Expansion vessel stuffed, can I fit an 'external'(?) one?

[Agile]

I have never done it on that model but there is no reason why you should not fit an external EXV.

Doing that will even give an extra hot "instant" storage capacity.

You dont need to fit anything else as long as you are aware that the boiler isolating valves could be closed and isolate the protective devices in the boler.

To guard against that it would be necessary to fit a PRV close to the new EXV.

You should not fit an isolating valve in series with the new EXV ( although it does make maintenance so much easier and I would often fit a tool operated valve but its not correct ).

Tony

 

[bluefudge11]

Hi Tony
Thanks for the prompt response,

So if i understand correctly, the PRV on the boiler could get isolated if the the boiler valves are turned off. but how would the pressure then build up in the EXV to warrant (and crack) a seperate PRV ?

The tool operated isolation valve is a good idea (why is it not correct? is it legislation)

Thanks again
BF

 

[Agile]

I am happy to give you some free advice.

But I dont have time to give you training though!

If you cannot work it out for yourself and you think that all "plumbers" are ignorant and you dont want to believe what we say unless we give a detailed justification then obviously thats your choice!

Tony

 

[bluefudge11]

Hi Tony

I am not asking for training, I am just looking for advice, but if you don't have the answers then that' fine.
I am a fully qualified mechanical engineer so do understand a little about fluid dynamics, and so my logic is that if the boiler is isolated then how can it build up 3bar of pressure to crack a remote PRV.
There is know way i would suggest that plumbers are ignorant and that's the very reason i am seeking the advice from them.
Thanks

 

[Agile]

Hi Tony

I am not asking for training, I am just looking for advice, but if you don't have the answers then that' fine.

I am a fully qualified mechanical engineer so do understand a little about fluid dynamics, and so my logic is that if the boiler is isolated then how can it build up 3bar of pressure to crack a remote PRV.

Thanks

I know all the answers!

As a MIMechE eng I am surprised that you cannot work out such a simple senario!

Of course I am assuming that you have a filling loop on the heating side of the isolated boiler.

If that is the case then the filling valve could be left open or be leaking and the system pressure will increase to the highest mains water pressure and crack open the new EXV.

Two out of four attending a focus group on Tuesday lived/worked in areas where the water pressure was over 6 Bar and caused problems with most water devices like showers and float valves unless a pressure reducing valve was fitted.

I have seen three burst EXVs in the last three months!

Tony

 

[bluefudge11]

Thanks Tony - I now understand, This assumes that the boiler has been isolated and at the same time the filling valve is opened or leaks and that the filling loop is connected ?

Simple scenario yes but likely ....um

Better to be safe than sorry though
Thanks
BF

 

[BigBurner]

Hi Tony
Thanks for the prompt response,

So if i understand correctly, the PRV on the boiler could get isolated if the the boiler valves are turned off. but how would the pressure then build up in the EXV to warrant (and crack) a seperate PRV ?

The tool operated isolation valve is a good idea (why is it not correct? is it legislation)

Thanks again
BF

You are correct in your observations. If the boiler isolation valves are off, the PRV on the boiler will open...and you are right, there is no way there can be any pressure build up on the CH loop side. BTW, a pressure vessel is the last line of defence and is designed to blow if all else fails.

 

[BigBurner]

Thanks Tony - I now understand, This assumes that the boiler has been isolated and at the same time the filling valve is opened or leaks and that the filling loop is connected ?

Simple scenario yes but likely ....um

Exactly.

 

[bluefudge11]

Thanks for the advice Big Burner

 

[BigBurner]

Thanks for the advice Big Burner

BTW, the pressure loop has to be disconnected from the mains - regs. Many just have it in place and loose, so that if the valve passes it squirts out and not into the sealed CH system. So if the pressure loop is disconnected and some fool isolates the tool operated valves on both the flow and return on the boiler and starts it up, then the PRV on the boiler will open. Then you only have one mechanical safety device, the PRV. The expansion vessel is the backup which is on the other side of the isolation valve. Depending on the internal layout you may want to put in a second PRV in case.

With no connection to the mains there is no way there can be a pressure build up on the CH rads loop - unless a fool keep the pressure loop connected - if so the expansion vessel will then blow. However 6 bar is not blow your house up pressures.

 

[petit_pablo]

Do i need any seperate isolation or check valves ?

It will be fitted close to the boiler

It is a sealed system - using Baxi 105e combi

Thanks for any advice
BF

Do not fit any valves or isolations between the expansion vessel and the system.

 

[Soggy_weetabix]

To the OP,

Please please dont listen to any advice given by bigburner!

I have seen comments made by him today which... for want of a better word... are far from safe and uneducated.

He appears to gain information from a 'source' and advice wholly innapropriate actions that in a lot of cases could prove unsafe.

As a forum in general, a lot of us would prefer him banned, and the mods are watching him. Not closely enough as all todays drivel has been left for all to view.

Edit: If you read most posts, you will see bigburner disagree with every expert on here, but totally agree with anyone else.

Dave

 

[gas4you]

Totally ignore the incontinent Bigwaterdrivel. He knows nothing in the real world. Only what he can read in brochures or google on the net

The videos he points to are purposely set up to create a 'home video' and this has never happened on a correctly installed domestic unvented HW cylinder.

He is full of carp and has a chip on his shoulder against anyone who actually knows what he/she is talking about

 

[screech]

even if you were to replace the standard vessel i'd add an external one as well because the expansion vessel, due to the hot water store, is ridiculously small and if you have an average house with 8 rads (i know you have 7) you need an additional one, if you have less rads but they're big then you also need one.

if you can get away with fitting the external vessel i'd do that.

Depending on the internal layout you may want to put in a second PRV in case.

why? the standard pressure relief will still work

 

[BigBurner]

abuse deleted by mod 10