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 Daniel Fortunov's Blog » A Plumbing Puzzle

 3 Comments- Add comment | Back to Personal Blog Written on 05-Apr-2010 by asqui

Mixer tap Here’s a puzzle based on the true story of a slight plumbing problem we had when we first moved in to our current home.

Consider the following observations regarding the behaviour of the mixer tap in the bathroom basin:

  • The cold water flow rate is fairly paltry.
  • The hot water flow rate is more reasonable.
  • After washing hands with warm water, turning the mixer to maximum cold yields warm water for a time.
  • When trying to investigate this phenomenon, feeling the water pipes under the basin shows they are both warm.

From this information it should be possible to conclude where the problem lies. However, it is probably not immediately obvious what is going on. (It certainly wasn’t to me, at the time!)

Can you work out where the problem lies?

Click here for a hint.

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  • written on 06-Apr-2010

    DIY says:

    Cold watter pressure lower than that for hot water? (reasons for that may vary) Higher pressure hot water pushes back (via the mixer) and fills the cold water pipe. "Equal pressure" and "no return" valves in various placess throughout the system should prevent this from happening, but they may be faulty, clogged/worn, or missing.

  • written on 09-Apr-2010

    asqui says:

    DIY: Close. The crux of this, which really had me scratching my head, is:
    Even if there is a pressure differential, why would the hot water push back into the cold pipe rather than coming out of the faucet? Surely it's easier to come out from the faucet than to push back against the cold water?

  • written on 16-Apr-2010

    "Uncle" Dave says:

    I only have experience with modern American plumbing and am facinated by the ingenuity of the ancients. I think the mixer is fundamentally a 3-way valve with variable orifices. In other words, the holes are not round, but oblong(?). Moving the mixing "ball" varies the hot/cold openings to create different temperatures. My guess is the mixing ball is in backwards, or made out of alignment, so the discharge, which should come out the faucet, is actually going into the cold side. I'm just guessing at this, but it seems logical to me.

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