Casting, altitude ,& Vacum Pumps

Hello Dan in Indianapolis your absolutely right about small vac
pumps being available for under $500.00 However, it is important
to be careful which one you pick and for what application. This
depends on the following. On a Belljar used for investing. the
small bell jars 1/2cubic foot will work with a small pump …but
you need a much bigger pump to evacuate the larger bell jars.
Onone machine that i have , the jar is 25" in dia and 30 " high
and needs to get to 29.9" in 10-15 seconds… we use a 28cfm
Busch pump ($3800.00). we have the ability on this machine to
invest 8 flasks x4"diax8"tall, but usually only invest 6 flasks
in the 4x7 range due to the weight of the investment. We also
have a small swest investing system… this has a 3 cfm cenco
pump. For investing it is important to realize that these pumps
will see water enter the pump through evaporation while under
vac and will recondense in your oil in the pump causing the pumps
to loose vacuum unless the oil is changed regularly. This is
something that many people with small pumps don’t know…
Refrigeration pumps are excellent , but i don’t think that they
handle liquids very well (i’m no expert on refrigeration pumps).
they may make great Casting pumps for cheap money…ie take them
out of an old refrigerator !!! As far as gauges go, anything
above 28+ will work anything above 29+ will work better !!!
(for everyone else… vac gauges do go faulty…i’ve replaced 2
on my small machine). Thats why i have a 450hp chevy motor in my
xjs jaguar…need more power !!! you can never have too much…LOL
wish i could be in Indianapolis for the races. Best wishes Daniel

 I know that vacum pumps capable of pulling deep vacums are
available for under $500.  I regularly pull refrigeration and
A/C systems down to 1000 microns (0.1 inch vac 3D 2,540

PMJI. If the reason vacuum works is that it allows atmospheric
pressure to force the material into the mold, I don’t think
there’s any practical difference between 1000 microns and 10

Using vacuum for degassing might be a different story, although
even there I expect the time in vacuum is more important than the


Dear Dan, Don, and all interested Vacuum- people; Would anyone be
interested in a way of producing 28" of mercury Vacuum in about
40 seconds, with No moving parts or mechanical devices ? I know
of a way, but I’d love to get some input from “vacuum
enthusiasts” about the feasibility of using this Idea. I’m just
afraid that everybody has had enough “input” and that I’ll just
be wasting valuable space here on Orchid. Eben Lenz

Hi Eben, I’m always interested in hearring about how to Draw
vaccum in any form and method. Even did it using a venturi on my
sink tap… at this moment, i’m hitting 29"in 15 seconds…but
every idea that you or anyone has would be helpful. Let me know.
Daniel Grandi

If you get a chance , this is a site that i just set up to view
some casting methods and equipment. Don’s site is also very nice
and well worth a visit.

Dear Eben

I for one would be very interested in the method that you
mentioned about a rapid vacuum system. I’m sure that others will
also want to hear of this technique. Thanks.

Ken Shields
Huntsville (Rocket City), Alabama

Dear Eban , and everyone who have taught me more than I can
recite ; One shore fire way to pull a vacuum is with what we call
a compressed air / vacuum injector . You put in compressed air in
one end and it comes out another along with the ambient air which
is drawn in by " Bernoulli’s principal " This item could / can
be found in the Harbor Freight catalog.and at a modest price. Of
course you need compressed air so here we go again for a
compressor . Another time let me tell you of new adventures in
"Pneumatic Logic circuits" just joking !!! Although I may have
more time to invest into Jewelry and lapidary depending on the
outcome of a upcoming back surgery scheduled in two weeks . So
Thank You all and everyone for the , insights and
humor which You have shared with me. (1/3 faith healer , 1/3
snake oil salesman , and 1/3 skilled tradesman ) . Robert

Hi, Robert. There is a variation on this which uses water flow.
You attach it to a faucet, and there’s a nipple for the vacuum
hose. Since they’re used in chemical labs for vacuum filters, you
can probably get them at Ward’s or Fishers, or Edmunds.

