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  1. #1
    Join Date
    Aug 2003
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    30

    Hmm

    can't seem to understand rack systems! need a sight or reading material for more of a understanding please.

  2. #2
    Join Date
    Oct 2001
    Location
    Stoney Creek, Ontario
    Posts
    884
    no sight , no reading, just experience


  3. #3
    Join Date
    May 2004
    Location
    Ponchatoula, LA
    Posts
    84
    What exactly do you want to know? I think of them as a multi stage compressor. Each individual compressor is a stage of the larger whole (the rack). Specific companies have little idiosyncrasies but the basic premise is to maintain a specific suction pressure group, by turning on and off compressors. Since each compressor is unique and needs it's own oil and has different crankcase pressures based on it being on or off, there has to be some type of oiling system to ensure every compressor has the proper amount. Tyler uses a balanced approach with an equalization line so that no compressor over fills. Hussman uses and expansion valve style with solenoids to prevent pump outs in the off cycle. There is some type of oil separator on the discharge line. Again they are different in design, but accomplish the same task. If the store has heat reclaim then the discharge has a 3 way valve that sends the hot gas to an evaporator in the air handler and then the condenser or just the condenser, routinely the low temp rack runs the domestic hot water preheater. The condenser is either air-cooled or water-cooled. Each rack is assigned a suction group. -25, +10, +15, +20 evap temperature and normally if there are coffins there is some type of ice cream satellite at -35. Hussman uses on their plus rack design 3 racks with a split meat satellite on their medium temp racks. Tyler normally uses a different rack for suction group. However Hussmann has an odd rack system TD that is very bizarre to work on, since the low temp rack discharges to the high temp rack. I've seen some amazing things happen to compressors when people forget to pump the low temp down first and recover last. Anyway I think I rambling, the long and short is, there is no "BOOK", or at least none I've seen, just what I call "corporate knowledge" and experience. Spend some time to trace out the lines and you can get info on the particular components and then put it together as a whole and you'll see, they work great and are pretty easy to work on. Especially if you have to work on a specific lineup. you can, for example take down the deli cases and keep the rest of the rack up. (I really like that).

    A pat on the back is nothing more then topical anesthesia for a knife.

  4. #4
    Originally posted by r22coolguy
    Tyler uses a balanced approach with an equalization line so that no compressor over fills. Hussman uses and expansion valve style with solenoids to prevent pump outs in the off cycle. There is some type of oil separator on the discharge line.
    What Hussman racks have the solenoid to prevent pump out?

    I think all racks I've seen have the reservoir with a rated check valve (5#,10#,20#) vented to the highest suction group to insure flow to all comps.

    Ones without reservoir (Superplus i.e.) have the oil valves you are talking about (txv) to drop pressure.

    We close off the equilization lines in case one comp starts pumping oil it will pump out the rest. Or if one has a pressurized sump for any reason it doesn't affect the rest.

  5. #5
    Join Date
    Aug 2002
    Location
    Orange County CA
    Posts
    1,084
    Some HL-80 racks I think

  6. #6
    Join Date
    Sep 2001
    Location
    East Stroudsburg, PA
    Posts
    13,215
    Originally posted by dum one
    can't seem to understand rack systems! need a sight or reading material for more of a understanding please.
    Ask specific questions here and we'll try to help.

    There is no actual text on this specialty yet.

  7. #7
    Join Date
    May 2004
    Location
    Ponchatoula, LA
    Posts
    84
    Jerry,
    The Hussmann Plus rack design uses a solenoid valve on the outlet or balanced side to prevent overfilling on an off cycle. The Plus has the separator in the discharge line the oil returns to the compressor through a drier and then a TXV to a main oil header that feeds individual compressors through a service valve. The equalization line also has a service valve, but also has a solenoid to prevent flow on off. Atleast every Hussman Plus I worked on is that way.
    A pat on the back is nothing more then topical anesthesia for a knife.

  8. #8
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    You probably know more than you think you know if you have a very deep understanding or a regular refrigeration system, built up type systems that stage and what not.

