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The basic science of vacuum clamping involves the atmosphere. Essentially all atmosphere from beneath the workpiece is removed. The atmosphere above and around the workpiece is what actually holds it in place.

At sea level, the atmosphere provides 14.7 psi of holdown force. However, for every 1000 feet of elevation you lose about .49 psi of holdown force.  For example, a workpiece held down by a 12 x 12 square area would effectively have 2116.8 lbs of hold down force at sea level.

Vacuum is measured in inches of mercury (hg). A perfect vacuum is 30 inches of mercury (30 hg) but the maximum we can draw is 29.92Hg at sea level under perfect conditions. See the following table for examples.


Altitude (FT) Atmospheric Pressure (psi) Maximum Vacuum Attainable (in/hg)
0 14.7 29.92
1000 14.16 28.86
2000 13.66 27.82
3000 13.16 26.82
4000 12.68 25.84
5000 12.22 24.89
6000 11.77 23.98
7000 11.33 23.09
8000 10.91 22.22
9000 10.50 21.38
10000 10.10 20.57
11000 9.71 19.79
12000 9.34 19.02
13000 8.97 18.29
14000 8.62 17.57
15000 8.28 16.88
    

 

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Last modified: November 07, 2008