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  1. #53
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    Quote Originally Posted by Boiler Guy View Post
    Vacuum pumps. I was surprised when the instructor for the Daikin centrifugal class suggested using only a 5-10cfm pump for evacuation. What kind of vacuum pumps are typically used? I’m sure the bigger the get the bigger the vacuum pumps get.
    All I use is a 10 cfm on everything. JMHO
    To much work with too little time!!!!

  2. #54
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    Im guessing it was low on oil, probably buckets of it laying around. Chiller shouldn't start till 110 net psi oil pressure.
    Quote Originally Posted by kmuchnick View Post
    Hi,
    I have a WDC-126 with Microtech II with a 4160 volt compressor (FLA 119amps). We have been having issues with high suction surge trips. Recently, after witnessing the guidevanes hung up while unloading we raised the net oil pressure from 80psi to 110 psi. While running both compressors at approx. 60-70% compressor 2 tripped on "low oil delta psi" which is oil feed pressure is less than evaporator pressure (setpoint at 40psi). The alarm logshowed feed pressure at 27 psi and evap. psi at 32 psi. It was also noted, that the oil resevoir had previosuly been in the top of the sight glass and after the trip it the sight glass was empty and the oil carried over to compressor #1. Upon insopecting the oil system we found a oil pump terminal strip that was overheated (tight connections) and equalized the resevoirs. Upon starting the compressor we found that the rotor was locked up. The current went to 522amps and stayed until we shut it off. My question is why did the oil pressure drop and need to be raised? Could raising it of caused or hid other issues? Why didnt the controller trip on low net oil psi? Why didn't oil rundown system lubruicate the bearings on coast down? Also, if it tripped on low oil delta psi prior to locked rotor I would of assumed it would of been a hard shutdown causing starter to trip? I am trying to wrap my head around why/how this happened and why the control system did not protect it. I would assume other sites have seen similiar issues. Any help would be great. Thanks in advance!
    To much work with too little time!!!!

  3. #55
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    Apr 2012
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    Quote Originally Posted by Tech Rob View Post
    I've never seen a chiller surge because the condenser water was too cold. Surge is caused by the lift pressure, which is dictated by the thermal lift, exceeding the capacity of the compressor at a specific speed/refrigerant flow rate. Cold condenser water causes a low lift condition which can result in a whole litany of other problems including but not limited to: oil loss/poor oil return, loss of motor, drive, and oil cooling, failure to load, failure to purge out noncondensibles, etc.
    Yes,a low end surge, as I used to hear it referred to. which actually means the chiller is in stall. Can sound like a bad bearing or marbles if it is a an older York YT low pressure chiller. Its nice if the particular plant has spares sensors or transducers for checking against if concerned about a reading. Too cold cond water can have similar affect in that the low load conditions involved affects both heat exchangers. evap section due to relatively light load from a cool building envelope and condenser because the lack of sufficient heat build up/transfer from the overall process. good questions Boiler Guy, keep'em coming as we all like to share here when we can.

  4. #56
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    Quote Originally Posted by Bklyntek View Post
    Yes,a low end surge, as I used to hear it referred to. which actually means the chiller is in stall. Can sound like a bad bearing or marbles if it is a an older York YT low pressure chiller. Its nice if the particular plant has spares sensors or transducers for checking against if concerned about a reading. Too cold cond water can have similar affect in that the low load conditions involved affects both heat exchangers. evap section due to relatively light load from a cool building envelope and condenser because the lack of sufficient heat build up/transfer from the overall process. good questions Boiler Guy, keep'em coming as we all like to share here when we can.
    The problem causing the surging in your example is a load that is too low to support the chiller's minimum load requirements. It may be exacerbated by colder CW, but not explicitly "caused by". If you were to raise the CW temp in this case, the surging would get worse, not better.
    The key to happiness is lower expectations.

    Don't pick the fly crap out of the pepper.

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