re: science question

21 Sep 2004
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United Kingdom
Dear reader,
Can anyone explain the science behind the following situation i encountered?

The feed pipe from header tank to inlet on an indirect cylinder is very corroded with visible holes. If I shut the gate valve that stops the feed from header tank the pipe from valve to bottom of tank doesn't leak. shouldnt the weight of water in tank back up that pipe as it has holes in it? Even if i cut the pipe below the valve no water leaks out, can anyone explain why? Does that mean I can cut very close to inlet in tank and it still not pour out? Thanks for all those a lot cleverer than me out there.....which is probably most of you!
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maybe cold inlet at cylinder base is clogged solid with limescale?
s hawking
I take it the valve is higher than the top of the cylinder. Water will always level itself so you can keep cutting the feed pipe untill you get to the same level as the top of the cylinder before the water from the cylinder starts to come back out the feed pipe, so no you cant cut as close to the bottom of the cylinder as you wish without a flood occuring. The leaks stop because the cylinder obtains its pressure from the header tank, isolating that brings the pressure right down. A fairly accurate guide is that for every 10mts of head hight = 1 bar water pressure. Have I understood and answered your question? If not then I too am just as confused.
good point, are the holes in feed pipe above the level of outlet of cylinder?
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The vent pipe should also be full of water up to the level of the water in the header tank.

If you cut pipes full of water and nothing comes out, there's a blockage.
What are the symptoms of the plumbing and central heating problem that you need help in solving?

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