to weld or not to weld

[wese]

im fitting a new overflow pipe which is the pipe for the cold storage and f&e cistern,

what i want to know is ,does this want solvent welding on any joins

thanks

 

[Nige F]

YES...definitely. And 2 pipes...one for each tank. They make a lot of mess if they leak into the house, found a couple like it over the years.

 

[wese]

thanks for that,both tanks are sharing one overflow pipe,so i guess i better advise the customer to get two fitted instead

 

[ChrisR]

There are two systems of overflow in common use - one is pushfit, one is welded. And they're slightly different sizes!

 

[chrishutt]

Can anyone explain why the two overflow pipes should be kept separate? I can't see any objection to joining them together providing the junction is below the level of both tank connections.

 

[doitall]

Can anyone explain why the two overflow pipes should be kept separate? I can't see any objection to joining them together providing the junction is below the level of both tank connections.

No problem with a shared overflow if the size is increased.

maybe a slight problem identifying which is running without unwrapping both tanks

 

[chrishutt]

Why should the size of the overflow pipe be increased if serving more than one tank? It's very unlikely that both tanks will overflow at full rate simultaneously (same principle as both pressure/temperature relief valve outlets on an unvented cylinder joining together in 15mm).

As for telling which tank is overflowing, I've seen groups of up to 4 separate overflow pipes emerging at low level from a building, with no indication as to which floor/tank each serves. Why not join them together?

 

[doitall]

Why should the size of the overflow pipe be increased if serving more than one tank? It's very unlikely that both tanks will overflow at full rate simultaneously (same principle as both pressure/temperature relief valve outlets on an unvented cylinder joining together in 15mm).

As for telling which tank is overflowing, I've seen groups of up to 4 separate overflow pipes emerging at low level from a building, with no indication as to which floor/tank each serves. Why not join them together?

One has to assume they will both run at the same time.

Interesting comment on the unvented, I assume you don't have the ticket, because you're wrong big time.

 

[chrishutt]

I do have the "unvented ticket".

Typically the temperature relief valve and the pressure relief valve each have 1/2" outlets. The 15mm discharge pipes from these join to form a short, combined 15mm discharge pipe as far as the tundish. Beyond the tundish the discharge pipe increases to 22mm (or more if required by length of run).

If the combined discharge pipe (above the tundish) was sized to take full flow from both valves simultaneously, it would need to be 22mm rather than 15mm. Building regulations and manufacturers appear to think this unnecessary because it is extremely unlikely that both temperature and pressure relief valves will function at the same time.

 

[doitall]

I've seen lots of things in my travels it dont make it right though.

Discharge should be at least the next size up as you say. most need to be 28mm.

bregs G3

table 1 is handy

 

[chrishutt]

I'm referring to the discharge pipe above/before the tundish, not the pipe below/after the tundish. If you check some manufacturer's instructions (e.g. Vaillant Vantage) via the web you should be able to see the relevant detail drawing.

 

[doitall]

I'm referring to the discharge pipe above/before the tundish, not the pipe below/after the tundish. If you check some manufacturer's instructions (e.g. Vaillant Vantage) via the web you should be able to see the relevant detail drawing.

I'm aware of what you mean Chrishutt, but the critical point is where the water hits the atmosphere i.e. the tundish, at this point water under pressure converts to gravity.

Anyway I still wouldn't connect two overflows together in the 22mm pipe