A previous thread brings up something that I would love to see
addressed by turners with A/C refrigerant type vacuum pumps anyone that
has experience with them. Our club is in a very spirited debate about
this subject and with a lot of us looking to build vacuum systems, we
are split on this pump type question.

I am in construction, and see the Robinaire, Gast, Yellow Jackets and
on and on used daily by the A/C guys to evacuate the lines before
charging with freon.
By nature, these pumps use replaceable oil that also traps and filters
out the particilates that are in the gases sealed in thesystem. These
pumps are used to evacuate a closed system, and they rarely "mist" oil.

However, I have been warned by my amigos that use these pumps that when
the system leaks (think 5 CFM pump trying to pull 27+ lbs.) it has the
tendency to mist oil. A very leaky system will cause not only for the
pump to be unable to attain proper vacuum and evacuation, but will also
make the pump "mist" or leak more.
Sometimes a "fair amount". This "fair amount" is a whole different
subject.

To further muddy the waters, I was in contact with a professional
vacuum pump rebuilding company in CA and they also told me that these
pumps would be unsuitable because of the misting problem. In fact,
they went so far as to advise me against buying their product! They
thought I should buy a true lab type vacuum with no oil bath (except
for the piston)and are watching to find one for me.

But it seems some are having great success with these AC vacuums. I
have only heard of the misting problem here and there, and I am
wondering if it is because the AC pumps are only actually used here and
there and most know better than to use them. For those using these AC
vacuums, how much mist is there?
I am a full time carpentry contractor, and I am here to tell you only
my planer makes more damn mess than the lathe, so I am wondering if it
is a matter of perspective.

Any thoughts? I can get a good 5 CFM pump with a 2 horse AC 115 volt
motor of many different manufacturers delivered any where from $100 to
a 6 CFM Robinair monster brand new with warranty for $250 or so (that
would also do some veneering!). But they are all oil bath pump for
AC. That also means that the oil needs to be changed every once in a
while.

The good capacity, multi CFM lab type oiless vacuum I need to turn
wormy mesquite is proving quite difficult to find. One of our club
members has made one and his GAST is a 3/4 hp pump pulls just a little
over 6 CFM. Cost? He bought the pump for $200, put a $125 dollar
rebuild kit on it HIMSELF over a period of two days. Cracks, spalts,
worms are no match for this pump on his OneWay. This pump new is $800,
and professionally rebuilt (IF available!) is around $500. Ouch!

But I am looking for something easier than finding a suitable pump,
then rebuilding it properly. I don't know how to rebuild a vacuum and
would rather be turning than learning something I have no interest in.
This pump will be used on my Jet mini, and my Nova 3000, so I don't see
the point in buying a tiny vacuum.

All thoughts and opinions are completely welcome.

Robert

Robert with the AC Pumps you describe you certainly will get an Oil
Mist if you have excessive Leaks in the system.

However you can get Oil Mist Filters, try Google and you will get an
idea of what is required.

I made one out of Plastic Pipe and Steel Wool and it worked fine.

Richard
http://www.laymar-crafts.co.uk

Refrigeration pumps are designed to pump a much better vacuum than most
of the pumps used for vacuum chucks. The oil is part of the rotary seal
of the pump. The oil absorps moisture which creates vapor pressure when
the oil heats up. This VP competes with the ability of the pump to suck
a lower vacuum. Atmospheric pressure at sea level is 14.7 psi, which we
express as 0 psi guage. This 14.7psi is equal to a column of mercury 30
inches tall. We inverse this to say that the lower the pressure the
higher the vacuum. Therefore 0 psi absolute is 30 " of vacuum. 29.9" of
vacuum equals 0.1" of Hg(mercury) pressure. Refrigeration pumps can go
as low as 50 micons of Hg. This low of a pressure is necessary to boil
water at room temperature. This is how the pumps remove liquid water
and other contaminants from Freon systems. Water boils when it's vapor
pressure equals the atmospheric pressure above the surface of the
water.

