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  1. #1
    Join Date
    May 2005
    Location
    kansas
    Posts
    5

    Hmm

    I am going to school for HVAC, and after one of our tests we found that just about every one was corn fused about clearance volume to compression ratio in a reciporcating compressor. The question was: If the compression ratio changes in a reciporcating compressor does the clearance volume change? And why? I just maby just use to working on diesel engines, but to me if the compression ratio changes then something has to change also, and if I am on the right track then the clearance volume should change to?

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,289
    If I'm not mistaken, clearance volume in a reciprocating compressor is the distance between the piston head when the piston is at top dead center and the bottom of the cylinder head. This clearance should be the same each time the piston is at TDC.

    Compression ratio is a relationship between suction and discharge pressures. The greater of a spread that exists between these two pressures, the higher the compression ratio.

    When the discharge valve on a recip compressor closes and the piston begins descending, the suction valve will open once the pressure in the cylinder drops below the vapor pressure in the suction line. A compressor with a greater clearance volume will also have to overcome this volume plus the volume necessary to drop cylinder pressure below suction vapor pressure in order to draw in suction gas to be compressed into high pressure vapor.

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  3. #3
    Join Date
    Dec 2002
    Location
    davenport, iowa
    Posts
    778
    not always so; rarification of refrigerant vapors will change compression ratio and doesn't involve the changing of clearance volume read something to that effect once.
    Da Threadkilla

  4. #4
    Join Date
    Apr 2005
    Location
    Southern Ca
    Posts
    67
    Originally posted by overnightflight
    I am going to school for HVAC, and after one of our tests we found that just about every one was corn fused about clearance volume to compression ratio in a reciporcating compressor. The question was: If the compression ratio changes in a reciporcating compressor does the clearance volume change? And why? I just maby just use to working on diesel engines, but to me if the compression ratio changes then something has to change also, and if I am on the right track then the clearance volume should change to?
    Corn fused? I hope you meant confused


    When the suction pressure and/or discharge pressure changes, so does the compression ratio. Diesel engines don't have to worry as much about intake pressure or exhaust pressure since its only restrictions are in intake filters and mufflers. With a completely sealed refrigeration cycle, the entire refrigeration system is affected by its other parts (condenser, metering device, evap, ect). The amount of refrigerant is always the same, so the more you have in place X, the less you'll have at place Y, so pressures in one place affect the other.


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