Hi to all,
I bought a pump (1.5 CFM) for vacuum investment (jeweler). Today
after 5 min of vacuum of a jar with investment and water. Water and
investment boil but oil has a milky look. What should I do? How can I
avoid that? It is there a filter which can be installed to eliminate
absorption of water into oil tank?
Regards
Gabi B
Romania
You can install a filter or trap for the investment but the water
will always get into the vacuum pump oil. When you pull a vacuum
moisture in air is condensed out of the air and ends up in the oil.
For this reason all pump manufactures recommend changing the oil
after every use. In the AC/refrigeration service industry which is
what most of these vacuum pump are designed for, they change the oil
after only a few uses. In the Jewelry industry, people can’t afford
to do that. If you are able to afford the cost of changing the oil,
use only vacuum pump oil, not other kind of oil. Change it as often
as you can afford to. I change my pump oil after about 10 - 12 uses
depending on how bad the oil looks.
John
The Jewelry Equipment Dr.
Here are some tips I was given by the rep for J/B vacum pumps.
The milkiness is water in the oil, drain out the oil ASAP, then put
about 1/4 to 1/2 of the oil charge into the pump, turn it on, open
the oil drain and block the exhaust port with your hand. This should
put more force behind the oil coming out the drain and help to flush
out sediments in the bottem. After you have gotten the sediments
flushed out you can shut off the drain and the pump. Fill the oil up
to proper level and restart the pump leaving it run with the inlet
shut off and the gas ballast open (usually a threaded screw with an
o ring, located by the handle.) Leave run for overnite etc. This
will help to clean out the pump some more and can even relap the
seals in the pump if they are worn. Change the oil again if it
becomes cloudy or white and repeat until the oil stays clear. There
are some ways of avoiding getting the water contamination to begin
with. If you pull your vacum from above the water that will help,
also when done pulling a vacum it is a good practice to shut off the
vacum inlet while leaving the pump run for 15 minutes or more with
the gas ballast open. The gas ballast opens up between the stages
and helps to purge air, moisture etc. from the pump and oil.
In large commerical water chillers where they have had a severe
water contaimination they will use a “cold trap” in the vacum line to
pull out the water before it reaches the vacum pump. A cold trap is a
chamber in the vacum line where they run the vacum around the
outside of an inner chamber which they fill with dry ice etc. The
water collects on the walls of the inner chamber and then they can
remove the inner chamber with the condensed water / ice. For your
purposes you should never need anything like that but you could
possibly use some type of a sediment chamber to collect out the water
as droplets before the pump.
HTH
Dan Wellman
First thing is empty and change out the oil. Milky looking oil is
full of water. Second thing is to change the oil regularly if you
are using the pump on a regular basis, once a month is not too often.
Third start the pump running 1 hr before using it to invest with
either the bell jar in place or a stopper in the vacuum inlet so
that it is not just pumping air through the system to allow the pump
and oil to heat up. If the oil is hot the water vapor is less likely
to condense on its way through the pump so it will pass right through
rather than collecting in the oil. Once you are through investing
allow the pump to run for another hour under vacuum to try to flush
out as much of the water vapor as possible. While this will not
remove all the water it will remove the majority of it. Water in the
pump oil is not only a problem in trying to get a good vacuum but
will destroy the pump if it is not kept at a very low level. On Sep
28, 2007, at 3:48 AM, Balsanu Gabi wrote:
James Binnion
@James_Binnion
James Binnion Metal Arts
360-756-6550
*G’day; A few years after the last war I worked with very high vacuum
systems which involved obtaining pressures of a hundredth of a
millimetre of mercury or less. This involved the use of a costly
two-stage pump, followed by an oil diffusion pump as these sort of
low pressures could not be obtained with mechanical pumps alone. Thus
the presence of any water in the pump oil could not be tolerated, and
we used a liquid air trap which froze out any moisture contained in
incoming gases. These had to be changed often to avoid the trapped
water ‘subliming’ and contaminating the pumps. But the liquid
nitrogen we used to freeze out the water wasn’t always obtainable, so
I had a filter made containing silica gel with cobalt indicator
(cornflower blue when dry, pink when damp) which absorbed most of the
moisture which would have contaminated the pump oil, and proved to be
quite effective if not used too long.
It occurs to me that jewellers using vacuum pumps could use a similar
filter to help avoid oil contamination, which would be easy to
maintain. After each use, the silica gel could be spread on a dinner
plate and heated in the microwave oven to regenerate it. I have also
used a reinforced glass jar containing the silica gel under vacuum,
to place a water contaminated watch into for drying. A watch would be
completely dried out in 15 - 20 minutes as water evaporates very
quickly under low pressures.
Cheers,
johnb in NZ