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Thread: screwy sound

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  1. #1
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    Talking screwy sound

    hey guys., i am working with a screw machine and when the compressor shuts off for 1 second or so it sounds like it is running backwards., i am thinking that there is still pressure somewhere pushing on the rotors forcing them to turn for about 3 seconds., i know this is what the screw compressors does, just not sure what causes it.,

    thanks fello thermal die nam mik engineers.,
    no signature blast'em man blast'em
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  2. #2
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    As you said, what you are hearing is probably gas flow noise, it takes a second or two for the disharge check valve to close and stop that gas flow.

  3. #3
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    What kind of screw?

  4. #4
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    It's may well be spinning backwards on shutdown. I have a YS thats close to 20 years old and when it shuts down it backspins almost as fast it runs forward. The tech that did the original startup is still in the area and I'm told he cussed the factory the day he started it.

    But its still running everyday!!!
    I'm good at making things cold...You can ask my first two wives!

  5. #5
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    Who's chiller is it anyway

    mlkwal1, What brand is it, If it's a Trane you might just have check valve issues as when the motor stops pumping that check valve should slam shut, right now.-GEO
    Once in a while everything falls into place and I am able to move forward, most of the time it just falls all over the place and I can't go anywhere-GEO

  6. #6
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    sorry guys ., it is a rtaa 140
    no signature blast'em man blast'em
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  7. #7
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    As I said

    Change out the check valves-now. -GEO
    Once in a while everything falls into place and I am able to move forward, most of the time it just falls all over the place and I can't go anywhere-GEO

  8. #8
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    Depending on the volumn of the seperators and the pressure differentials............ yep, you can get a back peddle, even with functioning checks.
    \m/
    original member of the racoon brotherhood

  9. #9
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    The groan followed by the slapping sound on an RTAA is normal and yes it will be more obvious if the differentials are higher , dont be rushing to change the check valves coz it wont sound any different with new ones .
    The 64 roars to life Whoo hoo ...shes a rolling chassis .
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  10. #10
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    Quote Originally Posted by graham View Post
    The groan followed by the slapping sound on an RTAA is normal and yes it will be more obvious if the differentials are higher , dont be rushing to change the check valves coz it wont sound any different with new ones .
    Agreed!

  11. #11
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    Not quite Guys

    If the rotors on a GP compressor are allowed to backspin they will put an opposing thrusting force and eventually cause rotors to make contact. I don't think Trane change their guidelines from the mid-nineties. The development engineer for the smaller RTAA's 70-125 ton said there should no back-spinning of the rotors on shutdown. It could go bang, pop slap itself around a few times but never turn in reverse. There was a notice to this problem passed out during the early Pueblo classes, (memo not a service bulletin) -GEO
    Once in a while everything falls into place and I am able to move forward, most of the time it just falls all over the place and I can't go anywhere-GEO

  12. #12
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    Quote Originally Posted by ga1279 View Post
    If the rotors on a GP compressor are allowed to backspin they will put an opposing thrusting force and eventually cause rotors to make contact. I don't think Trane change their guidelines from the mid-nineties. The development engineer for the smaller RTAA's 70-125 ton said there should no back-spinning of the rotors on shutdown. It could go bang, pop slap itself around a few times but never turn in reverse. There was a notice to this problem passed out during the early Pueblo classes, (memo not a service bulletin) -GEO
    First of all, the RTAA140 doesn't have GP compressors, it has intermediate compressors.

    It doesn't hurt the compressor to backspin for a short amount of time on shutdown as a result of pressures equalizing. The thrust is still against the thrust bearing when the presssures are equalizing. As a matter of fact, the RTHC and RTHD compressors don't have a 100% sealing check valve and they will roar for several seconds on shutdown. It is bad however, for a screw compressor to be powered running backwards as there is no thrust bearing on the opposite side of the rotors.

  13. #13
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    Nope has chunk compressors .. check valve is most definitely bad. When I shut down circle 1 . Back spins for about 5 seconds. Sounds like a jet engine. And I don't hear the slap. When I shut down circle 2 .I hear the slap and the compressor shuts off..
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