Pinholes in CU piping

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by big2bird, Sep 30, 2012.

  1. big2bird

    big2bird IBEW Electrician

    Messages:
    141
    Location:
    Anaheim, Ca.
    I had my home re-plumbed about 1988 in copper tubing. Type L was used. It has a circ. pump with expansion tank, check valves, and the WH is outside in a shack. Now that I am remodeling, and re-piping again, I am just curious. I had perhaps 20 pin holes develop and leak, mainly at fittings, from then until now. Anyone else have this/know the causation?
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,631
    Location:
    Cave Creek, Arizona
    The pump was oversized and not throttled down to maintain a "safe" velocity in the piping. The excessive flow created turbulence at the fittings and eroded the tubing adjacent to them causing the leaks. It is a common problem when someone thinks that a "larger" pump will give better circulation.
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,005
    Location:
    New England
    About the max velocity you want in a pipe is around 5-6 feet/sec, and a recirculations sytem doesn't need to be anywhere near that max.
  4. big2bird

    big2bird IBEW Electrician

    Messages:
    141
    Location:
    Anaheim, Ca.
    Interesting. It is the smallest pump I could find. How can I throttle the flow rate down without affecting flow when needed?

    It is a TACO 1/35 HP. Loop is probably around 120' of 3/4" cu on a horizontal plane, excepting the 5' of head for the WH.
    Last edited: Sep 30, 2012
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,631
    Location:
    Cave Creek, Arizona
    You place a valve in the OUTLET pipe from the pump, NOT the inlet", and close it down until it just maintains the temperature in the pipe. 3/4" is much larger than a recirculation line has to be.
  6. big2bird

    big2bird IBEW Electrician

    Messages:
    141
    Location:
    Anaheim, Ca.
    Okay, I installed a gate valve and throttled it down by half. I'll check later to see if it is too/not enough. Thank you.
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,631
    Location:
    Cave Creek, Arizona
    DId you put the valve on the outlet? IF not and you throttle the flow down you will destroy the pump. THere just has to be enough flow to maintain some temperature in the return line.
  8. big2bird

    big2bird IBEW Electrician

    Messages:
    141
    Location:
    Anaheim, Ca.
    Yes. That is where you said to install it.
  9. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,631
    Location:
    Cave Creek, Arizona
    I just wanted to be sure you read it properly. Sometimes all people see is "put in a valve" and then decide to put it in the easiest way, regardless of where they were told to put it, thinking it didn't make any difference, since a "valve is a valve".
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