Vented / unvented cylinders, pros and cons

Discussion in 'Plumbing and Central Heating' started by bernardgreen, 20 Mar 2016.

  1. bernardgreen

    bernardgreen

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    The pros and cons of vented and unvented hot water supply are being discussed in depth on another forum.

    This is a reasonably good explanantion of the differences that was quoted.

    http://www.gasapplianceguide.co.uk/Mains_Pressure_Hot_Water_Systems.htm

    When describing the safety requirements of the unvented system it doesn't give much information as to what can happen if the pressure limiting valve becomes defective and allows the water pressure to rise above the setting of the cylinder's pressure relief valve setting.

    A pressure regulating valve did fail to control pressure and the results of that failure were the reason for the discussion starting on the other forum.
     
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  3. 75pete

    75pete

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    Could always have two PRV
     
  4. Dan Robinson

    Dan Robinson

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    ??
     
  5. Dan Robinson

    Dan Robinson

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    Is there a direction or question here or are you just propagating your dislike for direct fed systems?
     
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  6. bernardgreen

    bernardgreen

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    Yes there is a question. If the pressure regulator on the incoming mains supply fails and allows water at more than 4 bar pressure into the unvented tank what will happen ?.

    It will be interesting :-

    1/ to see the replies that are posted here and compare them with the opinions posted on the other forum.
    2/ to see if anyone here mentions the sort of event that prompted the discussion on the other forum


    [QUOTE="Dan Robinson, post: 3610808, member: 57625"or are you just propagating your dislike for direct fed systems?[/QUOTE]

    I do not dislike them, they have a place but given the need for regular test and inspection of the safety devices I feel they should not be installed without due consideration of the home owner's commitment to ensure they receive the necessary routine servicing.
     
  7. Dan Robinson

    Dan Robinson

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    One of the two safety valves will open. But not at 4 bar.

    Most cylinders I deal with are rated to 8 to 10 bar IIRC. The expansion vessel will absorb most of the rise, then the expansion relief valve will open.
     
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  8. bernardgreen

    bernardgreen

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    expansion or pressure relief ?

    And then when it does open what happens next ?
     
  9. Dan Robinson

    Dan Robinson

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    Water is released.
     
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  11. muggles

    muggles

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    When a pressure relief valve opens, what generally happens is that excess pressure is relieved, thereby protecting the appliance.
     
  12. Several fail safes in place, all though I've come across a few with one one or 2 that still functioned ok.

    Best I found was an ariston 210ltr with just a 7bar 90° T&P relief valve. No expansion vessel, no inlet limiting valve no 4/5/6bar prv. Only a valve on outlet and no drain point.
    That lasted 8 years with no problems until boiler broke down and they Started to use the immersion for a couple of days the T&P relief valve opened, so when I returned with the boiler part they asked me to have a look at the cyl as well :eek:
     
  13. Bye as long as installed correctly, there is no disadvantage to unvented. Quite a few advantages over open vented
     
  14. Dan Robinson

    Dan Robinson

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    I'm almost interested enough to ask for a link to this other forum. But ultimately I don't give schit.
     
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  15. PullerGas

    PullerGas

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    I do not dislike them, they have a place but given the need for regular test and inspection of the safety devices I feel they should not be installed without due consideration of the home owner's commitment to ensure they receive the necessary routine servicing.[/QUOTE]

    But all unvented cylinders must be annually serviced by a fully qualified Plumber with a G3 ticket. So you don't need to concern yourself fella, us pros have it sorted!!
     
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  16. bernardgreen

    bernardgreen

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    What process is used to ensure that this annual service occurs. ? Do "professionals" with G3 have right of entry to carry out the service even if the owner refuses to allow access to the cylinder ?
     
  17. PullerGas

    PullerGas

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    Eh no!! If the punter don't bother their arze getting it serviced & it takes out the gable end of their house who gives a feck!! Customers are like a bus to good tradesmen, you lose one another one will be along shortly......(y)
     
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