Bill in WNC mountains

"Bill" wrote in message
oups.com...
Refrigeration pumps are designed to pump a much better vacuum than most
of the pumps used for vacuum chucks. The oil is part of the rotary seal
of the pump. The oil absorps moisture which creates vapor pressure when
the oil heats up. This VP competes with the ability of the pump to suck
a lower vacuum. Atmospheric pressure at sea level is 14.7 psi, which we
express as 0 psi guage. This 14.7psi is equal to a column of mercury 30
inches tall. We inverse this to say that the lower the pressure the
higher the vacuum. Therefore 0 psi absolute is 30 " of vacuum. 29.9" of
vacuum equals 0.1" of Hg(mercury) pressure. Refrigeration pumps can go
as low as 50 micons of Hg. This low of a pressure is necessary to boil
water at room temperature. This is how the pumps remove liquid water
and other contaminants from Freon systems. Water boils when it's vapor
pressure equals the atmospheric pressure above the surface of the
water.

Bill in WNC mountains

Not very knowledgeable about this subject, but did you mean 50 "microns" of
Hg, i.e., 50 millionths of Hg?

Leif

wrote: (clip) A very leaky system will cause not
only for the pump to be unable to attain proper vacuum and evacuation, but
will also make the pump "mist" or leak more.
^^^^^^^^^^^^^^
If you are trying to pull a vacuum on a "very leaky system," then, as you
say, you will be unable to pull a proper vacuum, so misting is not your main
problem. Get rid of the leaks. Any oil mist your pump produces goes out
into the atmosphere, not into the vacuum chuck--so hang a filter jar on your
outlet. It will collect the oil, and quiet the pump considrably. If you
see oil collecting in the jar, you will want to consider whether it is time
to add oil to the pump.

Yes, I meant 50 microns. Go to the attached site for boiling point of
water at vacuum pressures. Fifty microns is 0.00197". A micron is one
millionth of a meter. Fifty microns is a far cry from the three inches
of pressure still left when you pull the =B1 27" most turners talk about
as necessary for a vacuum chuck.

http://www.delanet.com/~pparish/vac-tabl.htm

Bill

A very important thing to remember about vacuum. The speed or volume of
a vacuum pull is inversely proportional to the square of the orifice or
distance. This in English is: if you double the tubing length between
pump and chuck, it will take four times as long to do the same work. If
you half the smallest port in the system, it will take four times as
long. Most refrigeration mechanics change the oil in their pumps every
time they use them. Large systems require changing oil when half done.
Vacuum pump oil is very special. It has very low vapor pressure, so
that it does not compete against the pump also.

Bill

"Bill" wrote in message
ps.com...
Yes, I meant 50 microns. Go to the attached site for boiling point of
water at vacuum pressures. Fifty microns is 0.00197". A micron is one
millionth of a meter. Fifty microns is a far cry from the three inches
of pressure still left when you pull the ± 27" most turners talk about
as necessary for a vacuum chuck.

http://www.delanet.com/~pparish/vac-tabl.htm

Bill
=================
Bill,
AC vacuum pumps in their normal operation on an AC system are working on a
closed system. In a vacuum chuck system, there is usually some leakage, at
least until sanding and finishing operations close most porosity. The people
I've seen using a vacuum chuck have bleeder valves and a vacuum meter to
prevent the vacuum going too high. Too high a vacuum will collapse large
bowls or platters quite easily and smaller pieces depending on design. Since
the possibility of needing a 50 micron pull down are unnessary, and 27-28
inches are plenty to hold most anything, is oil misting going to be a
problem?

Ken Moon
Webberville, TX.

for wood turning applications you want an oil-less pump - piston or vane is
ok, but oilless.


"Bill" wrote in message
oups.com...
A very important thing to remember about vacuum. The speed or volume of
a vacuum pull is inversely proportional to the square of the orifice or
distance. This in English is: if you double the tubing length between
pump and chuck, it will take four times as long to do the same work. If
you half the smallest port in the system, it will take four times as
long. Most refrigeration mechanics change the oil in their pumps every
time they use them. Large systems require changing oil when half done.
Vacuum pump oil is very special. It has very low vapor pressure, so
that it does not compete against the pump also.

