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Kool Gas Defrost liquid differential.

Discussion in 'Refrigeration' started by Dowadudda, May 10, 2011.

  1. Dowadudda

    Dowadudda Staff Member

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    :bs:when setting kool gas defrost liquid differential valve, should you set it and actuate it with out anything in defrost or with a circuit in defrost. I have been taught the 2 different ways, and I don't see any damn difference.

    Today this came up and I just don't see the arguement. Plus I did do it both ways today and I witnessed no difference. But, I have people telling me that there way is correct.

    What say you?
  2. Mcool

    Mcool New Member

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    4D welcome back
  3. jpsmith1cm

    jpsmith1cm Professional Un-thawer

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    I set with no systems in defrost.

    I also have tried it both ways and haven't seen a significant difference.
  4. frozensolid

    frozensolid Psychologist's Dream

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    I tried to find the sporlan instructions but I had no luck. I believe these valves to be of the modulating type so how could it possibly make a difference?

    The only reason I could even possibly imagine for having to have a system in defrost is if the valve had a minimum inlet pressure requirement. Then maybe they wanted to be sure it had that in defrost.
  5. crackertech

    crackertech assholiness

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    X 3 either way works for me.
  6. Dowadudda

    Dowadudda Staff Member

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    thats settled. thanks guys.
  7. 10"DrainLeg

    10"DrainLeg New Member

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    I believe it is a little more accurate to set the valve while no systems are in defrost. With no systems calling for gas defrost, the header is isolated and you will see adjustments rapidly. However if you adjust it while a system is in defrost, there is a demand for defrost gas and depending on how large of a lineup and how far of a run. I believe that could cause the differential valve to respond rather sluggish to your adjustments and possibly leave you with an over or under adjusted differential.
    somedude likes this.
  8. Dowadudda

    Dowadudda Staff Member

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    I am a pretty experienced refrigeration man. I got that way by questioning things, I am kinda a guy that has to be proven to, shown to me when I oppose what the theory is. Since I want to know, and since I have to get this out of my system I prove it to myself.

    This was a question I posed due to my own brain not wanting think as taught. I went and screwed with a few different racks and different set ups, and I now will forever do it your way from here on out. I promise.
  9. 10"DrainLeg

    10"DrainLeg New Member

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    GOOD! :beer: I may be going to Texas and don't wanna re-adjust a bunch of differential valves :p
  10. Dowadudda

    Dowadudda Staff Member

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    Well come on.
  11. otto

    otto Bakery Chef

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    Back when I was new in this field I always asked lots of questions and still do. It got under the skin of some of the people who I would ask, maybe they didn't know the answer. I took apart pumps and gas valves, fan & limit controls, etc. It has definitely made me a better technician.
  12. 10"DrainLeg

    10"DrainLeg New Member

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  13. Dowadudda

    Dowadudda Staff Member

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    so, we talk a lot about technicians making the mistake that kool and hot gas defrost is accomplished by the gas condensing in the coil to achieve the ice melt needed. It's not about the heat content of the gas. We want change of state. Latent Heat of Condensation. So we acheive this by differential.

    I have a store I was at a few weeks back. Rack on roof. FF Glass Drs on sales floor. We as a company have a standard of 30 psi differential set on the actuating valve on the rack. This rack has a querky issue where if you set the differential at the rack for 30, and you put one of the RL line ups through a defrost, the defrost is incomplete. I have witnessed this with my own eyes. And you can see the this differential all day long standing on the roof at the rack. And then you can go to the cases and your not seeing the defrost occuring like it should, nor can you see the return liquid line temp rise to Saturated temp in case.

    You have to raise the differential to 40 to get this thing moving. And the only thing I can think of is, that piping and risers are dead heading my flow somehow and I just can not measure that due to lack off access and such. At 40, them coils clear, I get nice saturated liquid return temps quick and were off and running.

