Medium vacuum range

The transitional range between viscous flow and molecular flow is known as Knudsen flow. It is prevalent in the medium vacuum range = d. 

Classical physics teaches and provides experimental confirmation that the thermal conductivity of a static gas is independent of the pressure at higher pressures (particle number density), p > 1 mbar. At lower pressures, p < 1 mbar, however, the thermal conductivity is pressure-dependent (approximately proportional 1 / iU). It decreases in the medium vacuum range starting from approx. 1 mbar proportionally to the pressure and reaches a value of zero in the high vacuum range. This pressure dependence is utilized in the thermal conductivity vacuum gauge and enables precise measurement (dependent on the type of gas) of pressures in the medium vacuum range. 

N cuum technology acceptance specifications for rotary piston vacuum pumps Part 1 - Rotary piston and vane type rotary vacuum pumps in rough and medium vacuum range Part 2 - Roots vacuum pumps in medium vacuum range ... 

VACUUM PUMPS (ROUGH-MEDIUM VACUUM RANGE) 3.2.1 Oil-sealed Rotary Pumps... 

There are small internal clearances (< 1mm usually) between the rotors and the housing and between the rotors themselves. Relatively low pressures (in the medium vacuum range) can, however, be achieved. Importantly, there is no oil sealing in the gas-handling part of the pumps. The nominal (theoretical) pumping speed (iSth) of a Roots pump is ... 

Roots efficiencies of about 70% or more can be achieved if k0 > 20 and Sth/Sback < io. Although such values for the staging ratio are satisfactory in the medium vacuum range, lower values are desirable if there are large variations in operating pressures or if the Roots pump is working where k0 is small. 

Purity Better (no gas inclusions, very high vacuum) Possibility of incorporating impurities (low-medium-vacuum range)... 

The areas of application for these vacuum pumps are all within the rough and medium vacuum range, the principal vacuum range for chemistry processes. Only the short path and molecular distillation processes rely also high-vacuum pumps like the diffusion pump or even the turbomolecular pump (kinetic gas pumps). High-vacuum pumps are not covered in this book. For these refer to [2, 3]. 

The pumping speed S of a vacuum pump operating in the rough and medium vacuum range is commonly stated in m h . ... 

Leak Detection of Systems in the Medium-Vacuum Range 177... 

Booster pump (vacuum technology) A pump used between the high vacuum pump (particularly the diffusion pump) and the backing pump in order to increase the throughput in the medium vacuum range and decrease the volumetric flow through the backing pump. Example Diffusion pump (DP) exhausts into a Roots blower (booster pump) then into an oil-sealed mechanical pump. See also Vacuum pump. 

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