Mirrored Orange Spray Paint
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So thereby with that knowledge be applied, in order to pull 28 inches of mercury, 4 shop vacs would be needed all on parallel circuit, and 5 would be ideal. It can be done easily but with each shop vac costing around $50 and the chamber costing about $100 to build, it looks like it would cost about $350 - $400 to create this setup. Not bad all things considered, I just don't have that much money kicking around. =(
BFDesigns said:
Shop vacs in parallel would still get you 7" of mercury but would allow you to evacuate a given volume more quickly.
As in an electrical circuit with pressure being analogous to volts and current to air flow, having two voltage sources in parallel doesn't give you 2x voltage (psi/in Hg) but 2x current (CFM). Shop vacs in series gets you a little boost but the improvement is not linear. The design of the pump just will not move air below a certain point. Air leaks back past the pump vanes as fast as it tries to pump it out. Which is one reason high vacuum pumps cost money. They have to be precisely machined for a good seal.
From a common sense standpoint, if 4 $50 shop vacs could do the work of one $3500 pump the generally smart people who buy such expensive things surely would have figured that out by now.
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CPU64 said:
Not in a small chamber like the one I described. We have two $10,000 custom bell jar units (~18" ID x 20" tall) with this same pump built into them at my school and they pull 28 in under 5 seconds. It all has to do with your seal.
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