accepable levels using a Micron gauge

[kengineering]

During evacuation we have implemented the use of digital micron gauges. Currently I am evacuating to 200 microns or better with no more that a 500 micron rise with-in 30 seconds after isolating vacuum pump. Does this sound acceptable?

I had prviously thought I could use it as a sort of leak check but have bee told this is not a reliable test for leaks. Since he did not seem confident in his thoughts on the subject I thought you guys could help sort this out.
Thanks as always, Ken

[Tycho]

Could you please convert the micron thingy to millibar just to please us metric guys

my converter gives me 500 Micron of mercury (only micron unit there is on it)

so...

500 Micron of mercury = 0.6 Millibar

on a vacuum test, we usually take it dowvn to 3 millibar (2250 Micron of mercury), disconnect and shut off the pump and leave it for 12 hours, if it rises above 7 millibar (5250 Micron of mercury) in that time, we pressure test it again and look for leaks.. tiny tiny tiny leaks.

I've never trusted those digital (by digital you mean electronic I guess) gauges, we use clocks that go from 0 - 50 millibar that we have calibrated once a year, without corrections the last four years

[NoNickName]

As manufacturers we vacuum down to 0.05mbar or 37microns
In maintenance we don't accept a vacuum of over 1000microns

[joel]

hi.

i believe its sounds bad.its not good to reach that reading...it should hold...

try two units of gauge. a digital and analog.

observe...

i suggest drain all chilled water n condenser water if u do have in your system.

hope it will help.

[Brian_UK]

Whereabouts is your vacuum gauge in relation to the pump inlet?

If it is close to the pump then you will get a quick rise in pressure shown due to the pressure gradiant through the tubing etc.

[Andy W]

On a new installation I pressure test with nitrogen prior to vaccing down to 1 mbar with my Robinair pump fitted with an Edwards gauge, another consideration is how sound your gauge lines are, I know mine are in need of replacement and this will affect your pressure rise test.

[Paulajayne]

Whilst vaccing down is a method of testing, the majority of what you are testing works under positive pressue so a "Reverse puff test" is only a guide.

Paula

[US Iceman]

..."Reverse puff test"...

Is this anything like our past presidents comments about " I never inhaled"?

[Dan]

The sensitivity of micron or milibar gauges do make them useful as a source of leak discovery. But keep in mind, the flow pressure is only a single atmosphere in potential. While a pressure test can be as high as 20 atmospheres in potential. Also, you can use the higher rate of flow to make pinpointing the leak easier if you are using an ultrasonic detector or bubbles by positive pressure testing. Or a trace of refrigerant to use a standard leak detector. If you find a leak under a vacuum, you will most likely have to pressure test. So my advice is to do a fine pressure test first and use the vacuum to simply evacuate a proven tight system.

[Josip]

Hi, all

The sensitivity of micron or milibar gauges do make them useful as a source of leak discovery. But keep in mind, the flow pressure is only a single atmosphere in potential. While a pressure test can be as high as 20 atmospheres in potential. Also, you can use the higher rate of flow to make pinpointing the leak easier if you are using an ultrasonic detector or bubbles by positive pressure testing. Or a trace of refrigerant to use a standard leak detector. If you find a leak under a vacuum, you will most likely have to pressure test. So my advice is to do a fine pressure test first and use the vacuum to simply evacuate a proven tight system.

Agree with you Dan,
as per my experience, it is useless to make a vacuum test on huge industrial ammonia plant - it is never-ending story (only to remove some water ). Make a good pressure test and evacuate air/nitrogen.

We use vacuum (divide the system (vessels) with closed valves) for easy charging of ammonia to not run compressors without refrigerant.

Best regards, Josip

[US Iceman]

Pressure test for leaks and vacuum for dehydration and removal of non-condensables (air, etc).

[Tycho]

Hi, all



Agree with you Dan,
as per my experience, it is useless to make a vacuum test on huge industrial ammonia plant - it is never-ending story (only to remove some water ). Make a good pressure test and evacuate air/nitrogen.

We use vacuum (divide the system (vessels) with closed valves) for easy charging of ammonia to not run compressors without refrigerant.

