Water from a vent pipe

Softus · 17 Jul 2006

doitall said:
That is the example I was trying to explain to Softus, probably not very well I should add.

The thing is, I grasped your explanation from the very beginning, but I disagreed with it, which isn't the same as not undestanding it.

It doesn't matter whether the pressure originates from inside or outside the cylinder unless the flow rate (from the fault) is so high that it exceeds the maximum flow rate up the cold feed, in which case it would be possible foe water to emerge from the vent first.

Invariably, split coils and faulty shower valves don't leak mains water quickly enough to force it out of the vent. ChrisR's case of a blockage in a basin tap outlet is a different case because an open basin tap valve will release mains cold at a relatively high flow rate.

Gasman1015 · 17 Jul 2006

Softus said:
Gasman1015 said:

Water tank overflowing, customer recently fitted bristan shower unequal pressures, mains backflowing into gravity hot water, cold water tank filling through hot water vent.

Click to expand...

Faulty valve, or was water coming out of the vent only when the shower was in use?

Not faulty, just rubbish.

The point is you were both correct and it merely depends on the where and at what pressure the mains was flowing.

They were not examples, real life.

doitall · 17 Jul 2006

Softus said:
It doesn't matter whether the pressure originates from inside or outside the cylinder unless the flow rate (from the fault) is so high that it exceeds the maximum flow rate up the cold feed, in which case it would be possible for water to emerge from the vent first.

Of course it matters, the resistance will always be less on the outside than the inside, and any pressure exceeding the head will take the easy route, e.g. the vent

Softus said:
Invariably, split coils and faulty shower valves don't leak mains water quickly enough to force it out of the vent. ChrisR's case of a blockage in a basin tap outlet is a different case because an open basin tap valve will release mains cold at a relatively high flow rate.

Some cheap mixer taps and blenders will backflow at a high flow rate, (any valve that mixes in the body ) CE marked taps have two parts in the spout and mix in atmosphere.

Softus · 17 Jul 2006

Gasman1015 said:
you were both correct

To be picky, I would say that we were both wrong - I was wrong in saying that water couldn't come out of the vent before rising up the cold feed and raising the cistern level, and doitall was wrong in saying the inverse of that.

However, the OP's problem clearly involves hot water being forced from the cylinder back into the cistern, because he said that the cistern water was warm. Even the full contents of the hot distribution pipework, plus the vent, wouldn't be enough to make an entire cistern "warm". I've had two of these (yes, in real life), and the nothing was emerging from the vent in either case.

Life would be much easier if Teggs would but return and report on progress.

Softus · 17 Jul 2006

doitall said:
...the resistance will always be less on the outside than the inside...

Not if the coil is split - an 450mm cylinder will offer far less resistance to the passage of water from the outlet than 22mm gauge pipework!

Gasman1015 · 17 Jul 2006

OK, I give up, carry on beating each other up.

Softus · 17 Jul 2006

doitall · 17 Jul 2006

Softus said:
doitall said:

...the resistance will always be less on the outside than the inside...

Click to expand...

Not if the coil is split - an 450mm cylinder will offer far less resistance to the passage of water from the outlet than 22mm gauge pipework!

The coil is inside the cylinder, not outside, therefore the pressure/head within will raise and the water can go up the cold feed or vent.

You cannot raise the pressure/head in the cylinder from outside, all the time you have a pipe to atmosphere.

Softus · 17 Jul 2006

doitall said:
The coil is inside the cylinder, not outside, therefore the pressure/head within will raise and the water can go up the cold feed or vent.

You cannot raise the pressure/head in the cylinder from outside, all the time you have a pipe to atmosphere.

I don't know why you think this, but it finally explains the basis of your misunderstanding. Do you think that inreasing the level of water in the CSC doesn't increase the pressure inside the cylinder?!

Pressure in a fluid acts in all directions equally.
Blaise Pascal, 1623-1662.

Therefore you can increase the pressure in the cylinder from the outside.

doitall · 17 Jul 2006

Softus said:
doitall said:

The coil is inside the cylinder, not outside, therefore the pressure/head within will raise and the water can go up the cold feed or vent.

You cannot raise the pressure/head in the cylinder from outside, all the time you have a pipe to atmosphere.

