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Posted by The King on January 14, 2009, 4:56 pm
On Wed, 14 Jan 2009 05:45:42 -0800 (PST), mobrien.acrtc@googlemail.com
wrote:
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>> On Tue, 13 Jan 2009 14:34:42 -0800 (PST), "Marc O'Brien"
>> >With new installations we would ordinarily start the pre-commissioning
>> >tests with a strength pressure test, perhaps for 30 mins, followed by
>> >a 24hr tightness. Then there is a 24hr vacuum finished off with a 30
>> >minute vacuum rise test for moisture.
>> >Is this similar to your procedures?
>> Yup yup except I use a micron gauge to gauge the evacuation time.
>> >Assuming the piping system inadvertently took on say a pint of water
>> >with out you knowing. What would you expect to see on the Torr gauge
>> >after a 24 hr vacuum.
>> Five gallons of used vaccum pump oil and a micron gauge reading of
>> 25000. :)
>> >I have done a few calculations and have recently made a discovery
>> >which I'd like to share but first I ask the above to set a benchmark
>> >against which to discover what is common practice and what might
>> >become new practice.
>> Marc I had a chiller barrel leak and it took me damn near a week to
>> de-hyrdrate the system after I replaced the barrel and it was only a
>> 50 ton machine.
>My next article in the UK industry magazine I write routinely for will
>be on how I insist that the industry's traditional moisture checking
>method be changed. I believe it is flawed. I don't want to give all
>the details right now because I first want to be sure that no one else
>known to me is aware of the flaw I have identified.
I cant wait.
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>In your chiller case above the best process would have been a
>combination of triple vac and deep vac. Triple vac does not remove
>water but does remove vapour contaminants by compounding percentage
>reductions - 4% is left in the system after the first vac and then 4%
>of 4% after the second and finally 4% of 4% of 4% on the third vac and
>so on. Only a deep vac with multiple vac oil changes can remove water.
>The more heat the better and the better your cold trap the less often
>you have to change the oil. But we cleaned a large system up pretty
>quick finishing yesterday after 4 days of alternate deep vac and warm
>nitrogen purging to about 30psi each time. The nitrogen was put into
>the system through a length of copper pipe heated by hand with a blow
>torch. The nitrogen was going in each time at about 40°C. Warm
>nitrogen is an old trick of mine I chose to do on my own as an
>apprentice years back.
>My question everyone is really - at what point after a vacuum do you
>check for moisture and how is it you know you have no moisture - what
>instruments and what time frames do you use. This is for piping on new
>installations.
>> One of my favorite things to do is put a small amount of water in a
>> sealed glass jar and observe the process of moisture removal with an
>> apprentice. Its fun to watch the micron gauge to see at what level
>> things take place.
>> At first the water boils violently then it turns to ice then it
>> sublimes and disappears.
>How much water do you use?
About a table spoon.
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>How long does it take to sublime away?
Its been a while since I've done it but it wasn't long. All the
visible water had sublimed well before 400 microns. I think it was in
the neighborhood of 1400 microns but I may be misremembering. :)
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>I'm assuming this is all done at room temperature and the glass jar is not
>sat on a heat source warmer than the room.
Correct.
Cool video by the way. What was that black stuff in the ice.
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>tests with a strength pressure test, perhaps for 30 mins, followed by
>a 24hr tightness. Then there is a 24hr vacuum finished off with a 30
>minute vacuum rise test for moisture.
>Is this similar to your procedures?