Bill

I am in construction, and see the Robinaire, Gast, Yellow Jackets and
on and on used daily by the A/C guys to evacuate the lines before
charging with freon.
By nature, these pumps use replaceable oil that also traps and filters
out the particilates that are in the gases sealed in thesystem. These
pumps are used to evacuate a closed system, and they rarely "mist" oil.

We had about a dozen of these pumps indoors in production. The misting was a
problem. It was easily remedied. Just attach a hose to the exhaust (they
usually use a hollow handle for the exhaust) and put it in an empty 5 gallon
pail with loose fitting lid. Another option is to vent outdoors.

For your application, since you are not contaminating the oil with water or
chemicals, is to just replace the oil when it turns dark amber or twice a
year.

Dan

PS: The dozen little pumps were replaced with automated equipment and these
larger vacuum pumps have mist filters on them. The oil is captured,
refiltered, and reused.

Refrigeration pumps are overkill for vacuum chucks. If you turn wet
wood, some of the moisture will collect in the oil. This is not a
problem as far as the vacuum obtained is concerned, however I would not
store pumps with wet oil for long periods of time. The water will rust
the internal iron parts of the pump.

Bill

They may be overkill, but they are very readily available. An
excellent A/C vacuum can pulls 5 CFM can be bought brand new and
delivered for less than two hundred dollars and have a full warranty.

I would love to have the "correct" vacuum, but availability and cost
are the biggest drawbacks on that. I am still not understanding how
much mist will be coming out of an A/C pump, and as has been pointed
out they surely wouldn't be used long or hard by A/C standards which
may use one of these for 30 minutes or easily more without turning it
off.

I am stunned to think it could blow out enough oil that I could even
think about recycling it from a large bucket. It will run for 5
minutes at a time and pull about 4-5 inches when I finish my once a
week bowl, not more.

So I still don't understand... will the shop (or me) be covered with
oil without an exhaust filter ?

Robert

They may be overkill, but they are very readily available. An
excellent A/C vacuum can pulls 5 CFM can be bought brand new and
delivered for less than two hundred dollars and have a full warranty.

I would love to have the "correct" vacuum, but availability and cost
are the biggest drawbacks on that. I am still not understanding how
much mist will be coming out of an A/C pump, and as has been pointed
out they surely wouldn't be used long or hard by A/C standards which
may use one of these for 30 minutes or easily more without turning it
off.

I am stunned to think it could blow out enough oil that I could even
think about recycling it from a large bucket. It will run for 5
minutes at a time and pull about 4-5 inches when I finish my once a
week bowl, not more.

Robert, The large bucket we use is for two reasons. First, we have them and
the are free. Second, the large volume gives the mist an chance to settle
instead of blowing out. The amount of oil collected is just a few ounces
over the span of months, and that is for on-off use everyday, every hour. I
use one of these in my shop and I don't notice the mist when I use it. But
then I pull 28" and like someone said, they mist more when pulling almost no
vaccuum. That is, when idling. Dan

In article .com,
wrote:

So I still don't understand... will the shop (or me) be covered with
oil without an exhaust filter ?

The dangerous part is that the inside of your lungs may get a very thin
coating of a very small amount of oil - which can kill you surprisingly
well. It's the aspect of a fine oil mist or fog that is dangerous,
AFAIK. In the labs I used to work in, we had filters and also an exhaust
system which pulled the filtered vacuum pump exhaust outside.

For small shop infrequent use, a simple filter and an exhaust hose to
the outside would probably be fine. The fancier sort of filter is costly.

wrote in message
.com on Monday 09 May
2005 04:12 am:

I am stunned to think it could blow out enough oil that I could even
think about recycling it from a large bucket. It will run for 5
minutes at a time and pull about 4-5 inches when I finish my once a
week bowl, not more.

So I still don't understand... will the shop (or me) be covered with
oil without an exhaust filter ?

