Mini Expansion Vessel

[Bollod]

First post since intro!
Worcester 28cdi in property when we bought. Worcester engineer when servicing says should have a mini expansion vessel in cold supply because a water meter is fitted. Boiler has worked with very few problems over the years so why is mini expansion vessel needed now? Always had a water meter and it is approx. 30 meters from boiler position.
Retired plumber friend says not needed because that length supply pipe gives plenty of expansion. (I understand the idea of hot water pushing back into cold supply)
However, since a liquid is not compressible how would it allow expansion.

Don't want to spend money unnecessarily so am asking for guidance

 

[townfanjon]

Yes Worcester want them , it will help protect the plastic block within the boiler , if the boilers had brass blocks they wouldnt really need them .

 

[Bollod]

Yes Worcester want them , it will help protect the plastic block within the boiler , if the boilers had brass blocks they wouldnt really need them .

Thanks for that, looks like I must bite the bullet!
Seems to me that with boiler manufacturers giving longer guarantees you have to jump through more hoops so not to give them any wriggle room to avoid paying out!

 

[Stanios]

Liquid is compressible your pressure gauge on the boiler should tell you that!

 

[Bollod]

Liquid is compressible your pressure gauge on the boiler should tell you that!

As a new member of the forum I am sorry but have to disagree. The pressure shown on the gauge is pressure exerted on the water in the sealed system, it does not actually compress the water.
If liquid were compressible hydraulics on a digger or the brakes on a car could not work!

 

[Stanios]

As a new member of the forum I am sorry but have to disagree. The pressure shown on the gauge is pressure exerted on the water in the sealed system, it does not actually compress the water.
If liquid were compressible hydraulics on a digger or the brakes on a car could not work!

Its fine to disagree!
I pressure test sections of pipes and radiators (no expansion vessel there) and can pump it up to 10 bar if I like, every stroke of my pump sends additional quantity of water into an already full sealed radiator compressing the watter. So from 1 bar to 10 bar I will deliver another 200ml of water. I can then cap a radiator that had 1 bar of pressure and another that had 10 bar and you will find the 10 bar radiator has more water.

 

[Bollod]

Fair point but would suggest that the rad had expanded slightly under the pressure to take the extra volume.
And my point about hydraulics still stands.

 

[AlexGas]

Liquid is compressible...

The answer is NO, one could compress water though, but only by a tiny smidge. It could be a long thread...

 

[Stanios]

The answer is NO, one could compress water though, but only by a tiny smidge. It could be a long thread...

You can compress any liquid apparently https://www.google.co.uk/search?q=c...1&ved=0ahUKEwiV1YSGvsbOAhUlP5oKHS58B58QvwUICg

 

[AlexGas]

You can compress any liquid apparently https://www.google.co.uk/search?q=c...1&ved=0ahUKEwiV1YSGvsbOAhUlP5oKHS58B58QvwUICg

The answer is yes, You can compress water, or almost any material. However, it requires a great deal of pressure to accomplish a little compression. For that reason, liquids and solids are sometimes referred to as being incompressible.