vacuum timeline

[phicks1065]

My name is Paul, I have been in the Coast Guard 25 years and am stationed in Kodiak Alaska. I have a 33 ton Carrier onboard my ship. The system had a leak on the TXV, we took care of that and stuck the system on a vacuum after evacuation. We have brass caps that cover valve stems. All of our valves leak as we discovered this morning. We came in and found out that our system had not pulled down at all, it was still at 5000 microns. We put balloons on the valves and watched in horror as the balloons collapsed. So, we have been pulling 22 degree air and moisture in all night long. How long should I expect the vacuum pump to take to pull it down to 50 microns?

[The Viking]

Hard to give you a time for it, the best I can do is to give you some pointers on how to do it quicker.

1. Flush the system with OFN (dry Oxygen Free Nitrogen), in through one port out through another, as far apart as possible.

2. Remove all restrictions between vacuum pump and system (Don't use a manifold, use copper pipe and remove any shraeder inserts)

3. Tripple vacc it (pull down to a half decent vacc, flush with OFN. Repeat. Then pull down to a deep vacc)

But, it will only work on a sealed system.



GMY...

PS. If the system is working on modern refrigerant (or uses synthetic oil with old refrigerant) it's worth changing the oil as well.

[nike123]

My name is Paul, I have been in the Coast Guard 25 years and am stationed in Kodiak Alaska. I have a 33 ton Carrier onboard my ship. The system had a leak on the TXV, we took care of that and stuck the system on a vacuum after evacuation. We have brass caps that cover valve stems. All of our valves leak as we discovered this morning. We came in and found out that our system had not pulled down at all, it was still at 5000 microns. We put balloons on the valves and watched in horror as the balloons collapsed. So, we have been pulling 22 degree air and moisture in all night long. How long should I expect the vacuum pump to take to pull it down to 50 microns?

Before you start vacuuming, change vacuum pump oil and check pump performance. During vacuuming, you should change that oil at least once for your case. More then once is recommended.
You will never vacuum it down to 50 microns! For that unit size 600 microns is excellent result and 1000 microns is still very good.
Vacuum it until vacuum reach 400-500 microns. Then isolate pump and watch gauge. If vacuum fall (number of microns rise) to 1000 microns and continue to fall after that value you have leak in system or connections to vacuum gauge. If stays about 1000 microns (in fact, at partial pressure of water at given conditions) you have moisture in system and you should continue with evacuation. If vacuum fall to cca 500-600 microns and stays constant, you should consider your system evacuated.
Time of vacuuming depends on moisture content, temperature, quality of vacuum pump oil, size (capacity of pump), size of connections , system size (volume), length of hoses, etc....
Sometimes, good practice is, to connect old style (Bourdon) vacuum gauge at a beginning of evacuation in order to monitor rise of vacuum until electronic gauge shows clearly, and to find bigger leaks if they are present by isolating vacuum pump occasionally .

I wish you a good vacuuming!;)

[TOTTIHS]

600 micron is not excellent
I presume your unit is inside if possible try & get some heat around it & install a new drier, if its outside & your in Alaska :eek: good luck, as to how long will it take ( a usual customer question) until its done & I don't mean to be rude. If you have a good vac pump & you can get heat around it it won't take too long
Best of luck

[phicks1065]

Right now the micron guage reads 100 microns, when I shut the pump down the reading goes up to 250, but holds steady ( 30 minutes is the longest I have watched it).

[nike123]

Right now the micron guage reads 100 microns, when I shut the pump down the reading goes up to 250, but holds steady ( 30 minutes is the longest I have watched it).
My advice is, consider that as OK! Don't waste time any more.