    It has to be some piping anomally. Somehow, were getting pressure drop through liquid lines. In order for me to see a PSI differential on rack at roof during a defrost, yet not have the differential at the cases to get me my gas moving, but when i raise that differential high enough I do get it, it's got to be a piping thing right?
  14. 10"DrainLeg

    10"DrainLeg New Member

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    88
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    California
    Sometimes you may need a higher differential when the rack is on the roof.

    Liquid is heavy

    The condensed defrost liquid has to travel reverse through the liquid line back to the rack. And depending on how large the line ups are and far the cases are from the rack and how high of a vertical lift that liquid must travel to get back to the rack.

    At 30 PSID there just may not be enough push to get that liquid moving out of the coils and back up to the roof.

    It's hard to put a fixed setpoint on something like defrost differential and gas defrost durations. Because there are too many different variables that just wont work in every situation.
  15. Dowadudda

    Dowadudda Staff Member

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    it's been a situation where I have had to go reset this thing several times in the last year, due to our guys being trained on 30, and they see a defrost issue, they check the valve and see it set higher, maybe for no reason but to check it and reduce the setting because they know it to be right at the 30 psi setpoint. I wrote 40 on it the first time, left a note in log several times. No one reads my stuff. I left a note this time, in a ziplock bag, tie wrapped to the valve stem, with a sharpie message on the front of the plastic "read first".

    I am still not convinced at why I need it higher. You have the same thoughts I have had before, but then I change my mind too.

    Dig this.

    I hear what your saying on weight of the refrigerant climbing up. But. (here is my brain thinking again), differential is differential. If I am seeing on the roof that differential, why is it not flowing. I do get it your thoughts, but then I don't.

    I am sending out say 150 (Hypothetical numbers) and the return is 120. I am basically reading both sides up at the roof. Should be the same down there.

    I got 150 up top, I have to have 150 into the coil, it condenses, as it leaves it has to be a lower pressure. If that liquid does in fact start to climb the rise, and the liquid starts it's route up the rizer, and it slows, slows slows, till it falls under it's own weight, the 150 would increase, and the 120 would increase. It can not be the same anywhere in that circuit in that state of movement. The pressure is transferring either way, upstream and downstream in unison, but all the while maintaining differential.
  16. 10"DrainLeg

    10"DrainLeg New Member

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    Location:
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    I can see the pressure sending out at 150 and retuning at 120, as the liquid climbs the riser, it falls under its own weight. Then we get the liquid just kinda sitting there...at that point, I don't see the inlet pressure start to rise above 150. The setting of the valve is 30 PSID and the weight of the sitting liquid is equal to or greater than 30 PSID. Any pressure increase above the 30 PSID setting on the inlet that's created by the sitting liquid would just bypass the differential valve and head on to the condenser or liquid header (depending on were you're creating your differential)

    If this is a kool gas defrost with a liquid differential valve. I wonder if an "Parker A82B" valve installed in the discharge line would help. It would be used in conjunction with defrost as a "bump up" valve and artificially raise the compressors discharge pressure when a system is in defrost. Then have a receiver pressurization valve feeding that artificially raised pressure onto the top of the receiver to assist in "pushing" that liquid out of the coils and riser.

    We have 1 store that does this. But it would be easier to just run a 40 PSID if that's what it takes to push the liquid out and get it flowing.
  17. Dowadudda

    Dowadudda Staff Member

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    Oh crap, forgot to mention. The rack has a disharge regulator too. It was not tied into the ro point until I first looked at the rack last Feb. Thats just for head pressure shift during defrost old school.

    If down inside the rizer where the liquid becomes heavy enough under it's own weight to become equal to the 30 PSI lesser on the liquid header it is on it's way to, downstream of that point, your saying, were saying it dead heads. I buy into this, but I also have reservations. Differential is Diferential, it has to flow. That returning liquid is moving to the header, all my other loads are using liquid from the header, being supplied by my defrosting line up, it has to flow. It's not gonna get jack from upstream of my actuated liquid differential valve. I know it doesn't at 30, but my brain makes me question why.

    40 makes it work. It's cool.

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