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nike123
03-09-2014, 10:37 PM
Does anyone have any documentation about acceptable leak rate when we do vacuum leak test!
I am unable to find any literature except one precommisioning documentation from my recent job at oil field equipment in Kazahstan.


In that documentation is stated that after isolation of system from vacuum pump when it is 500 microns has achieved and held for specified time, system pressure should not rise more than 100 microns per hour. Monitoring time should be at least 4 hours after 1 hour of initial monitoring (where pressure should not rise at rate more than 100 microns or else evacuation should be continued). And, end vacum after these 5 hours of monitoring should not rise above 1000 microns.

I am unable to connect, let say, 0,5g/y of R22 leak with vacuum gage leak rate in microns per hour.

Here is some literature about that, but I am still unclear how to connect these two numbers.
http://www.vtechonline.com/pdf/VTech%20Leak%20Detection%20Methods.pdf

Question is inspired with this video:

https://www.youtube.com/watch?v=cI6pSBaskjc

hookster
04-09-2014, 07:15 AM
You obviously have some serious thinking on the go nike123? Most of us just think leak oh yes, lets fix it!

There is some excellent information on the institute of refrigeration service engineers section.
For example the evacuation procedures which is free to service engineer members.

http://www.ior.org.uk/ior_filter_technical.php?r=34EM3M4NAE


My attempt is this!
The refrigerant leakage rate can be calculated in flow rate as per below, then you will need to convert your vacuum leakage to a flow (leaving this to you :p ) Qleak= Qrefrigerant x Vrefrigerant / Vleak.

PV=G/MRT

if G= 0.5grams
m=86.47 grams/mole R22
R= Gas Constant 96.15469 J/(kgK)T= 293K

answer in litres per year = 162.9 mbar l/year

nike123
07-09-2014, 09:38 AM
@hokster

Thanks for your input!

It is interesting how nobody else has jet contributed with comments about this topic, and we are suppose to know what we are doing when we do our commissioning jobs.:eek:
I expected lot more inputs about this topic. Or it is very busy week for our top technicians that they have no time for this now?


OFF topic start:
Recently, I don't see many new post here on RE.
OFF topic end.:off topic:;)

Lets continue with subject.:D

In literature leak rate for refrigerant is in g/year. But, I ask myself at what conditions (pressure differential between inside of system and outside of system) are given those numbers? Steady pressure at unit standstill, or condensation highest pressure, or evaporation pressures? I expect at corresponding pressures of at least 50C condensation temperature for given refrigerant (worst case scenario).

Then, how to convert that to vacuum pressure differential (cca 1 bar) conditions for vacuum leak rate test?

Any calculation example?