[wambat]

Sounds good , I would break he vacuum with with dry nitrogen, replace the liquid line drier, pressurize to 150#. let it set for 1 hour if still holding within 1%, blow pressure to 0# gauge pull a 12-15" vacuum and charge liquid in liquid line untill pressures equilize then top off on gas side

[nike123]

600 micron is not excellent


Do you have some other guidelines?
This is from CPS:
2000 microns lowest average industrial requirements for A/C systems
1000 microns medium average industrial requirements for A/C systems
600 microns highest average industrial requirements for A/C systems
400 microns lowest average industrial requirements for refrigeration systems
200 microns medium average industrial requirements for refrigeration systems
100 microns highest average industrial requirements for refrigeration systems
25 microns deep vakuum for special requirements and for testing of vacuum pump efficiency

If CPS misleading me, then I misleading others.

[taz24]

Vac-ing the system and finding all the valve stems to be leaking!!

It is possible for a valve to leak when in a vac and not when under pressure.
With a positive pressure the seal expands a bit and forms a seal, when on vac it offers less of a seal.

Tighten all stems and recap.
Do you have OFN onboard (oxygen free nytrogen sometimes knownas dry nytrogen)?

If you do then follow the Norsemans guidlines and you will not go far wrong.

You need to pressure test the system first to prove it is gas tight.

Cheers taz.

[setrad7791]

Pressurize the system with dry nitrogen to 2000kpa... be sure to pressurize system on both high and low sides to ensure no pressure drops through cpr/epr/tx-valves..... leak test every valve stem/schrader core/post valve/flare nut with soapy water (slightly viscous .....gooey mixture) sorry its the only word i could come up with! After you have made sure their are no leaks take a note of the pressures and leave for 12-24 hours. (note make sure you check the gauge lines with soapy water as well!!!) Check pressure.... You may have to allow a slight pressure drop as the nitrogen may read slightly lower depending on the ambient temp ( Which could be bloody cold considering your in ALASKA!!) If pressure are ok i.e no less a than 2-5 psi pressure drop, release nitrogen and begin evacuation for 12 hours.... Repressurize with nitrogen to 450kpa (60psi) and then release/vent, when pressure reaches 5-10 psi SLOWLY remove liquid line drier and replace including suction line drier if fitted??? you should also replace compressor oil if this is possible and fit a new drier to the oil return line (if applicable.. i.e oil seperator fitted) return to vaccum for a further 12-24 hours and their you have it... I totally dry system. Hope that helps

[NH3LVR]

I found this on the JB vacuum pup site.http://www.jbind.com/FAQ_Micron_Gauges.asp
According to them refrigeration oil outgases about 250 Microns.
Following this reasoning, if you get to 100 Microns and shut off the pump, it will soon rise to 250.
I realize that some modern oils could be different.

[nike123]

Pressurize the system with dry nitrogen to 2000kpa... be sure to pressurize system on both high and low sides to ensure no pressure drops through cpr/epr/tx-valves..... leak test every valve stem/schrader core/post valve/flare nut with soapy water (slightly viscous .....gooey mixture) sorry its the only word i could come up with! After you have made sure their are no leaks take a note of the pressures and leave for 12-24 hours. (note make sure you check the gauge lines with soapy water as well!!!) Check pressure.... You may have to allow a slight pressure drop as the nitrogen may read slightly lower depending on the ambient temp ( Which could be bloody cold considering your in ALASKA!!) If pressure are ok i.e no less a than 2-5 psi pressure drop, release nitrogen and begin evacuation for 12 hours.... Repressurize with nitrogen to 450kpa (60psi) and then release/vent, when pressure reaches 5-10 psi SLOWLY remove liquid line drier and replace including suction line drier if fitted??? you should also replace compressor oil if this is possible and fit a new drier to the oil return line (if applicable.. i.e oil seperator fitted) return to vaccum for a further 12-24 hours and their you have it... I totally dry system. Hope that helps

I don't see in your description any use of micron gauge. That means, that all work mentioned is based on guessing what is achieved vacuum in system by previous experience and rule of thumb and not by measuring really achieved vacuum!
I think that is not acceptable practice today, especially now, when measuring tools are readily available.