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Thread: Threading a Poly pipe tee

  1. #1
    Supporting Member Frank S's Avatar
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    Threading a Poly pipe tee

    Some of the plumbing in my pump house has 1: pex tubing stretched over poly tees made for thinner poly pipe I was needing to install a frost free hose bib to the outside f the pump house so the pex pipe either had to be shortened or replaced.
    the gray threaded Schedule 80 PVC pipes can survive frozen conditions without bursting but how to transition from one type of fitting to another without having to add a barbed nipple to the end of the Pex tube on the Tee
    My solution was to use a pipe threading die. But the problem there is most pipe dies have a guide the pipe passes through toe keep the threading operation square to the pipe.
    I grabbed my Rigid 3/4" die and thought about removing the independent cutters and turning them over but then I remembered my antique REED pipe die set the dies are mono block just like bold dies It was a simple manor to remove the holding screws and flip the die in the housing then thread the Tee
    Threading a Poly pipe tee-img_20210723_162817.jpg
    Then just saw off the start taper of the barbed nipple
    Threading a Poly pipe tee-img_20210723_163350.jpg
    Threading a Poly pipe tee-img_20210723_163451.jpg
    Threading a Poly pipe tee-img_20210723_163903f.jpg

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    Supporting Member hemmjo's Avatar
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    Frank wrote;"..the gray threaded Schedule 80 PVC pipes can survive frozen conditions without bursting.."

    Have to be careful with a blanket statement here. There are conditions here all pipes can "survive" freezing conditions, but also conditions that can burst all types of pipes.

    The physics of pipes bursting it miss understood by may, even in the trades.

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    Supporting Member Frank S's Avatar
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    Quote Originally Posted by hemmjo View Post
    Frank wrote;"..the gray threaded Schedule 80 PVC pipes can survive frozen conditions without bursting.."

    Have to be careful with a blanket statement here. There are conditions here all pipes can "survive" freezing conditions, but also conditions that can burst all types of pipes.

    The physics of pipes bursting it miss understood by may, even in the trades.
    yes actually I should have included the conditions of my area were it hardly ever gets below zero f
    Water expands rapidly as it freezes down to a certain temperature then slows but for the most part will keep expanding until it reaches the point where the molecules have slowed to the point of little movement I believe it would reach almost absolute zero before they completely stop any movement and the expansion would also stop. but after around -20f ambient the expansion rate is so miniscule it would not be much of a factor in a pipe it is the ability of what ever containment the water is to retain its burst strength at lower temperatures is the key factor. regular white PVC seems to be the first to lose out followed by thin copper pipes especially older ones. Thicker new copper loses at the sweat connections Thin poly pipe will keep expanding until it forces its connections to fail thicker PEX is the same way. the gray PVC or CPVC in sch 80 will retain its strength much longer due to the thickness and the ability to resist becoming brittle much longer and largely depends on the connections at that point as well glued may actually have an advantage over threaded in some cases if the bonding agent caused a near perfect weld that will not deteriorate when cold. heat fused urethane piping seems to be a much more durable choice but if the internal pressures reach the critical limit even that will fail.
    I've seen several inch thick steel assemblies succumb to even comparatively small volumes of water providing it got cold enough.
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    Supporting Member hemmjo's Avatar
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    Actually at standard pressures fresh water is the most dense at 4˚ C. It becomes ice and expands about 9% at 0˚C . As the temperature drops below 0˚C the ice actually becomes more dense again (shrinks), but never reaches the density of liquid water. Thus, ice always floats.

    The physics of bursting has more to do with how the water freezes in relation to the total piping system. Where the source of the cold and the ice formation occurs in relation to the rest of the piping system. The ice itself does not burst the pipes. Ice itself is very ductile, if can move and deform under steady pressure without breaking. It is the expanding water that bursts pipes. As the water in a pipe begins to freeze the ice takes the shape and size of the pipe. As the ice is formed the expanding water causes pressure to build in the pipe, just it would do if you were heating the water. If the water has a place to go, such as back into the house to a warmer place, the pipe will not break. The ice will continue to form along the inside of the pipe, pushing the liquid water out of the way.

    If the water is trapped and cannot escape to someplace in the system, the pressure in the pipe will build until the pipe bursts at the weakest spot available. The same as if you heat water in a closed system.

    Try it.... get two pipes the same size about 16" (40.6cm)long. Copper is the more dramatic but expensive. Put a cap on one end and fit the other end with a fitting you can thread a gauge into. Fill both pipes completely with fresh water. Fit the gauge on one pipe, fit a plug into the other pipe so it is totally sealed and there is NO AIR in the pipe.

    Then either drill two holes in the top of your wife's freezer (not recommended), OR a better idea, fill a 5 gallon bucket with ice and add salt like you would making ice-cream. Insert the pipes fully into the ice bath with the gauge and the plugged end out of the water. Watch as the gauge builds pressure. When the gauge nears the burst pressure of your test pipe... stand back. If you let this experiment continue to completion, you will find the break at the top where the liquid water is. The ice began to form at the bottom of the pipe, pushing the water upward until the pipe burst. The pipe where the ice formed will be undamaged.

    There is also a miss conception that the pipes burst when the ice melts. This myth is caused by the fact that if a system freezes, the ice plug often isolates the damaged section from the break. The ice forms, seals the pipe to separate one section from the main supply section. Then as the freezing continues, the pressure builds in the isolated section, the pipe bursts, a little water leaks out, but no one notices. Then as the thaw comes along, the plug melts and the flooding begins

    Obviously it does not always happen this way, but I have see this occur many times, and have done many repairs caused by this.

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    Frank S (Jul 30, 2021)

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    Thanks Frank S! We've added your Threaded Poly Pipe Tee to our Miscellaneous category,
    as well as to your builder page: Frank S's Homemade Tools. Your receipt:






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