this has no actual outlet and is tee'd into the system, how do i bled it? I have tee'd it into the system with a braided hose so there is a bit of movement and i can take it out of the bracket whist it is still plumbed in, so as daft as it seems im wondering if it should be put in upside down (with the air valve at the bottom)

 

I can see i've rambled but hope someone can tell me if im on the right lines and also how to bleed the expansion tank.

 

Many thanks.

 

Kayak.

[springy]

I can only presume that your "expansion tank" is functionally the same as an

accumulator i.e. a vessel with a rubber bladder dividing it into two compartments -

water one side and air on the other - in which case AIUI provided the air side

is pressurised before you turn the pump on then it will not need bleeding - when

the water side is un pressurised the bladder will be forced into the "water end" of

the vessel. There are several threads on here explaining the correct way to set the

pressure. (cant find it just at the moment)

 

springy

[alan_fincher]

I think Springy's explanation is correct.

 

If the expansion tank is pre-pressurised on the "air" side, it should have very little air in it on the "water" side, before you start watering the system.

 

But I can't see it matters if a small amount of air from the pipework ends up on the "water" side of the bladder. It will still be doing it's required job, whichever side of the bladder it is.

[kayak]

Thanks both for that, it makes sence. I wasn't thinking that the air side would be fully pressurised! I sort of imagined a sheet of rubber suspended halfway across the tank. Great stuff.

 

However, Its got me thinking about the pressure that should be in it. Seeing as its a sensormax pump that doesnt need an accumulator this tank is just for taking up the expansion when the water gets hot. So, what sort of pressure should it be charged to. I would think that it should be above the cut off pressure but below the blow off pressure for the PRV on the calorifiers?

 

Have i got it about right?

 

Kayak.

[kayak]

not wishing to waste anyones time, ive found a post that i started that was all about pressures so i'll re-read that. Just goes to show how long these bloody boats take to build!!

[springy]

<snip> I would think that it should be above the cut off pressure but below the blow off pressure for the PRV on the calorifiers?

<snip>

 

 

Sounds about right to me

 

springy