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  1. #1
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    Choking Suction Port



    Just wondering, if system is over capacity and to reduce the same, if we close the rota-lockvalve (King valve) on the suction side.

    This will reduce the pressure in the compressor, reducing the compression ration but will increase the evaporator pressure.

    Any drawback, like compressor motor cooling, oil returns, etc.



  2. #2
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    Re: Choking Suction Port

    Hi jwasir

    to maintain evap pressure use a EPR and for compressor use a CPR

    this link will help https://docs.google.com/viewer?a=v&p...lNmUw&hl=en_GB

    more docs here http://www.refrigeration-engineer.co...Tips&highlight=

    and here http://www.refrigeration-engineer.co...tins&highlight=

    R's chillerman
    If the World did not Suck, We would all fall off !

  3. #3
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    Re: Choking Suction Port

    Sure!! Just a thought, how is choking different than using EPR & CPR??

  4. #4
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    Re: Choking Suction Port

    Quote Originally Posted by jwasir View Post
    Sure!! Just a thought, how is choking different than using EPR & CPR??
    with an epr/cpr you control a pressure which remains constant, by closing off the suction port you restrict the flow, which is then variable depending on the fluctuating suction pressure


    R's chillerman
    Last edited by chillerman2006; 15-10-2011 at 05:32 PM.
    If the World did not Suck, We would all fall off !

  5. #5
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    Re: Choking Suction Port

    Quote Originally Posted by jwasir View Post
    Just wondering, if system is over capacity and to reduce the same, if we close the rota-lockvalve (King valve) on the suction side.
    This will reduce the pressure in the compressor, reducing the compression ration but will increase the evaporator pressure.
    Any drawback, like compressor motor cooling, oil returns, etc.
    One drawback not mentioned here.
    If you partially close the suction valve you INCREASE the compression ratio. This can put the compressor out of it recommended parameters. Discharge temperatures will increase. This can case shortened discharge valve life at the very least.

  6. #6
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    Re: Choking Suction Port

    Quote Originally Posted by NH3LVR View Post
    One drawback not mentioned here.
    If you partially close the suction valve you INCREASE the compression ratio. This can put the compressor out of it recommended parameters. Discharge temperatures will increase. This can case shortened discharge valve life at the very least.
    Sir,

    I practically checked this, CR almost stays constant. Is CPR not doing the same thing as what we do by closing the port!

  7. #7
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    Re: Choking Suction Port

    Quote Originally Posted by jwasir View Post
    Is CPR not doing the same thing as what we do by closing the port!
    with an epr/cpr you control a pressure which remains constant, by closing off the suction port you restrict the flow, which is then variable depending on the fluctuating suction pressure
    If the World did not Suck, We would all fall off !

  8. #8
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    Re: Choking Suction Port

    Quote Originally Posted by jwasir View Post
    Sir,

    I practically checked this, CR almost stays constant. Is CPR not doing the same thing as what we do by closing the port!
    Just to make sure that we are talking the about the same thing here I will give an example. Sorry about the Imperial units, it is all we know in the USA.
    Compression ratio is calculated by dividing the discharge pressure absolute by the suction pressure absolute.
    Example: suction pressure 10lbs gauge-discharge 150lbs gauge. Add 14.7 pounds to each for 24.7lbs and 164.7. Divide and you get a compression ratio of 6.67.
    Remember I am an industrial refrigeration person with limited commercial experience. I have seen ammonia compressors ruined by running too high a compression ratio. Unless your discharge pressure falls when you restrict the suction your compression ratio goes up. If the discharge temperature goes too high you will have problems.
    A CPR is useful to eliminate motor overload on start-up and after defrost. A EPR is useful to maintain a more appropriate suction pressure in a room for example. However they cause a lack of efficiency because the gas is being compressed at a less dense state. Remember that the total refrigerant effect is dependent on the amount of refrigerant being circulated through the system. Lower suction pressure=less refrigerant being circulated=lower capacity. Higher discharge=a less efficient compressor=reduced capacity.

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