    Ask away. Some top notch rack guys on here and willing to help you if you'd like.


  9. #9
    Join Date
    Oct 2000
    Location
    St. Augustine, FL. USA
    Posts
    46
    The "TXV" you are referring to on a Hussmann rack for oil control is actually a pressure reducing valve, used to prevent pushing the oil floats open. It functions strictly to maintain a fixed pressure above suction pressure, hence the equalizing line to the suction manifold.

    A common problem with this valve is driers are used upstream instead of oil filters which in high demand does not provide enough oil flow, nuisance oil failure.

  10. #10
    Join Date
    Sep 2001
    Location
    East Stroudsburg, PA
    Posts
    13,215
    Originally posted by DrFreeze2000
    The "TXV" you are referring to on a Hussmann rack for oil control is actually a pressure reducing valve, used to prevent pushing the oil floats open. It functions strictly to maintain a fixed pressure above suction pressure, hence the equalizing line to the suction manifold.

    A common problem with this valve is driers are used upstream instead of oil filters which in high demand does not provide enough oil flow, nuisance oil failure.
    The Y1236C valve, which you refer to, is for use on high pressure oil delivery systems only, such as with a Hussmann "Turbashed". It is merely an adjustable pressure differntial valve, and will be effected by reduced flow of oil caused by plugged or undersized filters/filter-driers just like any valve for any type of system.

    I've seen 163 filter-driers used for many years on medium temp systems with Turbasheds and this valve, without any problems.

    The valve comes factory set at a 17 psi differential, and is only adjustable between 10 and 25 psi diff.

    I prefer SF283s and OF303s where possible, but this valves' main problem is that it's misunderstood by 80% of the technicians out there, thus gets looked at more often than it should. Long before, in fact, the system is really cleaned, which is often the root cuase of an oil problem.

  11. #11
    Join Date
    Aug 2004
    Location
    Nevada
    Posts
    179

    Thumbs up WOW

    123yc hehe, I dont remember anyone mention that valve, here in any prior conversation or reading it! I am not familiar with these racks, and i do find them interesting too! and I Enjoyed reading the full explanation of a basic system-in a nutshell. I think specifics could be asked if the system was already known- of course thats kind of redundent! so is there any books on rack systems out there or any video material to get oneself , familiar with? Ok here goes some questions, dont attack me for asking please , i dont respond well to that, Please!? I didnt exactly get the understanding of the oil returning to the compressors, if they do ,do they share a common oil return? as to the hussman 3-temp rack sytems? and if the , high temp rack is fed by the low temp discharge what is its intent and or purpose and what has to be done ? In recovering the low temp side, the high temp would have to be disabled to work on the low temp refrigeration circuit? what kind of metering devices do these cases and walk ins use aare they txv usually and the glass reachins? how do these ever satisfy and shut-off the compressors, wouldnt they ice up the coils, cause someone told me they run all day by a valve set at a on the rise that opens at a given pressure setting, what about the differential? and how does the compressors know when to stage on when the suction valve that is set for a rise in pressure- does that send a pressure control- that is also in the circuit connected to a compressor contactor?

    [Edited by 2seasons-employed on 09-10-2004 at 04:49 PM]

  12. #12
    Join Date
    Sep 2001
    Location
    East Stroudsburg, PA
    Posts
    13,215

    That's a lot of questions...

    Originally posted by 2seasons-employed
    123yc hehe, I dont remember anyone mention that valve, here in any prior conversation or reading it!


    That valve is specific to racks that have a combination oil separator/oil reservoir.

    "Conventional" (for lack of a better term) racks ill have an oil separator in the discharge header, which removes the majority of the oil from the hot gas as it leaves the rack. This oil separator has afloat valve in it that, when floating, opens a needle valve, and forces oil, under discharge pressure, to an oil reservoir. The oil reservoir has a check valve, with a set differential, between it and the suction header. This check valves allows the discharge pressure to bleed out of the oil reservoir, into the suction header, to maintain the oil reservoir at 10-20 psi above the suction header pressure. This differential is necessary to deliver oil to the compressor crankcases, through the oil level regulators (another float valve.) that are attached to the sightglass port of the compressor crankcase.

