Racks are simple! Right? ....
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  1. #1
    Let me get this straight .... most of my racks are ganged clocks with suction stops.

    So the temp in the cases is being controlled by the EPR valves. Then once the "Controller" sences the circuit is down to temp, it closes the the liquid line solenoid and suction stop solenoid valve and the compressor shuts off.

    Is this correct?

  2. #2
    Join Date
    Mar 2001
    Location
    Halifax, PA
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    187
    All depends on the rack, the store, most everyone just shuts down your suction stop, that way your not pumping out your whole circut when the system goes into defrost, or l.l solonid valves are installed at the cases and there shut down during defrost. and yes your temp in your cases is either going to be controlled by some type of epr valve, in smaller stores they use l.l.solonids with sorit valves on the racks. All small stores are set up alittle differently these days it seems.
    If you cant find the time to do it right the first time, then you wont find the time the second time around....

  3. #3
    Originally posted by bowman
    All depends on the rack, the store, most everyone just shuts down your suction stop, that way your not pumping out your whole circut when the system goes into defrost, or l.l solonid valves are installed at the cases and there shut down during defrost. and yes your temp in your cases is either going to be controlled by some type of epr valve, in smaller stores they use l.l.solonids with sorit valves on the racks. All small stores are set up alittle differently these days it seems.
    A few of the circuits have T-stats and ll solenoids. But most of the rack is made up of circuits which utilize suction stops and EPR valves.


    I guess I just do not have the sequence of operation down pat yet.


    I am not worried abot how solenoids operate or EPR valves. I am comfortable with those parts. I dont know the seq of ops nor the controller yet.

    All in due time I am sure.


  4. #4
    Join Date
    Sep 2001
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    East Stroudsburg, PA
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    Originally posted by R12rules
    Let me get this straight .... most of my racks are ganged clocks with suction stops.

    So the temp in the cases is being controlled by the EPR valves. Then once the "Controller" senses the circuit is down to temp, it closes the the liquid line solenoid and suction stop solenoid valve and the compressor shuts off.

    Is this correct?
    The ones I deal with use SORITS, SORIT-PI's, AND SPORT's, for the most part. Loops usually suck, er, use LL solenoids.

    With that actual genre of piloted EPR valves, no, they do not usually turn off electrically when the target temp has been attained. That would be the purpose of a standard solenoid valve. ("Suction stop, when applied in the vapor line...) EPRs should be set ONLY to maintain the required evap pressure, to obtain a desired evaporator/case temperature. They should only cycle off electrically automatically, in two instances:
    • A lower than desired temp is reached.
    • A defrost cycle is initiated.

    In fact, I believe that Sporlan doesn't want their piloted EPRs cycle more than about 4 times a day, although that might be erroneous information. (Andy Schoen can clear that up, I'm certain.) Excessive cycling of this type of valve does result in frequent valve failures, generally at inopportune moments...

    Suction Stop Solenoids would shut down electrically upon reaching target temp, or during defrost, as would Liquid Line solenoids.

    A problem with turning off a Suction Stop solenoid for a long period of time, without also closing a LL solenoid in the same line, is the possibility of backing up too much gas in a long run, which could starve the other systems, until that circuit called.

    A problem with low temp loops, which we frequently see, is with guys "turning down" the temps on a system or two to compensate for another problem, which makes that system stay on too long, which results in the following issues:
    • High suction pressure at the header from "too much" load.(More than the designer ever intended to be running at once.)
    • Low liquid conditions, because these things were set up with the INTENT that not all the systems would be calling at the same time, for very long. (All the gas is out in the system, rather than in the receiver.)

    Both of these will occur at the same time and will always result in a poor recovery rate.
    (Not part of your question, but I figure you'll be seeing that soon, too. Real common.)

    IE. If you see frozen waffle cases on a loop, set for -20 with 5 degree dead band, it's WRONG.

    Did I answer the original question?

    OOPS, Nope.

    Yeah, racks are easy. (So are earth girls, I hear. )


  5. #5
    So ... the rack is made up of several units all running on pressure controls to start and stop the compressors, as the controller deems necessary. Right?

    And temp is maintained in each individual case by the EPR valve. Correct?

    And when defrost occurs, the ganged clock will each one turn off a suction stop, which is a solenoid valve located in the suction line, next to the EPR valve. Right?


    As long as the header pressure is maintained within certain parameters, the controller cycles on and off each compressor as needed to maintain a predertermined suction line pressure. Right?

