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Pipe size for unvented system

Discussion in 'Plumbing and Central Heating' started by BuildingNovice, 30 Jul 2010.

  1. BuildingNovice

    BuildingNovice

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    We have an unvented cylinder with system boiler setup, and are finding that water flow in shower falls as basin taps are opened, which I understand should not be happening with a 'megaflow' type system.

    I've been told that one option to improve the water flow is to increase the pipe size coming into the property.

    My question is would this increased size need to go all the way to the cylinder (which would be a major job) or could it just be to the stopcock (which is more feasible) although then have you not just shifted the bottleneck location further up.

    Any advice appreciated.
     
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  3. Agile

    Agile

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    It all depends on where the main restriction is located.

    Thats usually in the pipe from the street to the house.

    Its normal to distribute up to the cylinder in 22 mm.

    It needs to have the input pressure at the cylinder measured and a graph drawn of pressure against flow rate.

    I assume this has always been the case since installation and that it has been regularly serviced.

    Tony
     
  4. BuildingNovice

    BuildingNovice

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    Thanks - I'll measure the pipes and report back
     
  5. Agile

    Agile

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    Its not the pipe sizes which are most important but the resistance as demonstrated by loss of pressure at the inlet as flow is taken.

    Tony
     
  6. BuildingNovice

    BuildingNovice

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    Thanks again Tony - there is a gauge next to the stopcock and near the cylinder - I will measure the readings and also the flow rate.
     
  7. BuildingNovice

    BuildingNovice

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    The mains pipe into the house is 15mm to the internal stopcock and then 20mm has been used for cylinder/boiler connections.

    The pressure gauge next to the stopcock is showing 2.5 bar (with no taps running).

    I'm not sure how to measure the water flow - presumably you put the tap on maximum?

    So, will changing the 15mm to 25mm and leaving the 20mm in place make any difference?
     
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  9. Agile

    Agile

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    You must give us the test information.

    To measure flow you time how long a bucket takes to fill and use simple maths to see how many litres per minute.

    Do it at 1/3, 2/3 and full on for a start. Measure flow rate and see the pressure on gauge at that flow rate.

    Tony
     
  10. Happyplumber

    Happyplumber

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    15 mm inlet from mains is not really good enough from experience ,this should have been noted by the installer and the pipework changed to the incoming mains for 25mm mdpe at least.

    This would have resolved the issue of flow ,I can see this problem continuing until the mains into the house are improved

    Sometimes a tiny drop of solder can cause major issues ,hey Tony!!!
     
  11. bengasman

    bengasman

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    Chain is as strong as the weakest link. In this case that means you need to upgrade the smallest pipe first, which probably means going back to the meter/streetvalve.
     
  12. Agile

    Agile

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    Until he has measured the pressure/flow we just dont know. For all we know it may be a blocked filter or a swollen tap washer!

    I am doing work at a property with a 1/2 supply and it gives 47 litres per minute open pipe at the bath.

    When the owner told me that at first I asked him to measure it again and give me all the figures. But he was right!

    Tony
     
  13. Happyplumber

    Happyplumber

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    You carry on measuring and doing calculations Tony,let the real plumbers tell you from experience,have you cleared the blockage you created,three visits at least now from my calcualtion,poor thing from 47 down to 6 litresoh how i wish all the general public could see your post to prove you competence that is hidden in the combustion chamber!
     
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