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  1. #1
    Join Date
    Jun 2011
    Posts
    9

    Adjust an EPR w/o a pressure tap?

    I am new to refrigeration and have nobody i work with to ask questions....

    that being said i am working on a piece of equiptment and it has a TXV,EPR,a liquid injection valve, and hot gas bypass. i have replaced the txv, and liquid inj valve, and i am now trying to get the thing tuned in, but am having troubles... one of my questions is what do i set my EPR to and how do i set it without a pressure tap on it? thanks guys, you help would be very much appriciated

  2. #2
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,918
    Cut one in.

    ONLY way to do it accurately.


    You are describing a low temp system. Are you SURE it is an EPR? It could be a CPR which CAN be accurately set without gauges.

  3. #3
    Join Date
    Jun 2011
    Posts
    9
    pretty sure its an EPR. it is located downstream of the evap coil, but before joinin the liquid injection on the suction line.

  4. #4
    Join Date
    Jun 2011
    Posts
    9
    it is not a low temp system, this is a stability chamber that must run between 0*c- 100*c

  5. #5
    Join Date
    Jun 2011
    Posts
    9
    my mistake, i looked up the part number and it is listed as a CPR.
    so i adjust this so the compressor will not draw more then RLA on startup?
    anyone know the order in which the components txv,liquid injection and cpr should be adjusted?

  6. #6
    Join Date
    Apr 2012
    Location
    Northern Virginia
    Posts
    30

    Wink EPR v/s CPR v/s MOV expansion valve.

    Yes I do. A CPR valve is in place to do nothing more than ensure the compressor doesn't overload on a hot start after defrost. An EPR valve is there to maintain a certain evaporator pressure so the coil won't drop it's saturation temp too low and freeze. It does this by flowing high temp gas into the evaporator coil, again, to maintain evaporator pressure. And finally you're hard shut off TXV or MOV valve as you call it does nothing more then to prevent the system from equalizing completely during an off cycle. It really is only there to ensure as soon as the system does start back up there is a solid column of liquid already at the inlet of the TXV so we don't have and starved compressor starts.

  7. #7
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,918
    Quote Originally Posted by EZE2489 View Post
    Yes I do. A CPR valve is in place to do nothing more than ensure the compressor doesn't overload on a hot start after defrost. An EPR valve is there to maintain a certain evaporator pressure so the coil won't drop it's saturation temp too low and freeze. It does this by flowing high temp gas into the evaporator coil, again, to maintain evaporator pressure. And finally you're hard shut off TXV or MOV valve as you call it does nothing more then to prevent the system from equalizing completely during an off cycle. It really is only there to ensure as soon as the system does start back up there is a solid column of liquid already at the inlet of the TXV so we don't have and starved compressor starts.
    An EPR valve does not do this.

  8. #8
    Join Date
    Apr 2001
    Location
    Over Here
    Posts
    1,105
    An EPR valve does not use hot gas to regulate evaporator pressure. That is a hot gas bypass valve that does that. It introduces hot gas into the low side usually at the distributor nozzle to maintain velocity through the evap coil for proper oil return.

    An EPR just maintains a pre-determined pressure in the evaporator coil at the outlet of the coil. They are usually used when there are evaporators tied in the same circuit with differing saturation temperatures.

    A CPR works similarly, but opposite to an EPR.

    Remember, an EPR regulates pressure before the valve, and a CPR regulates pressure after the valve.

  9. #9
    Join Date
    Feb 2005
    Location
    In a van by the river
    Posts
    621
    Yes, as mentioned above, think of an EPR as an inlet pressure regulator and a CPR as an outlet pressure regulator.
    ## + years in the field never made you a know-it-all This industry is far more diverse than you are

  10. #10
    Join Date
    Oct 2009
    Location
    Raleigh, NC
    Posts
    800
    I used to work in a few supermarket motor rooms that had hot gas operated EPR valves on the suction branches. They didn't inject any hot gas for controlling evaporator pressures, but they did use hot gas to actually operate the valves. There were hot gas headers running down right next to the suction headers.

  11. #11
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,918
    Quote Originally Posted by MicahWes View Post
    I used to work in a few supermarket motor rooms that had hot gas operated EPR valves on the suction branches. They didn't inject any hot gas for controlling evaporator pressures, but they did use hot gas to actually operate the valves. There were hot gas headers running down right next to the suction headers.
    Yes.

    Sporlan SORIT valves and Alco BEPRS valves both use high pressure gas for closing force.

    The pressure actually bleeds out downstream of the valve, though.

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