Robert

Robert,

Just my 2 cents worth but why not direct the exhaust into a coffee can full
of steel wool? That would trap the oil while allowing the air to pass
through. Just run a short piece of flexible hose into the bottom of the can
filled with some 0 at the bottom and some 0000 at the top.Put a V shaped
cut into the bottom couple of inches of the hose to make certain the bottom
of it doesn't get plugged by oil. Just turn the can upside down over a
piece of screen to drain, no need to remove the steel wool.

Hi Ecnerwal

I do know as a fact that in the large automotive assembly plants where
thousands of air driven tools are used all day, people do not get killed
from the oil mist that is present at all times.

Have fun and take care
Leo Van Der Loo

Ecnerwal wrote:



The dangerous part is that the inside of your lungs may get a very thin
coating of a very small amount of oil - which can kill you surprisingly
well. It's the aspect of a fine oil mist or fog that is dangerous,
AFAIK. In the labs I used to work in, we had filters and also an exhaust
system which pulled the filtered vacuum pump exhaust outside.

For small shop infrequent use, a simple filter and an exhaust hose to
the outside would probably be fine. The fancier sort of filter is costly.

if you can afford $200 for an AC pump, you can certainly get a "correct"
pump. I sell them (used) for less than that, and of course there are other
sources. If you want to use an AC pump, that's a choice you can make, but
don't use the cost of a new AC pump vs the cost of a vane pump as the
excuse. Look around for used vane pumps, or used oilless piston pumps.
Also, 30 minutes is not a long time - I've had my vac pump running for over
an hour on some pieces, maybe even 3 or 4 hours because you can use it to
hold the piece while you finish it. So, plan on continuous duty.

bill
www.wbnoble.com



wrote in message
oups.com...
They may be overkill, but they are very readily available. An
excellent A/C vacuum can pulls 5 CFM can be bought brand new and
delivered for less than two hundred dollars and have a full warranty.

I would love to have the "correct" vacuum, but availability and cost
are the biggest drawbacks on that. I am still not understanding how
much mist will be coming out of an A/C pump, and as has been pointed
out they surely wouldn't be used long or hard by A/C standards which
may use one of these for 30 minutes or easily more without turning it
off.

I am stunned to think it could blow out enough oil that I could even
think about recycling it from a large bucket. It will run for 5
minutes at a time and pull about 4-5 inches when I finish my once a
week bowl, not more.

So I still don't understand... will the shop (or me) be covered with
oil without an exhaust filter ?

Robert

"Bill C." wrote in message
...
wrote in message
.com on Monday 09 May
2005 04:12 am:

I am stunned to think it could blow out enough oil that I could even
think about recycling it from a large bucket. It will run for 5
minutes at a time and pull about 4-5 inches when I finish my once a
week bowl, not more.

So I still don't understand... will the shop (or me) be covered with
oil without an exhaust filter ?

Robert

Robert,

Just my 2 cents worth but why not direct the exhaust into a coffee can
full
of steel wool? That would trap the oil while allowing the air to pass
through. Just run a short piece of flexible hose into the bottom of the
can
filled with some 0 at the bottom and some 0000 at the top.Put a V shaped
cut into the bottom couple of inches of the hose to make certain the
bottom
of it doesn't get plugged by oil. Just turn the can upside down over a
piece of screen to drain, no need to remove the steel wool.

I use an old fairly large 2 cylinder refrigeration pump. I have a oil
separator on the outlet (was only about $10) and then run the exhaust from
it into a coffee can filled with a fibre packing material. After about 3 hrs
running time (spread out over months) I couldn't detect any oil in the
separator or in the coffee can. This made me wonder about lubrication on the
top end of the pump so I know bleed a little oil into the pump every couple
of uses.
The duty cycle of these pumps used for vacuum chucking is way lower than
their intended use duty-cycle and should last a long time. I do have a
pre-filter to keep dust and bigger pieces out but I think it would be much
more tolerant of foreign material than a carbon vane pump.

Billh