Pressure Vessel

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JohnTH

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OK, so this is not a small boat relater enquiry, however, there are so many practical folk on here that someone will be sure to have an idea.

My domestic hot water at the house is at mains water pressure. This is achieved by having a stainless steel tank within a tank of hot water that is heated by the central heating boiler. Now, given that water expands as it gets hot, there is a vent to atmosphere provided on the central heating side. An atmospheric vent is difficult to achieve on the domestic side so, a pressure vessel is provided to take the strain.

The question is this.

Are there different pressure vessels for central heating use (water is circulated round the system) and different ones for the mains pressure domestic hot water is changing?

The people at the merchants have absolutely no idea and phoning the manufacturer in Italy was difficult.

73s de
JohnTH
 
There does not seem to be any distinction between expansion vessels for sealed heating systems and non vented hot water systems although there is for other special uses

The size and pressure rating will have to be suitable for the system and the pressure thats all.

Take the non return valve out of the feed to the system and you wont need one any way :D
 
Expansion Vessel

Yes there are.

Generally expansion vessels for the CH system are Red in colour and those for 'potable' water, i.e. drinking (not that you would normally drink hot water!) are Blue. What the difference internally is I don't know but probably the materials are better to avoid contamination of the drinking water.

A good plumbers merchant should be able to advise a suitable replacement.
 
Thanks for that Vic, this confirms the limited amount of research that I have been able to do on the subject.

The size of my pressure vessel is 18L and the safe working pressure 4bar. I have not managed to measure the pressure of the cold water feed yet.

These questions arise after a failed pressure vessel back in July. It had been is service for just about a year. The merchant became extremely defensive regarding the quality of the vessel and its guarantee, “must be the wrong one for the job” said he.

Whatever the argument, the pressing need was to get the system back in service. The expedient fix was the same size vessel from a different manufacturer and merchant.

All has been well until I spied the same size vessel, but painted blue instead of red, as fitted in my system. Close questioning of the merchant selling the blue item produced an inconclusive answer. This is when the worm in my mind started wriggling and prompted this post.

Not sure if the water Company would be too pleased it I take the non return valve out though. The potential of all that “contaminated” water surging back into their supply pipes could just be the end of their universe!!

73s de

Johnth
 
Good morning Captain

The good merchants in Irvine had no idea what the difference between red and blue signified. Of course, if I had my wits about me this should have been obvious. Now that you have pointed it out, it is. Thanks!

88s de
Johnth
 
I think thats right about the materials, at least for the diaphragms, being different in those for potable water.
It did not register what the materials were but just noted that there was a difference. Presumably the ones on hot water systems have to be able to operate warm if not hot while those on drinking water systems only need to withstand cold water but must be of some nontoxic or food grade material.
 
A plumber is required to be certified or licensed to work on these pressure vessels. I'm not sure if DIY is allowed
 
Mains water pressure is sometimes a good deal higher than the domestic radiators will withstand. hence the pressure gauge and filling loop to ensure that the potable water doesn't become contaminated. Legionnaire's disease and so on.

Have you checked your mains pressure to ensure that it's below the 4bar rating of your accumulator or does your boiler incorporate a pressure regulator?
 
savageseadog said:
A plumber is required to be certified or licensed to work on these pressure vessels. I'm not sure if DIY is allowed
Click to expand...


It is same as Gas Safe for gas. LoL..... Precisely for the lack of knowledge of these systems as being made obvious here.

In the boiler world they call these thingies expansion bottles and unlike on boats accumulators is the name given to bigger ones which store heat not pressure. I take it you are talking about an expansion bottle.

Here are details of a good make and they seem to indicate that colour is indicative ove the type/size and not duty.

http://www.rwc.co.uk/public/expansion/xves-001.pdf
 
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Expansion vessels for fresh water are not made of ferrous metal, if you use the wrong type you will end up with rusty water from the hot tap eventually and the vessel wont last long (the water in your radiators is not continually replacing and should have inhibitor in it so not much oxygen)
There is normally a pressure reducer on the cold main before the cylinder usually set at 3 bar. There should also be a pressure blow off valve piped up to outside.
If the pressure vessel is under size or the pressure reducing valve is faulty water would be expelled from the pressure blow off valve.

Pete
 
What a mine of information there is on this site and the range of knowledge is phenomenal too.

Thanks, it looks like the pressure vessel that is installed in my hot water system is for central heating and should be for potable water. No, I don’t drink it but I do brush my teeth in it !

As for needing a certificate to work well, I have been certified so many times that
I have lost track and I have obtained more licences than I could not keep track of them either. So, I do not want any more of them. Any way, when I retired all my qualifications, licences and certificates went in the bin on the grounds that I hope that they will never ever be needed again.

Yes there is inhibitors in my radiators.

No I have no idea what the water pressure is...yet.

Thingies is an excellent name for the device that is installed, think I will stick with that bilgdiver and mant thanks for the link, excellent.


73s de
Johnth
 
Hi, you require, from any half decent plumbers merchant, an expansion vessel of 18ltrs volume, for mains pressure hot water cylinder. Make sure you are only getting the vessel, not all the control valves as well. It will probably be white, definitely not red. The white will be for potable water, hot or cold, and either coated inside or made of stainless steel. A flexible connection is usually used, for convenience. What is wrong with your existing vessel? if it is not working, the high pressure relief valve, normally 6bar will be dripping. To test, the schrader valve should release air when opened,if it does, it only needs to be pumped up, if water comes out then replacement required. To pump up, release pressure from system i e turn off the cold feed and open a hot tap, with foot pump, or electric, inflate to pressure indicated on label. If no label 1.5 bar is sufficient. As long as you do not alter the physical position of any of the brass ware you will be o k doing vessel changes or re-inflation. Finally, if you replace the vessel replace the flexible, if fitted, as well.
 
It will probably be white, definitely not red.
Click to expand...
Sure about that? I suppose you should be!

Looking at whats on offer red seems to be the colour for hot water, or heating systems while white is for potable water.
Blue is presumably for pressurised non potable cold water systems.

All rather confusing in some cases the colour seems to relate to the size rather than the application
 
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Hello Alruss

My hot water tank is 164L and works up to 10bar. Well, that is what is on the label. There is nothing wrong with the pressure vessel however, it is painted red and when I noticed another colour (blue)available it started a worm niggling in my mind, hence the original post.

Yes, my intention is to change to a potable item ASAP. Good point regarding control valves, I will watch out for this.

No, there is not a flexible connection it is hard wired to the 22mm hot water pipe from the tank.

73s de
Johnth
 
As said already, quite correctly, red is for a heating system, white is for potable water and is not going to give brown water at taps when you come back after a couple of weeks holiday.

A flexible connection is a good idea, especially if it has a ball-o-fix type valve in the flexible link, as you can turn off the valve, let off the water pressure in the expansion vessel by loosening the vessel end of the link (with bucket underneath to catch the water), and check the air pressure at the valve, pumping up if required.
 
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