Soil stack air admittance valves, permitted position, and types?

Discussion in 'Plumbers' Talk' started by always_learning, Nov 19, 2005.

  1. always_learning

    always_learning New Member

    Can someone throw some light on this please....?

    Why (apart from the 'Regs'!) must an AAV be positioned above the flood level of the highest appliance?

    I have seen advertised an AAV that claimed to be a Type 1, or A, or B, or something?? which stated that it did NOT need to be installed above the highest flood level.

    I understand what AAVs do, and how they do it, but not the relationship to the flood levels.....? :)

    Any info will be gratefully received.

    Thanks
     
  2. harlowboy

    harlowboy New Member

    aav's or durgo valves should as far as i can remember terminate at a minimum of 1 mt aboe the spillover point of the highest appliance, normally a hand basin.
     
    simpo likes this.
  3. always_learning

    always_learning New Member

    Harlowboy,

    thanks, I know that they are supposed to terminate higher than the flood level, but the question is WHY? :) do you know...?

    :) cheers
     
  4. saint dave

    saint dave New Member

    Have a little think about it, where will the water go if their is a blockage further down the line.
    Answers on a postcard!!!!!!!!!!!! :)
     
  5. Dreadnaught Heating

    Dreadnaught Heating New Member

    An 'AAV' is an Air Admittance Valve, i.e, to let air in to the top of the system (therefore alleviating negative pressure zones in that system, which may cause syphonage of water in traps - phew). But you knew that anyway......

    So, as its name suggests, it lets air in, but is not designed to stop liquids getting out. Hence the need for it be well above 'high tide mark'.

    Hope that helps.
     
  6. doitall

    doitall New Member

    Very good sk the second part of your answer is not correct as the valve seals against smells etc getting out.

    Your answer it fits on the end of the run usually the highest point to enable air to be drawn into the stack to prevent syphonage.

    it could equally be installed on the end of a long run from a bath for example, or a stub stack both below the flood level
     
  7. always_learning

    always_learning New Member

    scalexkid,

    Thanks for your input.... :) I appreciate that it is not supposed to let liquids out.... so it is above the flood level of the highest appliance in order for a hypothetical flood to 'escape' through a lower appliance; bath , wc, bidet etc etc...?

    Is that right?

    Thanks again :)
     
  8. doitall

    doitall New Member

    scalexkid,

    Thanks for your input.... :) I appreciate that it is
    not supposed to let liquids out.... so it is above
    the flood level of the highest appliance in order for
    a hypothetical flood to 'escape' through a lower
    appliance; bath , wc, bidet etc etc...?

    Is that right?

    Thanks again :)

    No not right.

    It's to allow air to be drawn into the stack/waste pipe, if it was fitted say before a wc it would blow not suck, and as the valve is the non-return type design it wouldn't work
     
  9. always_learning

    always_learning New Member

    Doitall,
    I understand that the AAVs purpose is to allow the stack to 'suck' in air when the there is a depression in the stack, rather than suck water out of the traps.....

    ..... but this still doesn't explain why they have to positioned higher than the flood level of a the highest appliance, normally the basin.....It is not a case of before or after on the stack, rather above or below.....?

    thanks
     
  10. doitall

    doitall New Member

    Bit a luck I aint got much hair :)

    It has to be after the highest outlet or it will blow not suck.

    for example 2 toilets 1 upstairs 1 downstairs, you fit the aav between the 2, lower toilet will suck air in and the upstairs 1 ?????????
     
  11. always_learning

    always_learning New Member

    Doitall,

    Thanks for your input, but maybe you don't understand what i was asking, the AAVs that i have fitted are one way valves, they only allow air to enter the stack, no air is allowed to escape.......

    .... in your scenario are you saying as the upstairs toilet flushes it pressurises the stack below it...?

    cheers
     
  12. Dreadnaught Heating

    Dreadnaught Heating New Member

    Dear Always Learning
    I stand by my orignal definition of what it does and why........
    I quote from the manufacturers
    The Durgo valve is designed to reduce the number of ventilating pipes and subsequent roof penetrations in domestic, commercial and public buildings. Suitable for use in sanitary pipework systems up to ten storeys high, the valve must be fitted in a vertical position above the flood level of the highest appliance connecting to the stack. Valves should be installed within the building in a ventilated duct or roof space where there is no risk of freezing and must be accessible for inspection and testing.

