Several decades ago, the American Vacuum Society created a standard for measuring the pumping speed of diffusion pumps. Unfortunately, the method behind this standard calculates a pumping speed that is about 70% higher than the actual real world pumping speed. Thus, all diffusion pumping speeds that use the AVS standard are overstated by close to a factor of 1.7.
Later, an international standard was created to measure diffusion pumping speed, the ISO (International Standards Organization). This new standard by ISO is much closer to reality, though still about 25% overstated to actual real world pumping speed. The reason behind the variance to the ISO standard is that measurements for this standard are taken in a laboratory with a single gas, like nitrogen, under laboratory environmental conditions. In the real world, the chambers being pumped are usually filled with atmospheric air. Air contains many gases including water vapor, which is challenging for most vacuum pumps to remove quickly. If you have a high incidence of water vapor in your location, the best pump is a cryogenic pump, which uses the condensable nature of the water vapor to its advantage by freezing the molecules onto huge surface areas. Browse our selection of cryogenic vacuum pumps, on our products page.
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