    The racks that use this this combination separator/reservoir (mostly Hussmann's proprietary "Turbashed-----Yes, that is the correct spelling.) are left under discharge pressure, and this adjustable differential check valve is placed in the oil feed line, leaving the Turbashed, going to the oil manifold/level regulators/compressors. It's purpose is the same as the OCV in the other system, except it is located in the oil line. It has it's own "vent to suction header" port, in addition to an inlet and outlet. It resembles a TXV, but is NOT a TXV, just an adjustable differential check valve.

    Originally posted by 2seasons-employed
    I am not familiar with these racks, and i do find them interesting too! and I Enjoyed reading the full explanation of a basic system-in a nutshell. I think specifics could be asked if the system was already known- of course thats kind of redundant! so is there any books on rack systems out there or any video material to get oneself , familiar with?


    None that I have ever seen. Lots of people ask this question, and so far no one has produced anything, just reasons why there aren't any texts available- Publishing costs and lack of demand.

    Ok here goes some questions, dont attack me for asking please , i dont respond well to that, Please!? I didnt exactly get the understanding of the oil returning to the compressors, if they do ,do they share a common oil return?[QUOTE]Originally posted by 2seasons-employed
    [/B]

    See above explanation.

    Originally posted by 2seasons-employed
    as to the hussman 3-temp rack sytems?


    Are you referring to the compound racks, or just a multi-temp rack? There's a big difference.

    Originally posted by 2seasons-employed
    and if the , high temp rack is fed by the low temp discharge what is its intent and or purpose and what has to be done ? In recovering the low temp side, the high temp would have to be disabled to work on the low temp refrigeration circuit?


    Yes, in a true compound rack, the entire system has to be on or off for it to work. Racks are rarely recovered. The charges are, by nature, large, and just about every component of the system can be isolated and serviced. Some with the system in operation, some require full system shutdown.

    Originally posted by 2seasons-employed

    what kind of metering devices do these cases and walk ins use aare they txv usually


    TXVs are the most common, but the newer systems often use electronic "stepper" valves, controlled by the DDC, to meter refrigerant.

    Originally posted by 2seasons-employed

    and the glass reachins? how do these ever satisfy and shut-off the compressors, wouldnt they ice up the coils, cause someone told me they run all day by a valve set at a on the rise that opens at a given pressure setting, what about the differential?


    Depends. Often, the cases don't "satisfy" at all, like on a conventional condensing unit, on racks. At other times they do.

    2 BASIC types of temp control:
    • SORIT (Or SORIT-PI): (Using Sporlan's nomenclature, because they are the only valve manufacturer that knows what they're doing...)
      The rack controller (Mostly DDC these days) is in place to maintain a target range of suction pressure on each suction manifold. It does this by cycling the compressors and/or unloaders that are attached to that header. The SORIT valves are UPSTREAM of the suction header, and downstream of the SYSTEM evaporator(s). Each evaporator pressure regulator is set, by pressure, to maintain a constant evaporator temperature for each system. This gives great flexibility to have a wide range of temps on each rack.

      These valves should only cycle electrically, in two circumstances:
      • During a defrost cycle.
      • When the "setpoint" is attained in the computer control.

      If the setpoint is reached, something is wrong, and needs to be repaired. These valves don't like to cycle electrically, and can wear fast when doing this.
    • Liquid Line Solenoid control:
      The LLS valves cycle on the controller temp setpoint. The rack controller again, tries to maintain a certain suction pressure by cycling the compressors/unloaders.


    [Edited by condenseddave on 09-11-2004 at 12:23 AM]

  13. #13
    Join Date
    Sep 2001
    Location
    East Stroudsburg, PA
    Posts
    13,215
    I ran out of room. More later. I'm tired.

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