Domestic expansion vessels and HSG274 Part 2

[Raver]

Hi guys,

Quick practical question, I work in the control of Legionella industry as a consultant my background is microbiology and I am fairly limited in terms of practical plumbing skills. The new guidance on controlling the risk in domestic hot and cold water systems (HSG274 Part 2) suggests that expansion vessels should be purged. May of my clients accept this but frequently ask ok how do I purge these vessels and I never know what to say....any advice on how this is done?
Thanks in advance

 

[solutions]

If purge means simply empty the vessel of water then issolate the water if its an unvented hot water cylinder vessel. Then drain off sufficient water to allow the membrane full of air to squeeze out the water. Too be totally sure you would probably have to remove the vessel and also depressurise the precharged air/gas bladder.
I have seen reference to expansion vessels with 2 water connections intended to permit the water to circulate through the vessel during expansion, combating stagnation and the cultivation of legionella. rather than just remain captive however I have never seen one.

 

[Subby]

Am I correct in thinking expansion vessels in unvented hot water systems should be fitted vertically with the inlet at the bottom to prevent stagnation / microbial growth? That is what I've been instructed on commercial jobs.

 

[Ermintrude]

That's how we fit them.

Wouldn't see how discharging it will help? It's steel and rubber, the rubber is filled with water, the pores in the rubber won't be cleansed by emptying and refilling. Also in purging your going to be vaporising the spores - creating a massive risk. It's a bit like asbestos best left un disturbed. If by a miracle the system under pressurised then the dirty water will be heated in the unvented to over 60c thus rendering bacteria.

But to purge turn stop tap almost off. Open kitchen cold should be a trickle. Open bath tap - to allow air into unvented to prevent cylinder collapse due to syphoning. Run off hot tap with a cloth over it so the outlet dribbles along cloth and controls vapour generation. As hot water runs off expansion vessel will be emptied because of the 3 bar in shell, so upside down, left right or even on the moon it will empty . Reverse process and vessel fills with clean cold water

 

[tamz]

Btw this is a good one to get into.....ie legionella. Changing regs effecting landlords....money for nothing and your chicks for free :wink:

 

[Best]

Btw this is a good one to get into.....ie legionella. Changing regs effecting landlords....money for nothing and your chicks for free :wink:

...or you could be in Dire Straits! :smile:

 

[tamz]

Dire Straits - Money For Nothing - YouTube
Worst live band i ever saw. Dire :lol:

 

[Best]

Try this piece of Laura Cox playing Money for Nothing. For some reason she does it better. My eyes just won't stay on the guitar. :smile:
http://m.youtube.com/watch?v=LRiuhCsxHLs

 

[tamz]

I think i could sustain a bit of tremolo from her. I noticed in the passing she has nice blue finger nails :smile:

 

[chris watkins]

3/4" FBSP - Anti-Legionella Valve for Expansion Vessels

It is all about maintaining chlorinated water in the vessel, so that there is not chance of stagnation within the vessel.
The above valve encourages this but on domestic systems simple installing the vessel with the cold feed running by as close as possible i.e. no dead leg, would do the trick so long as the vessel charge is correct. The natural flexing with expansion & contraction as well as pressure changes in the system with fittings being open or shut, should ensure water movement in & out.

This does not apply to vessels in closed / primary systems.

 

[PhoenixServices]

I think i could sustain a bit of tremolo from her. I noticed in the passing she has nice blue finger nails :smile:

I can't say I noticed the nail varnish first.

 

[kris]

Hi Raver and welcome to the forum mate, good to see a professor of water biology in da house , does the name mean you used to have white gloves n glow sticks lol

 

[Killy Bing]

Tell them to have flow through expansion vessels...

 

[lame plumber]

I would be more interested to be shown how many cases of legionnaires have been traced back to expansion vessels being the primary cause. Then and only then would I consider the whole scenario worthwhile. Only saying as none of my customers with unvented cyls have suffered from legionnaires yet.