open drive compressor whats a good vacuum?

[jbomba]

hi guys im working on a large open drive chiller at the moment probably about 25 - 30 years old. The compressor has just been rebuilt and i have remidied 2 leaks in the system. One on the liquid line solenoid and one on the pressure relief valve. The unit has held pressure over 24 hours and im convinced there are no more leaks in the system. At the moment i have the unit on vac, its been on for a day with a large vac pump. My problem is im only reaching a vacuum of 1600 microns. I havnt worked on many open drive compressors but ive been told that it is hard to pull a good vaccum on these compressors due to the shaft seal only being reliable under pressure and not a vacuum. Are there any gurus here that could tell me what sort of micron readings i should be reaching?

[Grizzly]

If it is a large system, then you have to ask yourself what are you trying to acheive?
Logically your leaks have not resulted in any moisture being drawn into the system.
On account of positive pressure within the system.
Did you isolate the rest of the system whilst you have carried out your service of the comp?
Or was this pressure test on the complete system?
You can sometimes break the viscous seal on the shaft seal.
Sometimes when that happens you have to live with the best you can get. Although if that were the case I would expect some rise and fall as you start and stop the vacuum pump.

my answer will depend upon how much of the system you are testing?

Grizzly

[mbc]

Is it NH3 or C L F system
in old system oil goes to system and with oil mixed we refrigerant gas,and in vacuuming time gas comes from mixing oil does not let vacuum comes down and it takes time , So do not worry about that ,
Also in large system we have air vent valves or air purge system special in NH3, after you charge system and system comes to normal you can use those valve to went air for couple times,

[RANGER1]

I would suggest you isolate compressor from system & then evacuate if yo want good vacuum.

Also how good is your vac pump? have you checked it.

What pressure did you pressurize it during test ie needs to be as high as possible without blowing reliefs or damaging equipment .Find component with lowest pressure rating & pressurize to that which would suspect to be relief valve setting minus 10%.

How did you leak test ie what method/s.Big blue is excellent, NOT soapy water.

Final test, does it actually hold vacuum with vac pump off for a period

Its all time, trial & error to achieve best result

[Grizzly]

Hi Ranger.
What's big Blue?
I am assuming it's like one we have over here that I favour called Snoop.
I have used a yellow putty that the navy Electricians use called Mills Putty I think. (It's like Plasticine)
Where I would roll it out into a long sausage shape wrap that around the drive shaft at the point where the shaft disappears into the shaft seal housing.
This was usually enough to satisfy even the most stringent Navy Vac test.

Grizzly

[RANGER1]

Grizzly,
I remember know that you have mentioned that putty before, which is a good tip.

Big blue is an American micro leak detection liquid that can easily find the finest of leaks.
You carefully spray it on pipe joints covering joint completely with film of big blue, fittings etc, if a leak is present it will foam or bubble up straight away.
If you apply it & check it later micro bubbles will show up like fine foam.

Its same as soapy water but a lot more effective.

Not cheap, but you have to look at the big picture ie expensive labour & refrigerant cost.
Usually buy it by the box as its cheaper.

[Grizzly]

Hi Ranger.
Snoop is the same only applied in liquid form rather than aerosol.
Behaves much as you describe and a very good means of confirming a leak.
Also bought in larger quantities to reduce cost.
Grizzly

[RANGER1]

Grizzly, check out link as it explains very well. Probably the same in every way , but may be cheaper than swagelok snoop.
www.refrigtech.com/sitemap.html

look under technical leak detection manual

[Grizzly]

Grizzly, check out link as it explains very well. Probably the same in every way , but may be cheaper than swagelok snoop.
refrigtech.com/Product/Leak_Detectors/Big_Blu/bigblu.html

Ta my friend and I will be raising a glass or 2 over the next few days.
I shall have one for you as we say.
Cheers Grizzly

Yep looks very similar, I have saved the link for future consideration.

[RANGER1]

Thanks Grizzly, all the best

[jbomba]

hi pressure tested system to 300 psi. i am pressurte testing the entire system as it has suffer a leak on the pressure relief valve. i will try to isolate the compresssor on next vacuum and see what happens. Yes my vac pump is good and yes im using big blue

[Grizzly]

hi pressure tested system to 300 psi. i am pressure testing the entire system as it has suffer a leak on the pressure relief valve. i will try to isolate the compressor on next vacuum and see what happens. Yes my vac pump is good and yes I'm using big blue

jbmba.
Thanks for your answer.
So, to recap!
You have proven where you lost your refrigerant from, you have proven your repair.
The leaks where whilst the system was at positive pressure, so no Air / moisture would of been introduced.
The only area you are cautious of is the compressor, which as agreed can be isolated and treated separately.
Within this you have managed to pull 1600 microns so far which should be suffice to removed any contaminates introduced whilst carrying out the rebuild.
What you don't tell us is what refrigerant this system is on?

If it makes you feel better try pulling a deeper vac on the isolated comp. but for a large system "Of Age!"
You have done a pretty good job of it so far.
Why so worried about a deep vac, when your sequence of events so far don't require it?
You seem to have shown due diligence through-out. I would not be trying to beat yourself up about the last few microns.
In my opinion you have pulled the system down far enough to meet system needs and best practice.
Grizzly

[Magoo]

Hi Grizzly.
just about the "big blue "that Ranger mentioned. Excellent product, spray it on and watch, come back and the smallest leak not first obvious, grows a white beard after a period of time. Fairly standard for every serviceman over here to carry a big blue pump spray.

[D.D.KORANNE]

Also check when was the vac pump oil was changed ?????

[jbomba]

good news guys i shut the compressor off and managed to pull a vacuum of 380 microns. im in the process of charging the system at the moment. Seeing this system is so old ive had no luck on getting the base charge from trane. I plan to start with 70kg of r22 and go from there with superheats/pt. Are these chillers designed for a standard superheat setting or does it vary depending on model of chiller?