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  1. #1
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    Evacuation in Australia



    I have been evacuating a large chiller in Australia, monitoring the vacuum over a couple of days. The vacuum rises during the day but falls at night. Not sure if the heat of the day is causing moisture to evaporate faster or if the heat is causing the pipe work to expand and contract. Anyone else had similar experiences?



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    Re: Evacuation in Australia

    Allrounder,
    Is water or a lot of moisture expected in chiller?
    In some cases applying extra heat can speed things up like heat lamps or electric blowers.
    Ballast open on vac pump in the beginning, to deeper vacuum first up not the best either, as can freeze water.
    A good leak test first with high pressure dry nitrogen helps eliminates vacuum problems
    as well.
    What you say could be possible, what procedure are using.

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    Re: Evacuation in Australia

    Hi I am removing what was free water and is now moisture. I am now pretty confident that the heat of the day is causing a higher evaporation rate inside the system, I had 500 microns this morning rising to 1400 microns this afternoon.
    I am English so not used to evacuating in this kind of heat, I feel pretty confident the system will be dry in a day or so. My plan is to vac down to 250 microns and make sure the chiller will hold 1000 microns for 6hours. Then charge

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    Re: Evacuation in Australia

    To help you dry out the system, get a bottle of OFN and break the vacuum with it.
    repeat for a few times an your system will be as dry as the desert.

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    Re: Evacuation in Australia

    what is the surrounding temperature?

    I've made a nifty app (android only) for finding the water vapor point
    https://play.google.com/store/apps/d...surecalculator
    You have to allow for 3rd party installations on your phone as I haven't uploaded it to google yet.

    at 30C, water will boil at 31800 micron, so if there was any moisture in the system, the pressure would stagnate at that point until all moisture has been removed.

    the only way to get below that water vapor point is if you connected a huge vacuum pump that managed to take the pressure down so fast as to make the moisture freeze, in which case you would have to vacuum for ages as you wait for the ice to sublimate into gas form

    Any moisture left in the system is most likely absorbed in oil or oil residue, and that is why you are seeing the changes in pressure, as the temperature rises the oil will give off more moisture.

    First step is to remove as much oil and oil residue as you can, next is to do what chemi-cool said, to break the vacuum with OFN.

    OFN is a dry gas, and moisture will attach to it, so when you purge the OFN it will also draw with it moisture
    Last edited by Tycho; 11-12-2017 at 10:06 PM.
    -Cheers-

    Tycho

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    Re: Evacuation in Australia

    uploaded the app to google store (free) to make it easier for everyone

    https://play.google.com/store/apps/d...surecalculator
    -Cheers-

    Tycho

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    Re: Evacuation in Australia

    Thank you for the advice gents. I do not buy into the nitrogen/triple evacuation thing. I agree that the nitrogen may well sweep out any any water vapour that is inside the system but I do not see how it will remove any water that is liquid or mixed with oil. I am a believer that a long deep vacuum will ultimately force most of the water to evaporate, once it is evaporated it will be brought out by the vacuum pump.
    By the way the vacuum at 1400 yesterday was 1400 microns, at the same time today it was 730 microns, I am definitely seeing improvements, i am still getting evaporation/sublimation, if I wasn't the vacuum would be down below 100microns.

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    Re: Evacuation in Australia

    Using nitrogen is what most techs do.
    If there is oil in the compressor an it is POE, you nee to replace it as POE get ruined from the oxygen in the water.

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    Re: Evacuation in Australia

    Hi

    we have replaced the compressor and evacuated it with a dry sump.

    I agree that Nitrogen is what most techs do, but I still remain to be convinced

    i think I need to set up an experiment to see which is better.

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    Re: Evacuation in Australia

    Quote Originally Posted by Allrounder View Post

    I agree that Nitrogen is what most techs do, but I still remain to be convinced

    i think I need to set up an experiment to see which is better.
    Or you believe all of the physics that have been tested and proved over the years.
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    Re: Evacuation in Australia

    Quote Originally Posted by Allrounder View Post
    I agree that Nitrogen is what most techs do, but I still remain to be convinced
    I had the pleasure of going to Edwards vacuum school for several days.
    A nitrogen sweep is very effective and the reasoning was explained.
    This is settled science.

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    Re: Evacuation in Australia

    Quote Originally Posted by Allrounder View Post
    Hi

    we have replaced the compressor and evacuated it with a dry sump.

    I agree that Nitrogen is what most techs do, but I still remain to be convinced

    i think I need to set up an experiment to see which is better.

    Triple evacuation is a tried and true method that has been used in the refrigeration industry since before all of us here were born. back before two stage vacuum pumps were available, triple evacuation was the only way to dry out a system and achieve "deep vacuum"

    How to perform a triple evacuation:
    -Run the vacuum pump until the pressure stagnates, or around 1500 microns.
    -Disconnect the pump, pressurize the system with OFN to 1 bar (15 psig) (leave the pressure for 30 min as this gives the dry OFN time to moisture)
    -(Another way is to flush the system from one end to the other, but this might take more OFN and still leave moisture in system)
    -After 30 min (or more) purge the OFN from the system.
    -Reconnect vacuum pump
    -Rinse and repeat as needed.


    On larger systems, triple evacuation is the way to go if you want to save time.

    But what is the logic of breaking the vacuum, why not just leave the pump running?

    To understand the logic behind triple evacuation, we have to understand a few things.