Best regards, Josip

A normal commisioning of a large ammonia plant with us is:
*leak seeking at 2-5 barg
*strength test at 1.6 times the safety valve opening pressure
*leak seeking at 2-5 bar

*vakuum down to max 3 millibar (min is collapsing pipes )
*12 hour droptest, if it rises to above 3 millibar, rinse and repeat (skip the strength test tho)

[Frudge it]

Hi Kengineering ,
Having read most of the previous posts , I thought I'd add some interesting data / developments for you , that we are up to here in Aussie.Firstly we have a code of practice , that states that systems must be pulled down to 100 microns & left under a rise test ( or vacum attrition test is the wording in vogue with you guys in the USA...) for 1 hour.Over that hour , if the system is leak tight , there will be NO more than 100 micron change of the initial micron value at the test start.The vacum method of testing for leaks / mositure is I believe greatly under developed as a resource by a lot of fridgies.Heres some other KEY micron values & their meanings...1000 microns - If you cant hold or make 1000 microns you have a positive leak , 500 Microns - Dry System point below which FREE water vapour cant exist in free form : BUT can remain bound in Oil & pocketed liquid refrigerant , 100 microns , Fully Dry System where ALL moisture has boiled off." Rise tests " - 500 Microns - Minimum of 15 Minutes - No greater than 100 Microns Change = Leak Free , and 100 Microns as per described earlier.CPS whom manufacture the digivac gauge , have some very good product material on vacums & interpretations of micron values.Micron based vacum testing is efficent on up to middle of the market commercial sized plant BUT as a previous poster remarked : "is a waste of time for Heavy Industrial Plant ".The processes work i ALL plant cases , its just the economic viability of applying them to the plant level that you are working on.

[jack_lizhaoyang]

Hi all
Vacuum is not a good way of testing leak unless you are 200% sure your gauge,hose,connection are in perfect condition. I have experience vacuum reading quite good the second day system lost all gas. another time working on an ice machine the gauge show there was a leak, with soap water we couldn't find it. As the leak was big we were really fed up we put the whole machine in a big water tank. The funny bubble came out from our dear charging hose!!!

we

[marc5180]

I have been taught at college that 2000 microns is an acceptable level although 200 microns is the norm to work towards.

[Brian_UK]

I have been taught at college that 2000 microns is an acceptable level although 200 microns is the norm to work towards.

Ah, what do professors know

The instructions on mine, if I remember correctly, said that 1000 was OK for air conditioning and at least 500 for refrigeration.

I always go for the lowest possible in the time allowed. If it doesn't reach a decent level then the time gets extended.

[marc5180]

Ok i stand corrected

[Brian_UK]

Oh no, don't be corrected, shoot the other guy first

[Bones74]

I really wouldn't want to see any rise after a good evacuation ever. Check the hoses, gauges, etc.

[Frudge it]

Hi All ,
Have just logged on & checked further posts on this one.Great points on Clearing your gauges before evaluating the system under vac & Bones - Thats a VERY good comment.Thanks.

[Brian_UK]

Remember also that the pressure test that you are performing under a vacuum comes out at 14.7psi, not a lot is it?

[Mik Dundee]

find a good spot for your vac stat and leave it there. pull a 100/200/300micron vac through copper lines make sure all valves and connectionss are tight. the bigger/shorter the lines the better. let it run over night and isolate your pump in the morn check ya stat go for a latte and a custard tart come back to 100micron your all good.

[Peter_1]

f... isolate your pump in the morn check ya stat go for a latte and a custard tart come back to 100micron your all good.

This is almost like Chinese for me.

[Thermatech]

Chaps

Every refrigeration engineer should do evacuation pressure rise test to ensure all moisture is removed from the system.
If you do 1/2 hr pressure rise test with vac pump isolated then if there is any misture left in system the pressure will rise.
If you pull a hard fast vac some water droplets in system can freeze. You can see good vac but still there is water left inside but it is ice.
Carry out 1/2 hr presure rise test & ice melts, expands into vacume & pressure rises. If pressure rise stabalizes then you know that you still have moisture & not a leak.
Brake vac with dry nitrogen to help removal of moisture & vac again.

[750 Valve]

hey frudge it - are you referring to HB40 (code of practice)... there must be a new one as those figures are WAY out to what I understand. I will contact Australian Standards ASAP to get a new one.

Peter, mick dundee is just living up to his name sake.. thats real aussie fridge slang right there!