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Mixer Basin Tap?

Discussion in 'Plumbing and Central Heating' started by jcp, 4 Nov 2019.

  1. jcp

    jcp

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    Hi

    I need to replace a bathroom basin and 2-taps, and the family want a 'modern' mixer-tap. The old plumbing has mains cold water and loft pressure hot water. Is there a suitable pressure reducing valve I could put on the cold, or do I need to provide a loft pressure cold supply? And, isn't the mains pressure cold to provide drinking water quality at the basin?

    Any advice welcome.
     
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  3. johnny2007

    johnny2007

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    Simply fit full bore isolating valves and if needed close the cold by as much as you want so to reduce the pressure.
    Mind you, mixer taps come in 2 forms, suitable for high pressure only and suitable for low pressure.
    You need a low pressure.
     
  4. The Novice

    The Novice

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    Closing down will only reduce flow, not pressure. You will need to fit a check valve if fitting onto unbalanced supplies, failing that take a feed from loft.
     
  5. johnny2007

    johnny2007

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    Yes, reducing cold flow will balance the tap.
     
  6. The Novice

    The Novice

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    Yes with a pressure reducing valve, not an isolating valve.
     
  7. johnny2007

    johnny2007

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    It works with isolating valve.
    Done hundreds of times.
     
  8. Madrab

    Madrab

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    It's pressure that can be the issue not flow when mixing mains with gravity, in a mix in the body monobloc, turning the ISO valve can sometimes work but it just drops the flow not pressure. It really depends on how big the difference between each is, whether using the ISO works or not, that and they tend to get noisy when using them to restrict the flow.

    The ideal is to use a dual flow basin mixer/mono tap, then the water doesn't mix in the body where balanced pressure is important, it mixes at the end of the spout. Not a huge selection to choose from though.
     
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  10. JimCrow

    JimCrow

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  11. jcp

    jcp

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    Thanks all for your comments, but I was specifically asking about a pressure reducing valve, not half closing an isolating valve.

    I have used a half closed Iso-valve to roughly balance flow to a bridge tap (separate internal pipes until end of spout) in the kitchen. This too has mains pressure cold supply and loft pressure hot. However, each feed of a bridge tap has its own this tap valve, so flow rates can be adjusted independently to get a balance. I'm not sure this is true of a "monoblock" type tap - would I have to adjust the single lever side to side when I move it up and down to adjust the combined flow?
     
  12. JohnD

    JohnD

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    https://www.caleffi.com/international/en-int/pressure-reducing-valves

    I've got one

    [​IMG]

    About £30

    there's another version where the hot pipe and the cold pipe pass through the body of the valve, both apply pressure to a diaphagm. If pressure is unequal a needle or something moves to restrict the higher pressure side.

    Very useful for showers I believe
     
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  13. Madrab

    Madrab

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    it's called a dual flow tap, a bridge tap is something different.

    yes, to do it more accurately, you need either a pressure reducing valve

    or a pressure equalising valve.

    The trouble with those is that the pressure of both will have to be dropped to the lower value so the flow out the tap may be reduced by a fair amount.
     
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  14. oldbuffer

    oldbuffer

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    As Madrab has said, a pressure equalizing valve will reduce the pressure of both hot and cold to (at best) the lower of the two, in your case almost certainly the hot. If the basin is on the floor below the loft cold water storage cistern, the difference in height between the base of the CWSC and the tap determines the available pressure head. If this is the case you'd be lucky to get 0.2 bar of pressure, and many modern mixer taps just won't work on such a low pressure. Make sure you know the minimum pressure rating of any tap that you propose buying, preferably with its flow rate in litres per minute at that minimum pressure.
     
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  15. JohnD

    JohnD

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    Tell them they can't have one.
     
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