A trick used to stabilize and increase the apparent power of
compessed air sources:
have a "receving tank", 5-10 gallons, downstream from the air
compressor. The tank accumulates a volume of compressed air.
when a quantity is used, the pressure is supplied from the
receiving tank so that the air compressor does not have to supply
all the volume; i.e., the idea is that a 1 cfm air compressor,
feeding into a 10 cubic foot container, after 10 minutes, will
behave like a 10 cfm air compressor for a short time (about 1
So, do the same thing for vacuum. Let a small vaccum evacuate a
larger tank, then open a valve when casting and, viola, you have
a large vacuum source.
The idea here is that the tank is cheaper than the pump.
A trick from my mining engineering days.
Mark Zirinsky, Denver, Colorado, USA