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  1. #1
    Join Date
    Apr 2012
    Posts
    6

    NH3 Compressor dumping its oil

    We have an NH3 350 HP. FES twin screw Model 19-L, Serial 19L96-V. The compressor will dump its oil from time to time. Generally if the suction gets low and the head pressure stays about or above normal. (Any thing below 20 on the low side and 150 or higher on the high side) we will also see problems if the head gets to high 180 and up, and the suction stays about normal (28-32). We have talked to numerous people who all say the same thing it is a "Design flaw" Basically they are telling us the way the compressor was built and set up the oil seperator (large tube under the motor and compressor) where the coilecent filters are is to small for the size of compressor. My question is, has any one ever seen this before, if so is there ANYTHING at all that we can do besides get a new compressor. We are currently in the process of replacing two compressors as it is and would like to keep this one if at all possible. For now, the option that we are going to look at is a low and high shut down so we can unload the compressor before it pukes all of its oil out. (When it decides to do so this happens within seconds and it is all gone.) Any input would be greatly appreciated!!!

  2. #2
    Join Date
    Feb 2010
    Location
    NE Alabama
    Posts
    301
    So many questions. Since this is a sealed system where is this oil being dumped to? How is this system setup? Condenser on the roof, and evap on a lower level? Refrigeration and ice systems have oil sent through the system as part of normal operation, and if the system isn't correct the oil leaving won't make it back to the compressor.

  3. #3
    Join Date
    Apr 2012
    Posts
    6
    The Oil gets pumped out of the compressor and through the system. We recover what we can in the oil pots throughout the plant. Condersor on the roof. All evaps are one story down from the compressor that is dumping. As a normal operation we do not pump oil throughout the system.

  4. #4
    Join Date
    Feb 2008
    Location
    California
    Posts
    2,071
    If the oil is not being separated from the discharge vapor. I gotta assume your separator isn't doing its job. Have you guys checked the coalescing element's?
    Last edited by Phase Loss; 05-17-2012 at 01:57 AM.

  5. #5
    Join Date
    Apr 2012
    Posts
    6
    We change the coilecent filters about 2 times a year or whenever it blows the oil out.

  6. #6
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,483
    This is a tad outside my bailiwick, but screws are oil injected by design and therefore require a very efficient oil separator to remove all the oil before it goes out to the system. The coalescent filter is probably the best at this.

    Another point, which I'm not sure how it applies to NH3 or coalescent filters for that matter, is my limited experience with R22 screws tells me they need to maintain a minimum discharge superheat for proper separation.

  7. #7
    Join Date
    Dec 2010
    Location
    Savannah Ga.
    Posts
    42
    I'm not sure if this will pertain to your problem, but years ago I dealt with a similar problem involving compressor oil loss on a Vogt P-24 ammonia ice maker that caused many sleepless nights and took us forever to figure out! Our machine had a Mycom reciprocating compressor and not a screw for what it's worth. In our case the problem would only occur within the first 20 minutes after start up when it had been shut down for numerous hours, which of course leads you to think the crankcase heater is not functioning, but it was. Once we got it going, it would operate problem free until the next time we shut it down for several hours. We noticed that before start up, it had proper oil level and the compressor belly was nice and warm from the heater running, but shortly after starting the oil would become cool and foamy and would start dropping pressure. We knew we were dealing with an overfeeding issue that only occured at start up? In the end, what we found was that we had too much moisture (water) in the system. Anhydrous ammonia reacts quite violently with water and if you get enough stuck in the evaps, the violence of the reaction will cause an excess of liquid ammonia to "slopover" out of the evap and head to the compressor, which will foam the oil and chase it out of the compressor faster than the oil return can return it. To find out if this is your problem, you have to pump down the low side to zero pressure which will allow the water to seperate from the ammonia and settle to the bottom of the evaps. After that, open up the drains on the catch pots at the bottom of the evaps and catch it in buckets to see what you've got. Unless you are able to let it sit awhile pumped down, there will be oil mixed in with the water. It doesn't take a huge amount of water to cause problems, we probably had about 1 or 2 gallons in a system that holds 800 lbs. of ammonia. Again, this may not be your problem, but may be worth looking into!

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