    The 50, 82 and 110mm size valves have been assessed by the British Board of Agrément and awarded Certificate No 97/3427 which permits their use in accordance with the Building Regulations. A copy of the full certificate is available and provides comprehensive information on their use and installation.

    http://www.marleyplumbinganddrainage.com/swdesign.asp#r

    I reckon as they probably earn more than me, they must therefore know more than me.

    As with any other thing in life, follow the instructions.

    I don't know, or particulary bother how this blasted computer thingy works, I just read the book that comes with it........ :)
     
  13. doitall

    doitall New Member

    Doitall,

    Thanks for your input, but maybe you don't understand
    what i was asking, the AAVs that i have fitted are
    one way valves, they only allow air to enter the
    stack, no air is allowed to escape......
    .... in your scenario are you saying as the upstairs
    toilet flushes it pressurises the stack below it...?
    cheers

    I know exactly what your asking, as you say they only allow air in, so they have to be fitted on the end of the run to allow air to follow the plug of water that bombing down the pipe.

    Yes in my scenario no air could be drawn into the stack so it would try to push the water out of the lower pan, a good example of this is when the bath guggles when you flush the wc.

    As a test get a length of 15mm pipe and fill it with water holding your finger on the one end, turn the pipe upside down and the water will stay in the pipe until you let air in
     
  14. always_learning

    always_learning New Member

    Doitall,

    Thanks for the explanation, I think we will have to differ on this one, I don't want to waste any more bandwith.
     
  15. MechEng

    MechEng New Member

    This is interesting as I asked the exact same question a while back, again with no absolutely conclusive answer.

    So i've bought the durgo and fitted it in my planned location before fitting all the bathroom furniture as an experiment to see if it's working properly.

    It is well above the WC, but below the level of the sink overflow by a few inches. Has to be at this height to it can sit below the planned worktop level.

    Fitted it at the weekend, and put an inflated plastic bag over the valve and flushed the bog and emptied the sink.
    The bag deflated, which appears to show that all is working OK. Plus there is no loss of any trap seals.

    So I still don't understand the requirement that it must be above the highest flood level, and wonder if it's a "belt & braces" guideline to cover all possible circumstances?
     
  16. Hombre

    Hombre New Member

    Thinking this one through I'm pretty sure that the reason is a good old 'belt and braces'. If your Durgo is in the loft (where you can't see it) and you get a blockage in your pipework you really wouldn't want the loft filling up with cr*p whenever you flushed...
    At least if it's the sink or bog that back up you see the effect straight away...

    As long as the Durgo is at the highest part of the system it will never be the first point to overflow, so you are safe. I assume that the margin is an allowance made to overcome the effect of the head of water in U-bends etc.

    In your case MechEng you shouldn't have a problem unless you get a blockage somewhere that stops your sink water going down the stack, but won't let it flow into the toilet pan. This would probably need two blockages, and would probably be almost impossible to achieve in practice!
     
  17. always_learning

    always_learning New Member

    MechEng

    :) I have been in a similar position to yourself a few times now.......

    I have fitted AAVs above wc & below basin, below WC and basin, all varieties of position, and they always work...!

    Like you i tested them, with a plastic bag gaffer taped round the stack over the AAV.
    I have seen advertised AAVs that stipulate that they do NOT have to be above the flood level of the highest appliance, but as for why, well who knows..... :)

    The analogy of a pipe sealed at the end holding in a column of liquid is not a relevant one, that is to do with surface tension of the liquid.
    Any way, good luck..... Thanks for your input.
     
  18. I've always fitted durgo's 250mm above the cistern level on the highest point of drainage, eg: 1st floor, domestic house bathroom.. anywhere lower risks the traps pulling..
     
  19. Moley

    Moley New Member

    I can't believe this thread. Please tell me you aren't plumbers.

    It's a one way valve, it lets air in not out, this you agree. So what makes you think its going to let water out? You have been told the answer and yet you choose to ignore it. If you don't understand how it works you shouldn't be installing it, alternatively just do as the manufacturer says. Listen to what DIA and M3 have told you.
     
  20. always_learning

    always_learning New Member

    ... :) this is what I don't understand, (amongst many other things...), the height of the AAV above a cistern level does not effect the traps, or the risk of them pulling, THAT is to do with air pressure/depressions within the stack and associated pipe work;
    Think, you could have a stack 100' high, air is the same pressure throughout the pipe, and any branches off that pipe..... so the the AAV height doesn't SEEM to matter?

    Anyway, i think i will put this one down to experience, thanks for all your inputs. :)
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice