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Discuss Why would it be wrong to run a shower pump on 15mm? in the Bathrooms, Showers and Wetrooms area at UKPlumbersForums.co.uk.

  1. Ric2013

    Ric2013 Plumber

    Apart from the obvious answer which is this would not be to manufacturer's instructions and would void any warranty.

    I was having a discussion the other day with a builder who wanted to run the cold side of a 1.5Bar twin-impeller pump from a dedicated cold distributing pipe in 15mm. He claims this is what he has always done in the past and it works (I would imagine this is true, to some degree).

    I have looked at the MI, which state that the suction side of the pump should be 22mm and reduce to 15 close to the 15mm tails supplied with the pump. Common logic would be that 22 is required because the suction side is gravity, but, while I know 15mm would be wrong, I'm trying to understand WHY it would be wrong.

    My feeling is that, since 15mm on the delivery side of the pump is considered sufficient, and that the flow rate will be the same on both suction and delivery sides, 15mm is enough for flow on suction side. However, I would imagine the risk is cavitation, leading to premature failure of the pump impeller and possible the pipework or fittings on the suction side of the pump.

    Do people feel my understanding is correct?

    Thank you,


    R
     
  2. rpm

    rpm Trusted Plumber

    Many pumps insist on a larger inlet and a smaller outlet, cavitation is basically trapped air becoming very hot and popping / exploding.
     
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  3. king of pipes

    king of pipes Trusted Plumber GSR

    I have done plenty in 15mm not any dramas.
     
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  4. Harvest Fields

    Harvest Fields Trusted Plumber GSR Top Contributor!!

    Never done one myself in 15mm always have the feeds in 22mm, but I have replaced loads of existing ones that have both feeds in 15mm and they have been running for years. But best practice is definitely 22mm. I always recommend the pipes are upgraded
     
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  5. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    I've done it but only if there a short run to the pump
     
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  6. Harvest Fields

    Harvest Fields Trusted Plumber GSR Top Contributor!!

    Maybe if the CWS was straight above the cylinder. But I would still have a bad nights sleep:p:p:p
     
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  7. townfanjon

    townfanjon Trusted Plumber GSR

    I thought that was because you followed Villa lol
     
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  8. king of pipes

    king of pipes Trusted Plumber GSR

    Sleep like a baby ha ha , mind you i didnt last night have had a git of a job this week a boiler swap cylinder change and controls upgrade , electrian wired something wrong and i had air and circulation issues but got it sorted today so happy days , sacked work off tomorrow having a slack day paperwork and catching up with people
     
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    • Optimistic Optimistic x 1
  9. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    :D until someone phones in saying ive got water everywhere
     
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  10. mache

    mache Active Member

    not quite correct description. Cavitation occurs when pump impeller or sharp edge even causes a low pressure area in which a vacuum pocket forms. When that pocket collapses the violet energy change can rip material off the surface of any material it is in contact with. But I do agree that a restricted protracted inlet (e.g. full length of 15mm run) could increase the chance of cavitation occurring.
     
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  11. king of pipes

    king of pipes Trusted Plumber GSR

    Not tomorrow shauny had enough this week bud, mind you got a fancy rad to fit saturday so my weeks not over yet whats your week been like ?


    Nice one mache learn something new every day
     
  12. Harvest Fields

    Harvest Fields Trusted Plumber GSR Top Contributor!!

    Cheeky;)think we will do ok this season. Ow though. Still sacked my season ticket off though.
     
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  13. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    busy

    finished off a cloak room sink / vanity 2 cabinets new cc toilet shower head replacement

    now starting a full down stairs bathroom
     
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  14. Harvest Fields

    Harvest Fields Trusted Plumber GSR Top Contributor!!

    At least you don't have to cart the bath upstairs:)
     
  15. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    no bath and already done the upsairs one :D
     
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