Re: Refrigerant recovery unit -- vacuum pump?

On Sat, 28 Jan 2006 00:01:46 +0000, dnichols@xxxxxxxxxxx (DoN.
Nichols) wrote:

>According to Rex B <"">:
>>
>> Glenn Ashmore wrote:
>
> [ ... ]
>
>> > If it is in good condition the pump should pull down into the mili-torr
>> > range. My cheapo little RobinAir will easily peg a normal vacuum gauge.
>> > It can't keep up with my Sargent-Welch but then you can't pick up the S-W
>> > and haul it around the shop.
>> >
>>
>> I have a medical vacuum pump.
>> Would it be suitable for A/C system evacuation?
>
> I strongly doubt that. Medical vacuum pumps are used for
>removing fluids pooling in a area of surgery -- kind of like the pump
>put in your mouth at the dentist's. Medium flow, not particularly
>strong vacuum.
>
> Strong vacuum would be likely to damage tissue if the tissue
>gets pulled against the intake.
>
> Of course -- there could be other uses of vacuum in medical
>technology which could require high vacuums -- but I don't know what
>they might be.
>
>> Any idea if medical pumps have to meet a lesser spec in terms of in/Hg?
>
> I strongly suspect so.
>
> The pumps used for A/C service are about the grade of the oil
>wetted pumps used as "fore-pumps" in high vacuum systems. They get the
>pressures down to a level where other technologies can take over --
>turbo pumps, molecular sieve, oil-diffusion, and various others which
>can't even be *started* near atmospheric pressure. And those fore pumps
>need to run for quite a while to get even a fairly small vacuum chamber
>down to the pressure levels where the other technologies start out.
>
> And the oil wetted pumps are really *too* good for something
>like desoldering. For that, I would suggest something like the Gast
>brand rotary graphite vane pumps. The oil wetted should be run for a
>long time after the majority of the air is pumped out -- in part to
>remove gases which have been taken up into the oil during the first part
>of the pumping. As they start, you hear a sound sequence like:
>
> Glurk Glurk glurk Poketta Poketta poketta poketta ... tick tick
>tick "murmur" ....
>
>with the "Glurk"s being large bubbles of air being passed through the
>oil bath, the "poketta"s being much smaller bubbles, the "tick"s even
>smaller bubbles, and the "murmur"s being the continuing motion with
>nothing measurable really being pumped.
>
> The first few moments -- for however long the "Glurk"s continue,
>the exhaust side will carry some oil vapor with it. A lab pump usually
>has a trap on the exhaust to condense that oil and drip it back into the
>main pump. Sometimes, the exhaust is pumped to the outdoors, instead.
>
> Enjoy,
>

I did! That is a wonderful description of what it sounds like and
what's doing. Loved it!

.

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