Evacuation, How deep should it be?

[kengineering]

In my quest for a better product I started evacuating down to 500 microns. After isolating the system from the pump the decay seems to settle around 2500 microns. Is there a general parameter or formula of acceptance? Thanks , ken

[Peter_1]

See also this thread
http://www.refrigeration-engineer.com/forums/showthread.php?t=2765
If you can't pump lower than 2500 micron, then everything above 21°C will not change in vapor.
So there's something seriously wrong with your pump (is it anyway a 2 stage?)

[abdulazman]

Ken, try check whether your vacuum analyzer and your vacuum pump functioning properly. Depends on your system tonnage, you ought to vacuum at a longer period of time when required. Try change your vacuum pump oil intermittently during vacuum time until you obtain your objectives. If you still cannot get the microns required. I'm afraid your systems still leaks.

[Dan]

In my quest for a better product I started evacuating down to 500 microns. After isolating the system from the pump the decay seems to settle around 2500 microns. Is there a general parameter or formula of acceptance?

2500 microns is not within the general parameter of acceptance. In refrigeration, it is not uncommon to see a requirment for a vacuum at the farthest point from the pump to maintain 500 microns or less for a period of some hours. We have one customer that requires a 250 micron vacuum with no more than a 500 micron rise within 24 hours. We have to valve off the semi-hermetic compressors because the sightglass o-rings will not let us meet this stringent specification.

[iceman007]

Should be 200 microns. After the pump is isolated, no more than 700 microns. Are you changing the oil in the pump??

[Ahmed_LNG]

i am sorry, but whats the product you are talking about, because iam in the petroleum field, and i dont get it

[iceman007]

refrigeration vaccuum pumps to evacuate all air and moisture from system pipework and components before charging with refrigerant. This must be done as moisture and refrigerants can form harmful acids (eat away the compressor windings etc)

[Ahmed_LNG]

thc ice man, but is this effective ...
in my work .. we use defrosting by hot dry gas then purging with the refrigerant it self.

[iceman007]

It is not just a question of effectiveness, but also of necessity. For example, say an installer installs 50K of refrigeration or a/c equipment and then fails to evacuate it, I doubt any warranties would be valid should the compressor burn out as a result of the engineer's bad practice. Evacuation is something that MUST be done every time the refrigeration system is broken into. Not sure how purging with refrigerant is acceptable. It can't be vented to atmosphere.

[Ahmed_LNG]

iceman , in petroleum companies ... they use the flare system.

[kengineering]

Iceman, You're suggestion of 200 microns and a rise to 700 after isolation sounds about right to me. Would there be a time allotment on the rise. In other words an acceptable rise after 60 seconds? I am in a production shop and time is always a concideration. Thanks for the comeback to all. Ken

[kengineering]

thank you for all your help. After getting set up it was decided to pull down to 90 microns and isolate the system if it holds to a rise below 500 it will pass the test, if not we will have work to do until it passes. Please look at my new question. about txv's. Thanks Ken

[Brian_UK]

Mines supposed to reach 25 as long as it's not connected to anything, with new oil and fresh out of the box, if I remember correctly.

[kengineering]

The systems we build are quite small. Mainly 1/4 HP and 1/3 HP. We use a Ritche 2-stage and work very clean leaving nothing open to atmosphere for more than nessisary. We also use nitrogen during all brazing operations. It seems to be working out OK. If we build larger stuff I guess I'll have to adjust the parameters.