Spec of hose for expansion vessel

[marineb0y]

I need to replace a hose to an expansion vessel for an unvented cylinder. What should the spec of this be? The correct size tap connector is rated at 15 bar and 70deg C. Is 70 deg C enough?

 

[dcawkwell]

Copper pipe. Never used a flexible hose on one yet.

 

[Kev F]

Most flexi hoses from any good plumber shop will do, fitted hundreds like it, many get supplied with hoses, might struggle to get one of the longer ones though

 

[Boilerman2]

Any Flexible hose must be WRAS approved

 

[marineb0y]

thanks
The cylinder was supplied without one when it should have done, howeve i got it £300 cheaper from wolsey as it had no box (bargain!) and it has taken me 3 months to get around to fitting it so cant really go back and complain.

What does the WRAS stand for. Just scanning though a catalogue, some are specified as WRAS however they are oly 300mm long and i need a 900mm (or atleast 700mm one). If needs be, i can extend the connection in copper and just fit a small 300mm flexible.

 

[Dan Robinson]

You installed an unvented cylinder - and don't know what WRAS is?


Great.

 

[marineb0y]

Its not exactly difficult.
Is this another rant at the diyer.
I have had to replumb the entire house to do it (was going to anyway)
Didnt really need to know what WRAS was until i needed a hose that should have been provided. I could have just gone out and bought a WRAS hose but i was being intererest in knowing what implications it had

 

[Dan Robinson]

Rant? Where?

Hope you tell LBC though. It will need signing off.

I hope also you followed the instructions with regards the D1 & D2 pipe to the letter.

Have you seen one of these blow?

Rocket science it ain't. But a potential rocket it is.

 

[Paul Hield]

Surely the reason for using WRAS hose is concern over the growth of micro-organisms tainting water or even supporting the growth of Legionella. This is why it must be used for drinking water and other uses which might expose the user to atomised Legionella spray such as showers. I can see no reason why it is necessary for a central heating application where the temperature would kill Legionella and the risk of spray is minimal.

There is absolutely no connection between WRAS hose and the risk of explosion, that is controlled by the pressure release valve and in any case for a boiler to explode it would have to exceed the boiling point of water. If a component was weak it would just leak not explode. WRAS is about water quality not strength. This is just unhelpful scare mongering by so called "professionals" trying to put off DIYers.

 

[bernardgreen]

This is just unhelpful scare mongering by so called "professionals" trying to put off DIYers.

No it is NOT scaremongering.

If the water over heats and goes above boiling point ( it can go above 100°C when under pressure ) you have a critical situation. Hopefully the pressure relief and or over temperature valve will operate and release the pressure safely. When super heater water leaves the pressurised system and enters free air it instantly turns into scalding hot water vapour. Before it condenses to steam the vapour is invisible and extremely hazardous. The volume of the vapour is about 1500 times the volume of water that created it.

If you are not sure what sort of hose ( or pipe ) to use between the unvented cylinder and the expanasion vessel you probably don't have the necessary information about pressure relief valves and other essential safety devices.


I am not a professional. I have DIY plumbed two houses but I would not DIY an unvented cylinder.

 

[Paul Hield]

You are absolutely right that the system could explode if it overheated well above 100 degrees. But for that to be a problem two things have to fail: the thermostat and the pressure relief valve. A system without a functioning pressure relief valve is dangerous. That has nothing to do with the subject of the type of hose used to connect to the expansion vessel or indeed the presence of a expansion vessel. If your thermostat and pressure relief valve have both failed the expansion vessel will only absorb a small volume of the high pressure steam, it cannot prevent the pressure build up, that is not its purpose and cannot prevent the system failing somewhere under the excess pressure of superheated steam. Most likely the system will spring a leak in an inconvenient place and damage some fabric, it could vent superheated steam which is extremely dangerous and will tear your flesh off. But the expansion vessel plays no part whatever in preventing this other than delaying it for a few minutes.

The expansion vessel is purely for the practical purpose of stopping the loss of water through the pressure relief valve when water is heated and expands, it is not a safety feature.

 

[Dan Robinson]

it is not a safety feature.

Really

 

[gasmanstu72]

The expansion vessel is purely for the practical purpose of stopping the loss of water through the pressure relief valve when water is heated and expands, it is not a safety feature.

clueless ...

 

[AL66]

3 -4 years ago I was in work one Saturday afternoon in a plush central London office building, no one else in on my floor. Went to use the facilities (well away from where I was on the floor), found water gushing out under the door. Eventually manged to find someone with keys to get into the service cupboard, found an unvented cylinder fed with probably 35mm (it was big) copper mains - there was a hole in the pressure vessel you could put your fist through (with water flowing out like a river) . It had blown along the seam. Come Monday morning the building manager seemed pretty unconcerned - didn't seem to grasp the gravity of this event or the fact it probably pointed directly at their incompetence in not having the system serviced correctly.

For domestic, I believe this is supposed to be done annually (makes sense to combine it with the boiler service, etc) - is there any requirement for the same in commercial premises? If there isn't, there should be.

Would be interested on opinions on what the failure mechanism here was - failure of at least two safety critical components. Perhaps the pressure vessel is itself a last crude fail-safe in that it will rupture before the main cylinder?

 

[AL66]

Surely the reason for using WRAS hose is concern over the growth of micro-organisms tainting water or even supporting the growth of Legionella. This is why it must be used for drinking water and other uses which might expose the user to atomised Legionella spray such as showers. I can see no reason why it is necessary for a central heating application where the temperature would kill Legionella and the risk of spray is minimal.

There is absolutely no connection between WRAS hose and the risk of explosion, that is controlled by the pressure release valve and in any case for a boiler to explode it would have to exceed the boiling point of water. If a component was weak it would just leak not explode. WRAS is about water quality not strength. This is just unhelpful scare mongering by so called "professionals" trying to put off DIYers.

+ Why did you bother digging up a 3 1/2 year old thread??