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Thread: CPR valve?

  1. #1
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    Confused CPR valve?

    Does the air conditioning system have a CPR valve? I know CPR valve is an option in refrigeration system, but have no idea whether it is necessary in vehicle A/C or home used A/C system.

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    CPR could be Crank case or condenser. Both typically only used in refrigeration.

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    Quote Originally Posted by ehsx View Post
    CPR could be Crank case or condenser. Both typically only used in refrigeration.
    Condenser pressure regulator?

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    Used in refrigeration during start-up to limit compressor load. Basically a hgbp from discharge to suction.

    Some units have also used discharge regulators to insure minimum differential between suction to discharge to insure oil feed.

    The teminology varies some with application & mfg.

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  8. #6
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    Quote Originally Posted by ehsx View Post
    Used in refrigeration during start-up to limit compressor load. Basically a hgbp from discharge to suction.
    You are correct in that a CPR is used to limit compressor load, however it is not done by hot gas bypass (HGBP). The CPR is simply a pressure regulating valve installed in the suction line upstream of the compressor which throttles closed on a rise in outlet pressure...ie, compressor suction pressure.

    The CPR is used to limit compressor suction pressure not only at startup, but for post-defrost and during hot gas defrost as well.

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  10. #7
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    Head master valves are a form of condenser pressure regulators. Industrial low temperature refrigeration will also use compressor by-pass valves to limit pressure ratio during start-up and pull down. In both cases the discharge/suction differential determine position. Both by-pass hot discharge gas.

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    The campus I maintain has walk-in cold rooms for research which maintain within 1 degree celsius. These rooms never shutoff, and use a hot gas bypass (compressor discharge) to create a false load. This hot gas is also used for the defrost cycle. We have CPR (crankcase press reg) valves on every room to protect the compressor from the higher pressures since the discharge gas is going straight into the suction side. As others have stated, this is specialized and you wouldn't need it on a residential system or a vehicle.

  12. #9
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    Quote Originally Posted by ehsx View Post
    Head master valves are a form of condenser pressure regulators. Industrial low temperature refrigeration will also use compressor by-pass valves to limit pressure ratio during start-up and pull down. In both cases the discharge/suction differential determine position. Both by-pass hot discharge gas.
    I agree that terminologies can vary, You're correct in what you describe, but I have never heard of any type of condenser pressure control referred to as a CPR valve, either in engineering, the trade or by a manufacturer.

    As an example of acceptable variants of terms, a Crankcase Pressure Regulator (CPR) and a Close on Rise of Outlet (CRO) pressure regulator are descriptions of the same valve, but CPR is the more specific of the two and would the preferred terminology. To use the term CPR for completely the different applications which you describe leads to confusion and errors in communication and so should be avoided.

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    I agree. Do a internet search "condenser pressure regulator" and see what comes up.

    ASHRAE Terminology official manual, " C.P.R. valve suction-pressure regulating valve". No official acronyms or abbreviations for HGBP EXV, TXV or many of the other commonly used. Not sure why they use periods on E.P.R. & C.P.R., but not on any others?

    This trade can be confusing. How many names for evaporators, condensers, ecomizers? When rewriting a technical manual, bolt & screw terminology became a big deal. A lot of the terms in older literature were vendor (e.i. "ferry bolt") or trade names rather than generic.

  14. #11
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    In my copy of "HVAC/R Terminology"- A Quick Reference Guide by Richard Wirtz, 364(+-)pages.
    CPR is the suction inlet of comp load controller.

    It sure is easy to "TRY" and slip your own wording/phrase into a discussion and everyone will instantly know how smart and Professional you are.


    I seem to remember me always being a little daffy in the head. I get confused easily. I like Professional wording,terms/phrases/slang that is clear and to the point. So, for some reason I have to ask a Q , A could be/might be/maybe/ is better than an "it is"? It is a Crankcase Pressure Regulator, IT IS a HGBP. It is a HeadMaster. KindaSorta like that.

    I learned many Blue Moons ago, when conversing w/ Engineers. They responded well/better when I tried as hard as hell to talk like them and use "their wording" once they have said it to me.

    Carrier Factory Service Instructors beamed with pride when we students used their wording.

    Copeland Factory Instructors drooled a little when we students imitated them.




    CPR is referred to the comp suction inlet press regular.

    It is a Good Read (reference-like a Dictionary)
    Last edited by TechmanTerry; 07-06-2020 at 11:35 AM.

