Recharging potable water expansion vessel

[Matt887]

I'm g3 register just wanted to check when recharging a vessel on a invented cylinder to 3 bar, as long as the diagram isn't at fault I only need to open a hot tap to drain system and leave open when I test the pressure and recharge there need to remove the vessel

 

[Johntheo5]

If the bottom of the EV is above the top of the UVC, shut cold water supply to the UVC, open hot tap to depressurise, break and disconnect the outlet from the EV, re pressurise, (pre charge) to 2.8bar. If bottom of UV below top of UVC carry out similar procedure until HW stops draining, then break EV outlet and drain the UVC until water stops flowing from the EV, then disconnect and re pressurise, as above.

 

[Matt887]

Thanks it's the expansion vessel is above the uvc. And tap is open. Do you definitely need to disconnect from the cold supply to truly get the correct reading. Or would opening the tap be enough

 

[Johntheo5]

Disconnecting at the EV confirms that there is no water in the EV but reasonably OK to assume if not disconnected.

 

[polesapart]

I only need to open a hot tap to drain system and leave open when I test the pressure and recharge

Yes, simple as.

 

[Matt887]

Thanks and then the pressure reliefs are they abit pot look whether they reseal after the EV reset? PRVs on boilers can be an issue do to sludge etc stopping them from resealing.

 

[Madrab]

Not so much on a potable water cylinder - given they tend to be nice and clean.

Older ones may be a bit twitchy as the rubber seals can harden over time stuck on the seat. Most expansion PRV's are on the cold inlet so aren't subject to much in the way of heat that can also cause problems - the T&PRV's can be a bit temperamental sometimes though as they do get hotter, usually cycling them a number of times can get them to sit back down properly, If they haven't done so after a number of tries then it's time to replace.

 

[robinbanks]

Regards the EV, if it’s been sat a which in a depressurised state the membrane may be stuck to the inside of the vessel, and getting it unstuck might take a while/bit of work depending on what pump you’re using.

 

[Johntheo5]

Regards the EV, if it’s been sat a which in a depressurised state the membrane may be stuck to the inside of the vessel, and getting it unstuck might take a while/bit of work depending on what pump you’re using.

There are two types of membranes, one, which seems to be more used on larger capacity EVs as used say on UVCs is sandwitched in the "middle", the other is a like a baloon and just shoved in through a flange on the water end, often wondered why this type doesn't be noisy as when the EV is precharged this baloon must be jumbled up against the water end, also surely decreases the effective capacity of the EV, not a big deal though if you size to 10% of vessel capacity or next size up. Does anyone just replace thes type if they fail rather than the whole EV, but probably not a great idea since there may be corrosion of the EV itself, over time, at the air end.