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  1. #1
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    Dec 2008
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    Seattle WA
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    Sanyo Screw Compressors SR-3UL

    I have a set of 4 Sanyo SR-3UL screw compressors in a mammoth unit, each compressor has a 'load' solenoid, and an 'unload' solenoid.
    From the wiring diagram, it looks like on compressor start-up BOTH are energized for 20 seconds, then a time delay relay picks up and releases them to the control system.
    The control system is wired to one control relay that causes all 4 load solenoids to operate, and one control relay causes all 4 unload solenoids to operate.
    My questions:
    1) What exactly do the load/unload solenoids do? Do they push a slide valve back and forth inside the compressor?
    2) What happens when they are BOTH energized? (Which one wins?)
    3) I am assuming a sequence like this:
    On increasing load -
    1) Unload , start compressor 1
    2) Load Compressor 1
    3) Unload, start compressor 2
    4) Load compressors 1&2
    5) Unload, start compressor 3
    6) Load compressors 1,2,3
    7) Unload, start compressor 4
    8) Load compressors 1,2,3,4
    On decreasing load, reverse this.

    Anyone see an issue with this sequence? With one control relay hitting all 4 unloaders, and one hitting all 4 unloaders, I don't see another way to do it. The wiring that causes this is all Mammoth Factory Wiring, and I don't want to cut into that.
    Thanks in advance!
    John

  2. #2
    Join Date
    Jun 2011
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    A lot of screw compressors have a sliding plate that opens and closes a slot along the screws, which increases or decreases capacity. Sounds like this one might have a series of ports controlled by solenoids that do the same thing. Also, sometimes compressors are unloaded for start up to ease the inrush amps (easier on the electric bill AND the compressor).

    I don't know for sure though, it's just my best guess.

  3. #3
    Join Date
    Dec 2012
    Location
    Lowell,MA
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    mammoth uses " pump out" compressor starts unloaded 20 seconds later, llsv opens (supposed to be more energy efficient )haven't seen sanyo's, they mostly use copeland now but sequence sounds right maybe both have to be energized for start unloaded, those solenoid valves open oil ports internal to compressor, maybe you could find diagram of oil passages on those sanyo's to better understand the way it loads and unloads

  4. #4
    Join Date
    Feb 2009
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    Miami, Florida
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    Usually they will operate in this order:
    Compressor loading: Load solenoid valve opens and unload solenoid closes, pressurized oil flow enter the cylinder and with the help of the suction acting on the face of the slide valve forces the piston towards the rotor. End result more compression, this is basically done as the heat load is increasing.
    Compressor Unloading: Load solenoid valve closes and unload solenoid valve opens, now the oil trapped within the cylinder is drawn out into the lower pressure suction area of the compressor, as the pressurized oil leaves the cylinder the slide valve gradually moves away from the rotors, now there’s less available are to compress, controller start to unload as you get closer to your setpoint.
    Now if both solenoid valve close then the present level of compressor load is maintain, you will have a constant oil pressure applied to the face of the slide valve.

  5. #5
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    Dec 2008
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    Seattle WA
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    Thread Starter
    Update: My mistake, they are FU Sheng compressors...
    Also, the unload and load relays are two separate relays. Do I start a compressor with "unload" energized, then de energize for more capacity, then energize "load" for still more capacity? (Do these compressors have 3 levels of capacity? If so, what % is each level?)

    No manuals on this unit...Help?

  6. #6
    Join Date
    Dec 2012
    Location
    Lowell,MA
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    it is infinite load unload they don't step them you could be anywhere from 25% to 100%

  7. #7
    Join Date
    Feb 2009
    Location
    Miami, Florida
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    John
    You shouldn’t be controlling compressor capacity at all; these are expensive piece of equipments which usually come with an integral control that has been programmed to perform its operation including safeties, sequence of operation and control algorithm.
    Usually they will provide a set of open contacts for remote start/stop, fire alarm, Remote emergency stop, supply or return temperature reset, etc. But as a general rule you shouldn’t be involve in compressor capacity control due to its extreme complexity, not saying that is not possible; but manufacturer will most of the time, if not all, provide their own microprocessor based controller.
    Check your e-mail.

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