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Vacumm chamber casting unit

TROUBLE).I am interested in building one.I have a vacuum pump 3 CFM
(85),Will this be enough to pull 29.7 inc…of mercury.What type of
vacuum gauge do I need.Any help you could give will be
appreciated.Dale Harper

Hi Dale,

You would have to call the pump distributor or manufacturer to find
out if the pump is rated for 29.7 Mercury. The CFM displacement has
nothing to do with the vaccuum level the pump can draw. Vacuum gauges
are available from any air cylinder/ component distributor in your
area or from Graingers, McMaster Carr or MSC .

Daniel Grandi casting and finishing for the trade

Hi Dale,

Your vac. pump will work if the area you are trying to vacuum is not
to large. Obviously it would pull enough vacuum on any amount of space
but with investing and casting there are time limits. If your area is
too large you will need a larger vac. pump to create the needed
amount of vacuum in the proper time frame. Another consideration is
that with a more powerful vac. pump you will get better movement
through the investment in the flask during casting.

For Vac. casting you are not looking to get 29.7 in of mercury. If
you attain this you have a problem. You should not get a real high vac
reading when you have the flask under vac. Once you pour the metal the
vac should be higher but still not a full vac. As for what a full
vacuum is: that depends on your altitude. 29 in vac can only be
reached at sea level if you are not at sea level your full vac. will
be different. The reason you should not be able to pull a full vac.
on a flask even after it has been cast is that the investment is
porus. so it should be able to pull air through it even after the
metal is poured. However, you should see very close to a full vacuum
on your guage after you have poured the metal.

The guage you need is a vacuum guage. We have those for $8.37 for a
standard gauge or $36.00 for a liquid filled gauge.

You can reach us toll free at 1-877-262-2196 or email at

If I can be of any more help let me know.

Ken,how about a storage tank for Dale instead of a larger vac.pump
and motor???Of course it would be installed between the pump and his

Ralph Cross
Fremont Jewelers

Hi Ralph, Sorry it took a little while to respond. I just installed
the new version of eudora and it took over my whole computer. Once I
got it calmed down I lost all of the messages in my inbox except 10!
So I had to find your message so I could finally respond. Isn’t
technology great!?

Anyway, a storage tank could work if it was large enough. But again
once the vacuum is used up in the storage tank he will only have a 3
cfm pull. The other thing to keep in mind is that with a storage tank
when you open the valve on it you will have a full vac placed
immediately on the bell jar. For investment this could cause too much
turbulence. So it would be best to slowly open the valve.

Dale was wanting to vac. a urethane pre polymer. It is like
vacuuming RTV for a mold it takes quite awhile even after you have a
full vac. on it. So in this instance a stronger pump would help more
than a storage tank.

Ken Kotoski
MPG Repair