anybody knows about vacuum pumps?

[e9999]

I have been thinking about setting up a vacuum rig to play with, such as sucking fluids out of hard to reach places, bleeding brakes, fixing ACs, having an emergency setup for the inevitable time when I'll drop the phone in water etc.

I imagine there are different pump systems but I have access to an older one that I believe relies on oil to reach higher vacuums. So I wonder what happens in practice to the oil if exposed to other fluids and especially water vapor. Ways around likely problems? Gas ballast enough? Trap? Or is that type just not suitable for typical garage applications? Anybody knows?

 

[too tall]

Try to find an old milker vacuum pump . They generally have a catch bottle so no intermingling of anything sucked up .

 

[e9999]

thanks for the suggestion. Unfortunately not too many cows around here. As in zero. So not likely I'd find one. And I already have a pump lined up that I can use.

The thing though is that at low pressure the water is vapor so you'd need to cool the trap -if that's what you meant by a catch bottle- down to get any condensate there.

It seems like one can somewhat minimize oil contamination with a gas ballast but I don't know how effective that is in practice. I was thinking that that is an issue that HVAC folks deal with it when evacuating systems.

 

[jblueridge]

I teach science in high school. We have a killer vacuum pump. Very old but the same model is produced today with few changes. I had it serviced recently to replace rubber parts and who knows what else: $750 worth.
http://welchvacuum.com/collections/laboratory-vacuum-pumps/products/duoseal-1402

Because kids do and experience nothing in real life anymore I use the pump with a big bell jar and we put all sort of inanimate things in there. We start by boiling water at room temp. Hand sanitizer loses so much heat energy, it's temp will drop below freezing. The pump has to deal with ingesting shaving cream, marshmallow bits and soda pop.
I change the oil right after we finish a round of these sessions.

I was thinking of using it to pull vacuum on my a/c system. Some say these pumps work too well and the water vapor will freeze and thus never leave the a/c lines. The little pumps draw the vacuum much more slowly it seems.

 

[Pin_Head]

Get an oil-less vacuum pump. You don't need high vacuum for your applications. Sucking water vapor and solvents through a rotary vane oiled pump is bad for them. To prevent damage, you need a "cold trap" frozen to -70C. I have two large belt driven Welch pumps running freeze dryers and they have a cold trap and the pump runs 24/7 to prevent damage. We only shut them off to change oil. Gast and Thomas make nice oil less vcuum pumps that will pump down to 100 microns of mercury or less.

Whether water freezes or not under vacuum depends on its rate of evaporation. The faster the evaporation, the colder it gets. This is how freeze drying works. It goes directly from the solid phase (ice) to dry without becoming liquid. Freezing just means that it is drying out faster.