    What is pressure?
    air molecules constantly bounce off each other and everything else around them. The force exerted by these molecules is called pressure. Where air molecules are packed closely, air pressure is high. Where air molecules spread out, air pressure is low.
    What is microns?
    Micron is a unit of measurement starting from a perfect vacuum (no
    pressure) that is expressed in linear increments.
    No pressure = no molecules
    So how are microns measured?
    Micron gauges are equipped with a thermocouple on the plant side. This thermocouple is cooled down by molecules bouncing of it, by giving of heat to the molecules, the more molecules that bounces of the thermocouple the higher the micron reading
    So to recap, pressure is the amount of molecules trying to occupy the same space, more molecules means higher pressure.

    What the vacuum pump is doing is not actually lowering the pressure. it is removing molecules, thereby creating a void that other molecules flow towards to occupy, because molecules love to have space to bounce around.

    Above 300-500 microns there will be a laminar flow of molecules moving towards the empty space left by the vacuum pump.

    As we start to move below 300-500 microns the flow will start going from laminar to molecular, meaning that the remaining molecules are now starting to have so much space to bounce around in that they no longer want to go to the empty space created by the vacuum pump, meaning that they happily bounce around until they by pure chance happen to hit the opening where the vacuum pump is connected.

    Now, on larger systems, by doing a triple evacuation with OFN, these pesky air molecules that are bouncing around like a ball in a tetris game, attach themselves to the OFN and when the OFN is purged from the system, they are so happy to tag along to the outside to find a place where they can really bounce around

    Don't ask me to explain the difference between OFN molecules and air molecules, but apparently they move differently

    Again, the triple evacuation is more efficient on larger systems or systems with long pipe runs.

    On a side note...

    The use of the gas ballast valve, unrelated, but there is so many people around that doesn't know what this is for... I've even had one guy turn the gas ballast valve on and off and then say "but the pump sounds the same, so what's the difference?"

    So... a vacuum pump can only remove water/moisture from a refrigeration plant in the form of vapor.
    When moisture enters the vacuum pump, it is in equilibrium with it's surroundings (pressure/temp at the pump inlet). When the gas ballast valve is open it allows a small amount of air in from the surroundings (atmosphere) into the pump before the final compression and exhaust step of the pump.
    This keeps the vapour/moisture in equilibrium and prevents it from condensing and to exit the vacuum pump still i vapour form, preventing it from entering the oil in the vacuum pump.
    (ballast means equilibrium or stability)

    The gas ballast should only be kept open when you have a moisture laden system, as all it really does is keep moisture out of the oil in the vacuum pump.

    A downside with having the gas ballast open is that it will have more "oil throw out" in the form of oil mist so during this initial stage it is advisable to have an exhaust hose leading to fresh air, unless you want to be called back because the fire alarm went of in the middle of the night, or having a panicking client calling to say that the whole room is filled with smoke/fog (and of course the oil film that sticks to everything)

    I use an ITE (like this one http://www.ite-tools.com/en/category...us-accessories) with the oil mist filter, the oil mist filter catches some but not all, so connect a hose to the exhaust leading to fresh air, unless you want to be called back in the middle of the night because the fire alarm went off, or the customer is freaking out because the whole room is filled with grey fog.

    Suction hose should be as large and as short as possible.

    On the outlet of the oil mist filter I have 3 meters (10 feet) with 3/4" clear plastic hose that I arrange as as a U, on the bottom of the U I have punched a 6mm hole (1/4") and below the hole I leave a container/small plastic box that will collect most of the condensate that is pulled from the system, this way I can monitor what is removed from the system and know when it's time to close the gas ballast to start pulling a deep vacuum.

    from the outlet of the 3/4" exhaust hose I run a 1/2" hose to fresh air, because I have been called out in the middle of the night by panicking ship engineers screaming that "your vacuum pump is burning up" because the engine room fire alarm went off and the entire room has been filled with grey/white smoke, and then there is the matter of having everything... and I mean eeeeeverything covered by a thin layer of oil....

    Some people opt for an easier solution, because the vacuum pump is "heavy" and you have already run 30 meter (100 feet) 3/8" steel armored hose all the way from the engine room to the top deck, or the mast, so why carry the heavy vacuum pump all the way down 4 decks?

    Must be easier to just connect it to the 30 meters ( 100 feet) of hose that is already there, right, because then you can leave the vacuum pump up in fresh air and don't have to bother with the exhaust hose...

    And then we are right back to what a vacuum pump really does removing molecules to create a void, and for those last remaining molecules that are happily dancing around, how long would it take for them to dance their way through 30 meters (100 feet) of a 3/8" hose
    -Cheers-

    Tycho

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    Re: Evacuation in Australia

    On another note...

    When measuring the vacuum.

    many technicians connect the micron gauge to the same hose as the vacuum pump through a service manifold or with a T connection with an isolating valve...

    This will never give the correct result when measuring microns. (unless you leave it for a few hours and let the bouncing molecules spread through the system)

    The micron gauge should be connected to the system as far away from the vacuum pump as possible, because the micron gauge is measuring the amount of molecules still bouncing around in the system, close to the vacuum pump, there might be a void of molecules, but if you have long pipe lines, there might be tons of air molecules happily bouncing around further away from the vacuum pump

    In my humble beginnings I were taught that you should never connect 2 vacuum pumps to the same system, the reason being that one pump might be stronger than the other and you could end up with what was said "2 pumps fighting each other"

    But with modern day 2-stage vacuum pumps, this is not really an issue, if it becomes an issue it is because one pump is broken and needs service.

    on Liquid overfeed systems, you can save time vacuuming if you connect one pump on the LP receiver and another one on the consumer farthest away from the LP receiver.
    -Cheers-

    Tycho

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