  15. #12
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    I can be a speed-reading idiot sometimes. I read your question as containing: EPR <g>

    You can disregard all of the below. <g>

    In a properly specified and installed and balanced and maintained Single Zone AC system an EPR valve is redundant.

    But as a way to make an AC system perform outside of it's normal performance envelop - or to compensate for a lack of the first four things I mentioned - a EPR valve can be used to easily resolve some issues.

    I have used them with almost certainly more frequency than most and install one on All damper-zoned DX systems.

    I am going to install one in a week or two because . . . . the 3.5 R-22 outdoor unit is screaming it's way through it's third compressor in eight years. And the rubbish duct 'system' is in the 175Ί attic space. <g> The elderly unhealthy occupants cannot be without AC for more than a few hours. And I have a 4 ton R-22 condensing unit. So I am going to slam it into their place - despite the 90Ί weather - with an EPR valve - and let it fly. The EPR will then adjust the compressor capacity to match the heat loading from the evaporator. Plus; I will be able to run wherever evaporator temperature I want.


    PHM
    ---------------




    Quote Originally Posted by guchen View Post
    Does the air conditioning system have a CPR valve? I know CPR valve is an option in refrigeration system, but have no idea whether it is necessary in vehicle A/C or home used A/C system.
    PHM
    --------
    The conventional view serves to protect us from the painful job of Thinking

  16. #13
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    Quote Originally Posted by TechmanTerry View Post
    In my copy of "HVAC/R Terminology"- A Quick Reference Guide by Richard Wirtz, 364(+-)pages.

    It is a Good Read (reference-like a Dictionary)
    Problem is getting everyone to uses the same book. ASHRAE book is only 140 pages and is supposed to be the industry standard. I remember when R-400 series refrigerants were being promoted in the early '90s, they had no definition for heat exchanger approach with a refrigerant glide, just found a 2006 email correspondence with ASHRAE where they were finally trying to settle on an official definition. Copeland was not using the same standard of most refrigerant manufactures at that time & ARI also was lacking information.

    So wonder why so many systems were set up improperly or misdiagnosed. How much refrigerant is wasted because of lack of information on fractionalization?

  17. #14
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    A CPR valve prevents a high suction pressure from overloading the drive motor of a low temperature compressor.

    Lower pressure refrigerant has lower suction vapor density. So pumping it's volume requires big pistons. But less physical work is being done so the drive motor HP can be less. This fact creates the possibility of overloading the drive motor with excessive suction pressure. A CPR valve gets set to throttle the suction gas pressure which creates the rated FLA of the drive motor.

    An AC compressor is designed for pumping a high suction pressure - and has the (relatively) larger HP motor to accomplish it - so the motor cannot be overloaded. So a CPR serves no purpose on a high temperature refrigeration compressor like AC uses.

    PHM
    ---------


    Quote Originally Posted by guchen View Post
    Does the air conditioning system have a CPR valve? I know CPR valve is an option in refrigeration system, but have no idea whether it is necessary in vehicle A/C or home used A/C system.
    PHM
    --------
    The conventional view serves to protect us from the painful job of Thinking

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  19. #15
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    My Carrier Service Training" -ACH&R Dictionary, by Timothy Zurick,1977 version, Pages A-Z. Says the same thing,suction of comp.

    It is a Good Reference Read.

  20. #16
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    Thread Starter
    Quote Originally Posted by pecmsg View Post
    Condenser pressure regulator?
    Crankcase pressure regulator

  21. #17
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    Quote Originally Posted by icemeister View Post
    You are correct in that a CPR is used to limit compressor load, however it is not done by hot gas bypass (HGBP). The CPR is simply a pressure regulating valve installed in the suction line upstream of the compressor which throttles closed on a rise in outlet pressure...ie, compressor suction pressure.

    The CPR is used to limit compressor suction pressure not only at startup, but for post-defrost and during hot gas defrost as well.
    so where is it installed in a refrigeration system? in the evaporator?

  22. #18
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    I have searched online and found a picture. it shows that the CPR valve is installed in the evaporator.

  23. #19
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    Anywhere between the evaporator and the compressor

  24. #20
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    Quote Originally Posted by guchen View Post

    I have searched online and found a picture. it shows that the CPR valve is installed in the evaporator.
    I can’t see those numbers but that might be an EPR
    evaporator pressure regulator

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