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  1. #1
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    Pressure control



    Hello guys, I'm still studying for my R290 cold trap project. Some have advised me that I could implement low pressure and high pressure controls for improve safety measures. However, I have hard time even finding a supplier for those items, and besides I've never seen a small appliance with R290 or R600a, which uses a capillary tube, fitted with high or low pressure controls. Ideally, I'd want the low side to not go below 0 psig, and the high side to mantain its optimal values considering a condensing themperature of 35-40 įC. If I recall correctly, there is a physic law, called the ideal gas law, which states that pressure and temperature of a gas should have a direct proportion. I was thinking that I could stick two thermocouples and have a microcontroller to halth the compressor in case the themperature of the vapour and liquid line go over a threshold. I can define this threshold using the R290 pressure chart or by measuring the themperature of the copper pipes while I still have my pressure gauges on so I'll know what themperatures are correct. Are my assumptions correct or is there something blatantly wrong with my understanding?
    Thanks everyone!



  2. #2
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    Re: Pressure control

    kay86,
    If you have superheated gas, or subcooled liquid then laws of pressure & temperature do not work.
    You could use Danfoss dual HP/LP pressure switch , simple as you can get.
    Calibrate switch using gauges etc with notrogen, don’t rely on scale of switch.

  3. #3
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    Re: Pressure control

    Quote Originally Posted by RANGER1 View Post
    kay86,
    If you have superheated gas, or subcooled liquid then laws of pressure & temperature do not work.
    You could use Danfoss dual HP/LP pressure switch , simple as you can get.
    Calibrate switch using gauges etc with notrogen, donít rely on scale of switch.
    Thanks Ranger,
    The problem is that R290 is a flamable A3 class refrigeration and I should not use flanged joints, so I would need a sensor that can be brazed on the circuit. That's basically my problem, I can't seem to find anything specific for R290 and brazed joints.

  4. #4
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    Re: Pressure control

    I found this:
    https://store.danfoss.com/en/Climate...5/p/060-001066
    It would be perfect, too bad that the manufactor didnt include R290 or any other A3 gasses in the list of allowed refrigerants.
    If you guys know of any alternative, I would be very thankful.

    On a side note, I would be interested in understanding what are the circustances that could cause an abnormally high head pressure. I could think of clogged condenser fins, so it overheats and the pressure increases, or maybe clogged capillary so the refrigerant flow is restricted, right? But in these events, woudn't the power consumption of the compressor increase aswell? So what if I closely monitor the power consumption of the compressor while still having the low and high site manifolds attached so I can chart the power consumption and have a controller to halt the compressor if it works too hard? Ideally it would be better if I found a correct pressure control to install, but in case I cant find any?

  5. #5
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    Re: Pressure control

    kay86,
    Lots of new equipment, must have some sort of protection made by someone.
    This is something I found, but not involved in this area.

    https://climate.emerson.com/document...gb-3842854.pdf

  6. #6
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  7. #7
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  8. #8
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    Re: Pressure control

    Thank you guys, I appreciate it.
    As Sean suggested, it was just a matter of selecting the correct filter for ATEX cat3 refrigerants on the Danfoss site.

    I think I may be able to get both the high and low pressure switches for 300 euros which I understand it's not a trivial amount of money but since I'm setting up this system from zero and I don't have much experience, I want to be as safe as possibile. I understand that, for example, the blast freezer I own doesnt have any pressure control, and it works with R290. However this product was designed and produced by a respectable company so I assume they designed it properly, altough I understand that they could not factor in the cost of the sensors. On the other hand, I could design my system with a slight shorter or longer capillary, or with a not properly sized condenser or evaporator. So, even if I am reading correct values of temperature and pressure on my Testo gauges during the testing process, I assume that something can go wrong in the following months or years so I am considering this as a correct investment. Do you guys think that this is a good investment or I could just do without them since it's "just" a 2 oz R290 application?

  9. #9
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    Re: Pressure control

    installing the pressure switches further away form the refrigeration circuit, with long capillary tubes, isn't that a possible solution?
    Installed inside or outside and what charge?
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  10. #10
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    Re: Pressure control

    Dear Kay86. Some years ago my company bought to Intarcon company (at Spain) a refrigeration unit (compresor, receiver, condenser, plate exchange to cool glycol and electrical switch board) working with R290 (propane) to maintain a pressure inside the R744 vessel that cannot be bigger than the maximum admissible pressure on the R744 plant. This would be useful in case for example of the main energy cut out for long time.

    You can talk with INTARCON to see if the can help you in some how.
    Last edited by Sandro Baptista; 21-03-2023 at 01:38 PM. Reason: forget to add thing
    To make progress is never good enough, I want to do better and better and better

  11. #11
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    Re: Pressure control

    Sorry, I'm waking up. I also have a product of the Suntec brand. I am having similar issue. I think there is an electrical problem. How can I overcome the problem?

  12. #12
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    Re: Pressure control

    Pressure control is an important factor in many industries, such as manufacturing and engineering. It involves the regulation of pressure levels to ensure that they remain within a certain range for optimal performance. This can be done manually or with automated systems, depending on the application. Properly controlling pressure helps maintain safety standards while also ensuring efficiency and accuracy in operations. Additionally, it allows businesses to save money by reducing energy costs associated with operating machinery at higher pressures than necessary.

  13. #13
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    Re: Pressure control

    Amazing information

  14. #14
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    Re: Pressure control

    Did a robot just compliment itself on a nice post? This chatgpt business may be going too far...

    MrFreeze

  15. #15
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    Re: Pressure control

    Could be but I doubt that a robot registered as 'josephmack'

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