Another time let me tell you of new adventures in "Pneumatic
Logic circuits" just joking !!!

No joke. Pneumatic logic circuits and continuous control
mechanisms, along with measurement and recording devices, were
used for many years in process control. Still are, for that
matter - they don’t break, and some plant managers are reluctant
to replace them.

Hmmmmmm. I was under the impression that sea level pressure
(28.2 or 28.5 not sure) was the most vacuum you could get. I am
sure I must be wrong…


Interesting point. barometric pressure is used as a reference
for a lot, but it varies! I think absolute pressure remains the
same. Extreme deep vacums are measured in millitorrs (=microns),
and reference zero as absolute. I think you may have put your
finger on a reason why common guages are notoriusly inaccurate. So
I would say the question becomes how much above a vacum you
have. Would pressure casters be going the other way from
atmosphere? and what are the practicallities and economies of

Dan Wellman In Indpls

Hmmmmmm. I was under the impression that sea level pressure
(28.2 or 28.5 not sure) was the most vacuum you could get. I am
sure I must be wrong.. JB...

What’s a vacuum? (Revisited)

G’day; it’s nothing. But that isn’t helpful, so lets start

G’day; Take a piece of thick walled glass tube at least a
metre long. Seal one end completely. Fill the tube completely
with mercury. Put your thumb over the end and invert it into a
vessel of mercury. After removing your thumb, the mercury column
in the tube will fall to a certain height; measure the height
(inches, centimetres,- anything you like) of that column from the
surface of the pool and that is the present barometric pressure.
What’s that? There is a mountain of air (atmosphere) above and
all around us, which like you and me, has mass because gravity is
acting upon it (and us). So it is exerting a pressure, just as
we exert a pressure on the floor… So we can now measure the air
pressure acting on the surface of the mercury pool and express it
in inches and it will be whatever the barometric pressure happens
to be today. In cyclone conditions it can fall to 28 inches; in
anticyclonic conditions it can rise to 31 inches. The average is
around 30 inches. So can see that the higher up a mountain you
go, the lower is the air pressure around you. You’re not asleep
at the back, you lot? No? well, let’s get on.

Now, instead of a sealed tube dipping into mercury, suppose you
get another similar, unsealed tube and put that in the mercury
pool too. Now attach your vacuum pump to the end that is open.
When your pump has drawn out as much of the air as it is capable
of, your second mercury column has risen a height of 29 inches.
Today the atmosphere is calm, and the barometer (the sealed tube)
reads, say, 30 inches. So, you don’t have a perfect vacuum.
Unlike the space at the top of the sealed tube. (If you want to
argue that it isn’t really a perfect vacuum, but holds mercury
vapour, come and see me after class. especially if you’re female
and good looking) I could go on, but I see eyes drooping all
over the place so I will leave it at that, and besides, I’ll only
cause worse confusion. Things can get quite complicated;
scientists would tell you that you have a vacuum of one inch or
25.4mm. (see what I mean?) So, ENOUGH! Cheers, and drive

       / /
      / /
     / /__|\
    (_______)  In sunny temperate Mapua NZ -

Autumn’s here…


30" of mercury is the most vacuum possible, but you can never
quite get there. You can get quite close though. A good two
stage oil sealed pump can draw 29.9996 inches of mercury or
better under laboratory conditions.


James Binnion Metal Arts
4701 San Leandro St #18
Oakland, CA 94601

   Hmmmmmm. I was under the impression that sea level pressure
(28.2 or 28.5 not sure) was the most vacuum you could get. I
am sure I must be wrong.. 

No, you’re not wrong. The most vaccuum you can get is no
pressure at all. Since this is only compared to normal maximum
sea level pressure, which is about 29 inches of mercury (or
whatever. What’s the weatherman say today?), that would be the
reference figure. Just remember that vacuum is not a
"something" you can just add more of. It is, in essence,
“nothing at all”…

Mind boggling stuff…

Peter Rowe