HW Vent pipe

[Scott_1979]

hello, can the hw vent pipe basically come across the top of the cwsc and then angle back in at the top? Roughly about 30mm above the top of the cistern. All the other ones I have seen come way over in an elaborate way then back in. I have looked through all the plumbing books I have nvq etc, and also went through the water regs with nothing noted about this.

Also if it does need to come way over then back in can someone give me the reason why this needs to be? Thanks !

 

[jldplumb]

hello, can the hw vent pipe basically come across the top of the cwsc and then angle back in at the top? Roughly about 30mm above the top of the cistern. All the other ones I have seen come way over in an elaborate way then back in. I have looked through all the plumbing books I have nvq etc, and also went through the water regs with nothing noted about this.

Also if it does need to come way over then back in can someone give me the reason why this needs to be? Thanks !

to accomadate expansion without circulating water back into the cwsc, it needs to be something like 150mm plus 40mm for every metre of head of water between tank and cylinder ,also should have compression elbow before going into the tank (bylaw 32)

 

[Scott_1979]

ok any chance you know where that info is? Its ok if you don't! Was just curious as to why they always go up way higher than the cold water cistern then drop in, as opposed to just dropping in at a lower level, obviously providing the vent is long enough to take expansion as per your measurements. If you understand what I mean?? the first bend of the vent pipe is say 30mm above the cistern and goes in if room is tight.

 

[gassafe]

I guess the main tank of water takes up the expansion...

You could extend it if needs be, or leave if its been like it for years & causing no problems?

 

[plumben]

ok any chance you know where that info is? Its ok if you don't! Was just curious as to why they always go up way higher than the cold water cistern then drop in, as opposed to just dropping in at a lower level, obviously providing the vent is long enough to take expansion as per your measurements. If you understand what I mean?? the first bend of the vent pipe is say 30mm above the cistern and goes in if room is tight.

As said you need 150mm +40mm for every meter of head to the cylinder to take up the expansion and stop water from spilling over

 

[Best]

I believe the reason the vent pipe needs a lot higher is the water when heated will expand higher up a pipe than the cold water tank and could potentially keep spewing hot water into cold tank. If this process kept going for hours - the whole cold tank could end up with boiling water in it.
This happened in a couple of different homes in UK, that I know of and 2 people died. Immersions were left on and perhaps faulty stats, hence why new regs mean the stat in immersion must have a manually resetable built in cut out.
I know the findings with one of them stated that the vent pipe needs a proper height.

 

[jldplumb]

I believe the reason the vent pipe needs a lot higher is the water when heated will expand higher up a pipe than the cold water tank and could potentially keep spewing hot water into cold tank. If this process kept going for hours - the whole cold tank could end up with boiling water in it.
This happened in a couple of different homes in UK, that I know of and 2 people died. Immersions were left on and perhaps faulty stats, hence why new regs mean the stat in immersion must have a manually resetable built in cut out.
I know the findings with one of them stated that the vent pipe needs a proper height.

I went to a job the other where something similar had happened- the old immersion heater had been accidentaly left on for a few weeks, gone haywire and started expanded over then melted the ball float of the ball cock and flooded the place. Scary stuff!

 

[rocketmanbkk]

The vent pipe should rise 450mm above the cwsc.

One measurement that I remember from college!

 

[jldplumb]

The vent pipe should rise 450mm above the cwsc.

One measurement that I remember from college!

no thats the f&e tank, cwsc vent is the measurement above.

 

[rocketmanbkk]

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[rocketmanbkk]

Sorry didn't copy!

 

[rocketmanbkk]

Getting the book out!