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Kinks in soft copper

But also weakens it...alas my son, I have kinked many a line set in my day...Dad made my brother and I pay for it out of our paychecks, you learn faster that way! Before pre-insulated lines came to the market, we would have to slide the Armaflex on the suction line...first time I did it, I did NOT cover the open end of the pipe, consequently skinning shards of insulation INTO the pipe! This really caused some serious issues upon startup! Dad made me pay for that one too!...God Bless all of the DEAD MEN!


  • PeterGriffin
    PeterGriffin Member Posts: 79

    I'm a plumbing apprentice and I'm starting to install the linesets for air conditioning. I've been told not to kink the copper and that's fine, but I haven't got a good explanation why. The best I can come up with on my own is that the kink would create friction causing the temperature to slightly rise ? Any good?


  • jim lockard
    jim lockard Member Posts: 1,059

    Next time you are washing your car or watering the garden put a kink in the hose. The same thing that happens with your garden hose is what happens when you kink a refrigerant line.
    Hopefully your employer is taking the time to teach you the proper way to handle refrigerant copper. Best Wishes J.Lockard
  • Brad White_9
    Brad White_9 Member Posts: 2,440
    Take a piece of scrap copper tubing...

    Scrap??? OK, take a breath. This is science...

    Bend it, kink it anyway you want to. Cut the joint lengthwise at the kink and see what happens to the structure. Mikey is right. Weakens the tubing at the structural level and it cannot be made right. Copper is "work hardened" so bending it makes it harder yet more brittle. Cracks develop, ones that you cannot see. Best practice is to replace. Second best is to braze in a straight section. The lick and a promise method is to heat it with a torch and let it cool to soften it. Don't bother. You will never know if it will leak; if anywhere it will leak at the kink.
  • Empire_2
    Empire_2 Member Posts: 2,343
    yellow jacket tubing Bender:

    Love this product and it goes up to 7/8" tubing.

    Mike T.
  • dana_3
    dana_3 Member Posts: 57

    just the opposite. kinks can cause lo suction pressure. frosting of the suction line. evaporator, and compressor. eventually leading to premature compressor failure
  • bob_50
    bob_50 Member Posts: 306

    Think about aspect ratio. If you build a house and you are limited to 200 feet of wall. If you build a round house it will have approx 3215 square feet of floor area. If you build it square, 50X50 it will have 2500 square feet. If you build it rectangular 10X90 it will have 900 square feet. The same thing applies to pipe of ANY kind or duct. With copper refrigeration lines the problem is usually with the suction line. As the line flatens due to bending it's crossectional area is decreasing. This cause more pressure drop which increases the compression ratio which reduces the volumetric efficiency of the compressor. System capacity is reduced.
  • PeterGriffin
    PeterGriffin Member Posts: 79
    thank you

    Thank you all so much for the excellent replies. The response I got of my boss is along the lines of "It just restricts the flow." I'm very eager to learn all of these things, anything more that I learn makes me that much more knowledgeable, but really, the only "training" I got out of this was:
    1: Don't kink the copper
    2: This is how you weld
    3: Crack the valve and listen for leaks, use leak detector if you have any.
    4: Collect

    I don't want to trash my boss, but there's alot of things I'm sure we are supposed to do that we aren't doing when we are installing furnaces and A/C.
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    All correct

    All of the responses provided to you thus far have been correct. Please add this to the mix.

    Consider a simple electric circuit. As the resistance of the circuit increases, the amount of current flow will decrease. Lowering the current flow will reduce the amount of "work" as related to the power consumed by the circuit. The electrical power consumed by a circuit (assuming a power factor of 1) is determined by multiplying the supply voltage by the current flow. The lower the current flow, the lower the power.

    Sorry for going off on a tangent... Ahem...

    Back to your question...

    By kinking a section of copper tubing, you are reducing the cross sectional area of the tubing. By doing this, a restriction has been created in the piping circuit. By increasing the resistance to flow, there will be less refrigerant flow through the system. More refrigerant will be trapped on the high side, possibly causing the head pressure to rise, and there will be a deficiency of refrigerant on the low side, possibly causing the low side pressure to drop. (The "possibly" part comes from the fact that the kink may not be very large as well as the fact that AXVs and TXVs may be able to compensate for this restriction if it is small enough).

    For example, a TXV gets paid to maintain constant evaporator superheat. If there is a kink in the liquid line, for example, there will be less refrigerant feeding through the TXV and into the evaporator. This will cause (temporarily) the evapoerator superheat to rise. This will cause the TXV to open, bringing the superheat back to its setpoint. However, if the kink is severe, the TXV may not be able to maintain the desired superheat even if the vale opens all the way.

    One other thought...

    By kinking a refrigerant line, as mentioned before, yo are adding resistance to, and decreasing, the refrigerant flow. This will lower the mass flow rate of the system and lead to reduced evaporator capacity.

    The bottom line is... Don't kink your refrigerant lines!

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