    If I can draw on a napkin a basic electrical schematic of the controls ... I can electrically troubleshoot it should a problem occur.
    And if I know in advance what the seq of ops is for the given system, I know I can be watching to see what is functioning correctly and noticing anything out of order.


    It's late, I'm pooped .... maybe I should simply turn in and re read everything said tomorrow.


    Thanks Dave and bowman .... it all helps form the picture I need to see.

  6. #6
    Join Date
    Sep 2001
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    East Stroudsburg, PA
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    When you speak of EPRs, Bob, are you talking about plain old ORITS, with no pilot solenoid on them???

  7. #7
    Join Date
    Feb 2003
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    Temp and defrost control can be done a lot of ways, not typical to see a system deenergize both the suction stop and liquid line solenoid at defrost or when desired temp is reached though.
    You have to go through the program and find out whether the system is "EPR" or "full temp" control.

    EPR control usually means the temp is controlled by the setting of the EPR and defrost is controlled by deenergizing either suction stop EPR (if so equipped) or liquid line solenoid.

    Full temp control usually means the the liquid line solenoid is being controlled by a temp set point and will be cycled by the refrig relay at a given set point.

    In your case with gang clocks, and no controller I guess they could be deenergizing both the suction stop and the liquid line solenoid during defrost, but I dont see a need for a suction stop type EPR, if you're already denergizing a liquid line solenoid.

    When your working with those Com-trol units sometimes you have to ignore that the controller has a temp. setpoint as it is meaningless if the particular circuit is setup to "monitor and alarm" only.

    Despite all the knocking of Hussmann I find they are pretty good at providing detailed electrical schematics affixed inside the rack panels that will tell you exactly how certain offtime or hot gas circuits are wired.
    On medium temp. systems they are leaning toward EPR control with suction stop EPR's that deenergize at defrost and no liquid line solenoid at all. I find this to be the most reliable way to control a system, had lots of problems when racks were put out with full temp control on every system.

    R12 did you checkout that access to Com-trol's BBS, I think it also has a simulated 4000 panel that you can download and play around with to familarize yourself with the controller, kinda hokey but tells you what all the buttons do.


    Watts New, Ohm My, I been Electrically Commutated. Are U2.

  8. #8
    Join Date
    Sep 2001
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    East Stroudsburg, PA
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    13,215
    Liquid Line Solenoid controlled fresh meat case graph:



    And then, a SORIT valve controlled meat case graph.


    Doesn't seem like too big of a difference, but those small swings in temp really add up over a few days.

  9. #9
    Join Date
    Sep 2001
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    East Stroudsburg, PA
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    Hmm

    I prefer the SORIT, of course, and of course, I pulled up a crappy example, but it's late and I'm tired.

    See you tomorrow...

  10. #10
    Join Date
    Jan 2004
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    Dave is right on the money with sorit not being able to handle alot of openings and closings.

    We tried a full strategy temp control with sorits and they would fail (leak) very quickly. Suction stops did a better job.

    The temp graph on these circuits was much flatter than EPR control. The energy monitoring showed lower consumption. I personally am not convinced this method is better.

    The compressors cycled much more freqently 10-15 times an hour compared to 2-3 times with EPR strategy. This would seem to be much harder on the comps, contactors.

    I believe it takes more more energy to start a compressor than to run it. Does any one know how the start kilowatts compares to run kilowatts.

    Dave, I think racks are alot easier than earth girls. They don't talk back, and they do what you tell them. Earth girls are more fun though.
    A Diamond is just a piece of coal, that made good under pressure!

  11. #11
    Join Date
    Apr 2002
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    Ann Arbor, MI
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    Originally posted by condenseddave
    In fact, I believe that Sporlan doesn't want their piloted EPRs cycle more than about 4 times a day, although that might be erroneous information. (Andy Schoen can clear that up, I'm certain.) Excessive cycling of this type of valve does result in frequent valve failures, generally at inopportune moments...
    Let's say that we would prefer not having our pilot operated EPRs operate in manner like the life cycle testing we perform in our engineering labs...

  12. #12
    Originally posted by condenseddave
    When you speak of EPRs, Bob, are you talking about plain old ORITS, with no pilot solenoid on them???
    I'll snap a pix on Monday. These have solenoids on them.

  13. #13
    Originally posted by condenseddave
    When you speak of EPRs, Bob, are you talking about plain old ORITS, with no pilot solenoid on them???
    Dave, I just dug up my Sporlan catalog. It shows a picture of my valves listing under (S)ORIT. PAGE 48 OF CATALOG #201.
    There IS a solenoid on them.


    Thanks.

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