Deep vacuum

[Acrisoft]

Hi

In my last seminar, a student of mine said LG wants a vacuum as deep as 30 microns.

He can only achieve 50 microns, so LG says cannot warranty the equipment

I recomended him to use short hoses and large diameter manifold, but not sure if he will achive it

Is 30 microns vacuum really possible ?

( multiple units split air condiotioning - expansion valve based- no capilar tube)

Moises

[coolstuf]

HI,

Pipework must be evacuated to below 2 Torr or 2.7 mb or 270 Pa or 2000 microns. Below all these pressures you are sure you don't have any moisture left in your pipework (after rize test). The lower the better, but with standard vac pumps I think 30 microns will be hard and use a lot of electricity.(I think LG probably mean below 500 micron)

Hope it helps

[robin r33 gtr]

My cps torr gauge instructions say


Air conditioning

vac to 1000 - 500 microns


refrigeration


vac to 500 - 250 microns

I have seen a few small split units vac down to 25 microns but not very often. I try and vac everything to 250 microns but sometimes let 500 go.

[Brian_UK]

As most vac pumps will only acheive 25 micron in a 'test' situation I think that trying for 30 on site is a waste of time/effort and unobtainable.

[Magoo]

I go along with Brian-UK, in a field situation the vacuum is a good as your vac pump and oil quality.

[DL A/C]

i generally aim for 250 microns but anything under 500 should be safe, it all depends on how good your vac pump is and how long your piperun and hoses are

[exotiic]

Can it even be proven from the manufacturer as to whether such a vacuum was obtained or not? Seems to me a clause so to void their obligations from their rubbish, if that expected vacuum level is true.

[nike123]

He probably confused -30 inches of Hg with 30 microns.
It happen easily with today's youngsters! They are not much weighted with unimportant details.
And -30 in-Hg is most likely number from LG literature.

Taking in consideration gauge inaccuracy, that is achievable in 5 min.

[Brian_UK]

The UK LG website commissioning instructions give a steam table to work to only...

http://mylg.co.uk/data%20for%20site/...missioning.pdf

[mad fridgie]

The UK LG website commissioning instructions give a steam table to work to only...

http://mylg.co.uk/data%20for%20site/...missioning.pdf

Interesting way of doing it, certainly is not 30micron

[Brian_UK]

Interesting way of doing it, certainly is not 30micron

You spotted that also

[nevgee]

30" Hg is absolute vacuum ...isn't it? So there's never any chance of achieving that.

Running a Deep Vaccuum is probably not as quick as triple evacuation.

Essentially the purpose of vacing out is to remove non condensibles and moisture. That alone would be dependent on the ambient temperature of the equipment being evacuated.
In such cases 4 Torr, as deemed adaquate by the C&G 2079 course, would boil water in the system at -6.7 C Probably adequate for most install situations.

Whereas, 2 Torr would be -16.4C

and 1 Torr would be -25.4 C.

Is there any reason to be lower than this unless your evaporator is in a cold room / blastfreezer?

[nevgee]

boiling point calculator

http://www.partyman.se/boiling-point-calculator/

[nike123]

30" Hg is absolute vacuum ...isn't it? So there's never any chance of achieving that.

You are right, but 29.9212598 in-HG is 1000 microns.
Try to spot that on your regular gauges!
Their instalation instructions is to not use electronic vacuum gauge. Instead, they advise to vacuum until on your regular gauge you see absolute vacuum (on some gauges marked as -30 in-Hg) for some period of time.

[Magoo]

Vacuum and vacuum gauges are one thing, add vacuum pump and oil quality, and have a totally confusing situation.
Try standing / holding vacuum tests with what ever you have. This will be a fare indication of system dry ness and tightness.
magoo

[nike123]

If the system holds the vac at the level achieved there is no water vapour
present in the pipe work, however if the pressure raises water vapour boiling in the tubes
will be the cause of this. In this case continue to vac the system for a further 15 minutes
etc.

[dan wong]

Example for discussion purpose only. not something I do. so don't get up in arm.

Say you just replaced a compressor and you installed a new filter/dryer. You vacuum the system to 29.9"-Hg. That mean there is roughly 10,000 micron. shouldn't the dryer remove the rest of the moister (if any)? why do you still need a deep vacuum?

[Brian_UK]

It may remove the miosture but could also end up being full of moisture with no spare capacity.