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  1. #1
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    Slide Valve Operation


    Hi - I'm new to this board but I want to know how the 'internals' of the compressor slide work. I understand the general overview.. in that by using the capacity slide valve the effect length of the rotor is reduced and thus less refrigerant can be compressed reducing the overall flow rate.

    Where I get stuck is understanding how the Vi changes, or if at all, when a compressor begins to unload.

    Refer to this picture.. of a Variable Vi MYCOM Compressor. Would the Vi not change as the slide valve moves to the right (unloads). Basically, would Vi = L not essentially become Vi = M as it begins to unload? I thought the slide stop just dictated the Vi at full load.. but i've had conflicting reports with MYCOM technical support.Untitled.jpg

    Any help would be greatly appreciated as not knowing is driving me mad.



  2. #2
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    Re: Slide Valve Operation

    In further reading, I've come across that the slide stop basically dictates the Volume of gas coming in. Is this the case? (Refrigerant comes in to the left of the grey box above).. Therefore the Vi must be constant as when the slide valve moves to the right (volume of gas goes down) but the volume at discharge as goes down (pressure does up) maintaing the Vi.

    If so.. wouldn't this indicate that the internal discharge pressure would increase as your Vi setting goes up. This seems like wasted energy to me.. and that an auto Vi which can match the compressor's discharge pressure to the system's discharge pressure would be much more efficient

  3. #3
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    Re: Slide Valve Operation

    VI relates to compression ratios, variable discharge port size, either as a booster on compounded systems or single stage compression. Mycom have 3 options L M & H, the setting is done manually depending on application.
    L set on a booster ensures high vapour transfer at low ratios , M & H for single stage compression ratios for medium temp and low temp SST.

  4. #4
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    Re: Slide Valve Operation

    Quote Originally Posted by justinrmac View Post
    In further reading, I've come across that the slide stop basically dictates the Volume of gas coming in. Is this the case? (Refrigerant comes in to the left of the grey box above).. Therefore the Vi must be constant as when the slide valve moves to the right (volume of gas goes down) but the volume at discharge as goes down (pressure does up) maintaing the Vi.

    If so.. wouldn't this indicate that the internal discharge pressure would increase as your Vi setting goes up. This seems like wasted energy to me.. and that an auto Vi which can match the compressor's discharge pressure to the system's discharge pressure would be much more efficient
    The slide stop effects total travel of slide valve which in turn alters compression ratio at full load.
    It does not dictate volume of gas coming into compressor, the slide valve does that.
    As Magoo states Mycom have L,M,H ratio's for different duties or differential between suction & discharge pressures.
    If incorrect ratio is set the Vi ratio can effect efficiency over or under compression of gas.
    This will effect capacity & power used to do the job.
    Mycom do have a auto Vi as well as Frick,Grasso etc.
    The Vi port works best as does the screw compressor at 100% full load.
    Mycom you can change Vi setting seasonally (in "V" series) if you want most efficient operation, but not many people would bother.

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