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  1. #1
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    brazed plate leak??


    Hi all, having thought this one to near death I'm hoping some have thoughts on possible leaks in brazed plate heat exchangers. We have a lazer lab that has a 10 ton R-22 Manuerop hermetic that circulates chilled water (approx. 80 gallons) through a loop to other heat exhangers that cool the lazer machines. The chilled water loop and the lazers are totally separated. Yet we found an oily residue floating in the top of chilled water barrel.

    The compressor has failed by a somewhat quick burnout. The oil was drained from the crancase and about a tablespoon of water was found. The liquid line dryer had plugged and when cut open about another tablespoon of water was found. It was an Emerson dryer and therefore not a molded core dryer. The water cooled condenser and the BP evaporator have been isolated and pressure tested for 3 days with no pressure loss whatsoever. The BP evaporator was subjected to a vacuum test with a micron gauge and held to 1000 microns ( we were pressed for time late Friday afternoon).

    The 3 phase grounded compressor burnout can be traced to a faulty contacter but it's the moisture found I'm having the problem with. This compressor was changed out 2 months ago by a fellow that is no longer with us, so he's not around for me to ask questions.

    Oh btw, the CW flow switch failed closed. The manual reset freezestat was not tripped and was set at 40F. It uses a Ranco 1 stage electronic thermostat. The CW pump runs 24/7 and chilled water setpoint is 50F off and 60F on. Pump down control is set at 5psi.


    I suppose I could attribute the moisture to a real sloppy compressor changeout. Or is it possible for a brazed plate evaporater to pop a leak and then close back up?



    thoughts?



  2. #2
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    Re: brazed plate leak??

    B”H
    “The water cooled condenser and the BP evaporator have been isolated and pressure tested for 3 days with no pressure loss whatsoever.”
    At what pressure you tested both items?

  3. #3
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    Re: brazed plate leak??

    I am with Mike.
    The pressure you use is relevant.
    Personally I would take the vacuum much lower 1000 microns seems to high to me.
    (Sorry I cannot be more precise on that only I don't work in Microns.)

    Anyway on a very low vacuum I would at least expect the vacuum gauge to rise and fall as the moisture boiled off. Especially given the amounts of water you have found.


    With a pump-down pressure of 5 psi (-30F/ -34C) I suspect you may well have damaged something.


    You need to use more aggressive pressure to prove your BPHE. is sound.

    By the way What's an Emerson drier look like if it is not solid core?
    Grizzly

  4. #4
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    Re: brazed plate leak??

    I was thinking there was a localized tiny freeze up that closed up during a vacuum test. Those plates are thin and might move slightly. Long shot i know.

  5. #5
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    Re: brazed plate leak??

    u need to perform a pressure test on the fridge circuit to the maximum test pressure,leave a gauge on it and record the ambient air temp, u may see bubbles on the water circuit, leave it on test for 2-3 days, fit a large drier core, also a suction burn out drier, also possibly add spectroline glostick the the fridge circuit,a fridge circuit at 1000 microns is pointless if ur trying to prove the heat exchanger is sound before reinstating. also triple vac it- good luck

  6. #6
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    Re: brazed plate leak??

    if you want to go for very sensitive way for test. pressurize one side and in second side seal one hole and put colorless hose ( narrow hose is better ) with colored water inside that in second hole and mark the level of water on hose .( in U shape )
    any small and tiny leaks push colored water on hose.
    I done this type of testing it is very good ,
    also you have to look for area temperature it should be fixed ,hot and cooled affect to your water level
    Last edited by mbc; 04-12-2011 at 06:47 PM.

  7. #7
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    Re: brazed plate leak??

    The pressure test was 110 psi with nitrogen. The vaccuum test was done towards end of shift on Friday and that's why it only reached 1000 microns. It held steady at 1000 for half an hour. The micron gauge is an analog meter.

    The Emerson 30 cubic inch L L dryer has fiberglass filters and and a small handfull of dessicant beads in it. Much like a Parker dryer. Essentially worthless IMO.

    The 110 psi nitrogen test stood well for 2 days straight and at that pressure it is within operating pressures of the system. The pumpdown to 5 psi should not be a problem as water temps cycle off at 50F. Water side pressure runs at 40 psi. The BPHE is rated to -50C

    While increasing pressure for testing is very valid and I'll probably do that tomorrow, I'm of the mindset that a hole, crack, or any type of breach leaks all the time and at any pressure. Considering an oily residue in the chilled water side and moisture in the refer system, I'll probably change the BPHE regardless.

    On a further note, this lazer lab is in a building where they teach chemistry. The fellow that works on their lazers showed me his collection of patch cords whose outer insulation has been violently attacked by chemicals in the air over time. The plastic ones are undamaged but the siliconized rubber ones are plain ugly. I was told to wash my hands real regularly. I don't know what grade of stainless steel is used on the HE. The water side is an open system.

  8. #8
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    Re: brazed plate leak??

    Oil in the chilled water can only come from the heat exchanger, i had this issue on a large -5c system, held pressure, had to strip and rebuild the heat exchanger, first in alfa laval irelands history to fail, 3 gaskets had popped out of about a 100!

    i'd replace or rebuild the heat exchanger, cheaper than replacing compressors, get heat on the pipe work and purge with nitrogen and repeated vaccing.

    al
    Mostly found in the southern part of this green and pleasant land.

  9. #9
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    Re: brazed plate leak??

    Hi daneel.
    I have killed a few brazed plate HX's in my time. The suffer from stress cracks from cyclic temp changes. So have been using double wall HX's lately. If welding onto stubbs immerse body in water first, I prefer the connections being screw fitting so no welding near the body at all.

  10. #10
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    Re: brazed plate leak??

    B”H

    I would like to bring to your attention that majority of PHE are brazed with copper. If the atmosphere in the air is aggressive and the loop is open I would be cautious about electrochemical corrosion. When the chiller is off be sure that the refrigerant is not "locked" in the BPHE. I would pressure test both BPHE at 300-350psig. Check with the supplier re: the pressure test.

  11. #11
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    Re: brazed plate leak??

    It doesn't sound like it is too big of a HX. Why not just get a new one. All the testing will end up costing more anyway.

  12. #12
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    Re: brazed plate leak??

    Quote Originally Posted by Magoo View Post
    Hi daneel.
    I have killed a few brazed plate HX's in my time. The suffer from stress cracks from cyclic temp changes. So have been using double wall HX's lately. If welding onto stubbs immerse body in water first, I prefer the connections being screw fitting so no welding near the body at all.
    I think that this is a critical point. Using a vented condenser would have protected the system.
    Innovator, IP trader - Rarefied Technologies
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