Click to expand...

I don't know why you think this, but it finally explains the basis of your misunderstanding. Do you think that inreasing the level of water in the CSC doesn't increase the pressure inside the cylinder?!

Therefore you can increase the pressure in the cylinder from the outside.

Of course it does

Increasing the height of water in the Cistern 75mm to the overflow will raise the pressure by 0.015bar. In your offline example, to increase the pressure 0.2bar you would need the cistern raising by 1m.

To increase the pressure say 1bar (mains) you would have to raise the cistern 10m, obviously you cannot raise the cistern or the vent, so you have more pressure/head in the pipework than the cistern, probably about 8m more as an average.

Pressure in a fluid acts in all directions equally.
Blaise Pascal, 1623-1662.

Only if the vessel is sealed on all sides. If you then make a hole in the top of the vessel the water will stay put, whereas if you make a hole in the bottom the water will run out.

For no water to exit the vent, the mains pressure backflow would have to be less than the height of the vent over the water level. Example.. add 0.2bar pressure the vent would need to be 1m higher than the cistern water level.

Lets say the OP vent was 300mm above the water level, to avoid water from exiting the vent, the maximum you could raise the pressure would be 0.060bar.

Does that clear it up for you

Softus · 17 Jul 2006

doitall said:
Softus said:

Do you think that inreasing the level of water in the CSC doesn't increase the pressure inside the cylinder?!

Therefore you can increase the pressure in the cylinder from the outside.

Click to expand...

Of course it does

OK - but it was worth checking that point.

I don't follow some of your maths in the following text:

Increasing the height of water in the Cistern 75mm to the overflow will raise the pressure by 0.015bar. In your offline example, to increase the pressure 0.2bar you would need the cistern raising by 1m.

The numbers should be 75mm == 0.0075 bar and 1m == 0.1 bar.

Pressure in a fluid acts in all directions equally.
Blaise Pascal, 1623-1662.

Click to expand...

Only if the vessel is sealed on all sides.

I fundamentally disagree. This is the very cornerstone of our amicable disagreement.

...Does that clear it up for you

Should I interpret the rolling eyes as a sign that you have a closed mind towards this and are convinced that I'm wrong?

No offense meant, but if we can't agree on the application of Pascal's Law then there's no earthly point in discussing any other aspect of this problem.

Agile · 17 Jul 2006

When Softus is not arguing with me he is doing the same thing with John or others.

He seems convinced that he gains some pleasure from that although I dont know what that can be.

There is a solution!

Suppose we ALL totally ignore all his cut and paste?

That includes you John!

Tony

Softus · 17 Jul 2006

Agile said:
When Softus is not arguing with me he is doing the same thing with John or others.

...or working, sleeping, gardening, watching TV, reading, doing the washing up, doing paperwork, fixing the car, going for a meal, in fact, tons of stuff that doesn't involve arguing. You have delusions of your own importance Agile.

He seems convinced that he gains some pleasure from that although I dont know what that can be.

Er, no, it's you who's convinced. You mischievous little troll

There is a solution!

Yeees, you could post your own view on the technical content of this topic?

Suppose we ALL totally ignore all his cut and paste?

Feel free. You've been ignoring me anyway. BTW, this post involved no cutting and pasting whatsoever. The real reason that my use of the quote feature irks you is because you don't understand how to use it yourself.

That includes you John!

Who the F is John?

doitall · 17 Jul 2006

Agile said:
When Softus is not arguing with me he is doing the same thing with John or others.

He seems convinced that he gains some pleasure from that although I dont know what that can be.

There is a solution!

Suppose we ALL totally ignore all his cut and paste?

That includes you John!

Tony

Now your being really silly Tony.

I have enjoyed our little chat with Softus, both on line and off, perhaps thats where people go wrong, they don't listen to other ideas/opinion.

Stop I wouldn't even think about it

Agile · 17 Jul 2006

Softus said:
Suppose we ALL totally ignore all his cut and paste?

Click to expand...

Feel free. You've been ignoring me anyway. BTW, this post involved no cutting and pasting whatsoever. The real reason that my use of the quote feature irks you is because you don't understand how to use it yourself.

Who the F is John?

zzzzzzz.....

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Water from a vent pipe

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