Vacuum Pump question.

[matttheniceguy]

What are the chances of someone testing a pair of compressors on a system with a micron guage?

Before wdrzal tried it I would have said low. People who have a micron gauge don't use compressors to vacume a system, and people who use a compressor as a vacume don't own a micron gauge.

Then by trying to remove just a few drops of water fro the bottle on the other side of system.

I'm not too keen on the idea of putting a glass bottle on the high side of the pump, but I was thinking of putting volume marks on the bottle and measuring the rate of evaporation.

As far as figuring out how much of a vacume my pump can pull, I was thinking of trying to boil water at lower temperatures. At 20 degrees the pressure needs to be lowered to 2.339 kPa, which my pump was able to do. At 0.01 degrees the pressure must go down to 0.6113 kPa, or about 4600 microns. If my junkyard compressors can do that, I will be thoroughly impressed.

Here's a question though, why do you need to pull such a deep vacume? I understand the need to evaporate the water from a system and remove most of the gases, but why do you need to pull the vacume so deep? At what pressure/temperature would the compressor oil start to evaporate?

[expansionvalve]

What do you define as low vac?
100micron is a normal figure in my field.
Pulling this sort of vac level gives me peace of mind that all moisture/air in the system has pretty much gone thus reducing the chance that the equipment will breakdown/wear out prematurely, it also helps me sleep at night because if it does breakdown at 3am guess who has to be there by 4am to fix it??
Also, by pulling a deep vac or trying to a micron guage will tell you a little more about the condition of the system, it will indicate the tinyest of leaks and also give you a tiny hint into moisture levels. There have been so many times I have leak tested a system to 300psi and it's held the charge overnight only to find I can't pull a vac due to tiny, tiny leak the next day.
A few effects of moisture and air in systems...
blocked expansion devices or a partial blockage reducing perfromance and wasting electricity, copper plating that ruins compressors, the breakdown of compressor oils... all very important.
I reall am going to sit on my boat here, basically, if you cant pull and maintain a low vac the systems only half good.

[wdrzal]

put the bottle on the high side of a refrigeration loop,while vacuum is connected to the low side.This way you will be pulling vacuum thru the entire system.

Not the high side of the compressor.

by a fast rise in a micron gauge you have a leak.if the pressure rises slowly you still have some moisture in the system.

the reason for such a deep vacuum is that at any pressure above 1 micron there is unwanted gas/air in the system the deeper the vacuum the more that is removed.

A often held misconception is that once you get below 0 psig and read a vacuum there in nothing inside the system, the system is in vacuum, this couldn't be further from the truth, the system is not completly empty until you reach 29.92 "HG of vacuum.

being at 1"hg vacuum just means you are 1" hg below atmospheric pressure not that ther is no pressure present.once you understand the difference between psig(gauge) and psia (absolute)its easy to understand.


you can do your test by boiling the water then put the bottle in a ice bucket, as soon as the boiling stops, note the temperature of the water. We can determine the pressure from this.

[expansionvalve]

That was very well put.

[matttheniceguy]

Well I tried vacuming water at 0 degrees C and it worked. I half filled a bottle with crushed ice and stuck some water in with it to fill the gaps. I connected this to my vacume pump made of two old compressors, and it was able to make the water boil. With room temperature water there are a few very large bubbles, with this ice water there are hundreds of smaller bubbles from everywhere. I guess all the surface area of the ice changes how the bubbles form or something. In any case, I have figured out that my vacume pump can pull at least a 4600 micron vacume.

[shinymod]

nicely done matt

[wdrzal]

yellow jacket came out with a model that reads from .5 microns to atmospheric pressure last year. if some has one of those we could get a accurate reading. all the ones I own only read below 2000 microns . other companys also make micron gauges like tif, supco, robinair.

In any case very good work Matt !!!! now you need to buy a gauge to show just "how Loooow you can go" LOL

While 4600 microns isn't ideal,I think its Super for 2 compressors, I think thats low enough with using a heat gun you can do a very good evacuation on a system.

I wondering if adding a check valve will improve performance even more?

[expansionvalve]

Well done on the mission to proving to some degree a compressor or two will do something worth while
boy compressor technology has changed.

I think that now you have the task of removing moisture contaminated oil from the compressors. now a vac pump has a little sightglass so you can see the oil and a very handy little drain screw on the bottom, so much easier.
Sorry, I whill shut up about vac pumps now

[matttheniceguy]

I'm not sure if I really have to worry about water contaminating the oil. Every time I turn it on it spits out a little oil, so I think I will just have to continually throw a little oil down the low side.

Measuring how much vacume I can pull on my Ghetto vacume pump with a crazy expensive micron gauge just seems wrong. I will stick to ghetto measurements Maby I could try boiling some other fluids at different temps to see what it can do.

[nyTroX]

Water will contaminate the oil. In a vacuum pump application, that is what it's supposed to do. If you see the oil getting milky in a vacuum pump, then you're way past due in changing it. In a low temperature application, you only need a 1/4 of a drop of moisture in your system to clog your cap tubes. Moisture also tends to convert your refrigerant oil to a wax-like substance, also clogging your expansion device, and contributes to increasing your acidity levels in the system from chemical reaction with your hermetic compressor winding insualtion if overheated. Once the acidity level increases, it starts a vicious cycle of increasing further due to more reaction with the compressor windings and further heat due to the failing windings. Eventually the compressor burns out, and you have a very contaminated system on your hands. It's then time for a complete rebuild of your system.
This is a worst case scenario, but not unavoidable. Oversizing your filter-driers will help a bit, and triple-evacuating your systems at least twice may help avoid the bad burnouts. In my opinion, it may be better to invest in an actual vaccuum pump, and have repeated good results in evacuating systems(and save an ass-load of time), than going through troubleshooting a system that may have moisture in it. Hell, if you don't like it, you can always sell it on E-Bay anyways..

Just some toughts from some joker
who does this stuff every day..

[_HL4E_HalfLife_]

I got another used compressor at work today so i added it to my vacuum pump and now with this 3rd compressor i got in series with the other 2. So when i had only the 2 compressors on i couldn't get the water to boil just after it came from the tap because its cool but after i fired up the 3rd compressor the water start boiling right away

[mr-white]

this has been a really interesting read i my self use a compressor to vacuum my system, i only do so as its cheaper and im still fairly new to all this.

would a more powerful compressor work better as a vacuum pump, what would be the minimum for ther job ?

whats the best way to vacuum a system with compressors ?

MW

[_HL4E_HalfLife_]

this has been a really interesting read i my self use a compressor to vacuum my system, i only do so as its cheaper and im still fairly new to all this.

would a more powerful compressor work better as a vacuum pump, what would be the minimum for ther job ?

whats the best way to vacuum a system with compressors ?

MW

The size of the compressor doesn't matter the only difference is the larger the quicker it will pull a vacuum.

MW-"whats the best way to vacuum a system with compressors ?"

set them up just i do in my pic above there in series.

[mr-white]

the reason i asked was because i got told running compressors in series didnt work because the second compressor could only move what the first had removed so it didnt increase performance. then i read it was good to have one compressor on the high side and one on the low both vacuuming together ?

MW