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Thread: Pinholes in CU piping

  1. #1
    IBEW Electrician big2bird's Avatar
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    Question Pinholes in CU piping

    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?

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    Moderator & Master Plumber hj's Avatar
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    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.
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    Retired Defense Industry Engineer jadnashua's Avatar
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    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.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    IBEW Electrician big2bird's Avatar
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    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 by big2bird; 09-30-2012 at 07:46 PM.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    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.
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    IBEW Electrician big2bird's Avatar
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    Quote Originally Posted by hj View Post
    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.
    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.

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    Moderator & Master Plumber hj's Avatar
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    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.
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    IBEW Electrician big2bird's Avatar
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    Quote Originally Posted by hj View Post
    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.
    Yes. That is where you said to install it.

  9. #9
    Moderator & Master Plumber hj's Avatar
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    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".
    Licensed residential and commercial plumber

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