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  1. #1
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    Copeland Tandem Scroll



    Hi has anyone had issues with these tandem pairs?
    We have seen cases where one compressor was running and the discharge gas was being recirculated through the stationary compressor. The NRV/Check valve on the stationary compressor does not seem man enough to hold the pressure.
    We are considering fitting an extra NRV on each discharge "manifold"
    Would like to know if anyone else has had the same issue.



  2. #2
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    Re: Copeland Tandem Scroll

    Don't come across a lot of tandems but i have fitted external check valves on a good few rack compressors with no problems.

  3. #3
    Brian_UK's Avatar
    Brian_UK is online now Moderator I am starting to push the Mods: of RE Site Moderator : and general nice guy
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    Re: Copeland Tandem Scroll

    What indication are you having to suggest recirculating discharge gas?
    Brian - Newton Abbot, Devon, UK
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  4. #4
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    Re: Copeland Tandem Scroll

    The internal discharge check valves are an inherent weakness in scroll compressors and even more so in variable speed scrolls. It can be difficult to size a discharge check valve due to the mass flow changing as conditions change. An oversize check valve will constantly oscillate from open to close and destroying the check valves seat causing back flow leakage. An undersized check valve will cause high pressure drops and noise issues. Some scrolls simply use a flat plate as the check valve with no spring, some fit a spring loaded check valve which often fails due to system conditions. So the alternative is to fit an external check valve in the discharge line not to close to the compressor . Most engineers simply line size the check valve, but often a size smaller is beneficial to prevent it chattering. Many scroll systems have an external check valve fitted where it’s internal nrv has failed or leaks. When the check valve has failed , when the running compressor shuts down, the discharge gas rapidly blows back through scrolls causing the scrolls to go on reverse , the noise sounds like a Motorbike accerating to 100mph then as the pressure equalises “suction to discharge “ the noise slows down and stops. So a cheap fix is to fit an NRV externally to solve the problem and save on replacing the compressor.

  5. #5
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    Re: Copeland Tandem Scroll

    Quote Originally Posted by Glenn Moore View Post
    The internal discharge check valves are an inherent weakness in scroll compressors and even more so in variable speed scrolls. It can be difficult to size a discharge check valve due to the mass flow changing as conditions change. An oversize check valve will constantly oscillate from open to close and destroying the check valves seat causing back flow leakage. An undersized check valve will cause high pressure drops and noise issues. Some scrolls simply use a flat plate as the check valve with no spring, some fit a spring loaded check valve which often fails due to system conditions. So the alternative is to fit an external check valve in the discharge line not to close to the compressor . Most engineers simply line size the check valve, but often a size smaller is beneficial to prevent it chattering. Many scroll systems have an external check valve fitted where it’s internal nrv has failed or leaks. When the check valve has failed , when the running compressor shuts down, the discharge gas rapidly blows back through scrolls causing the scrolls to go on reverse , the noise sounds like a Motorbike accerating to 100mph then as the pressure equalises “suction to discharge “ the noise slows down and stops. So a cheap fix is to fit an NRV externally to solve the problem and save on replacing the compressor.
    Nice response, would give you rep points, but apparently I've already given you some and have to spread them around more, before I can give back to you!

    Just a point of clarification on original post, I wouldn't add another NRV in the same line as an existing one..if thats what O.P. was saying. Would replace existing with new, better quality and along Glenn Moore's advice.

  6. #6
    Brian_UK's Avatar
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    Re: Copeland Tandem Scroll

    ^^ Tandem scrolls have the NRV built into the discharge stub so tricky to remove, if at all.
    Brian - Newton Abbot, Devon, UK
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