Rotary Vane Pumps: Technical Notes
This Page From: Lesker Vacuum Systems |
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ApplicationsRotary vane pumps are the basic workhorses for the majority of vacuum installations. The vacuum range covered by a two stage vane pump fits many requirements in general vacuum work and in thin film deposition coaters using a low pressure process gas. Vane pumps can exhaust ("rough out") a chamber to base pressures sufficiently low that an operating high-vacuum pump can be opened. And following roughing, they provide adequate forepump pressure to back a transfer-type high-vacuum pump (such as a diffusion or turbomolecular pump). Apply caution, however, when using a rotary vane pump in conjunction with an ion pump. The rotary vane pump's ultimate vacuum is not sufficiently low for starting an ion pump, since an ion pump has a greatly shortened life if started at pressures above 10-3 torr. The vane pump has another characteristic incompatible with many high or ultrahigh vacuum chambers. At high inlet pressure, the oil vapor backstreaming is usually acceptably low. The forward movement of the bulk gas through the inlet tube creates a barrier to backstreaming. As the inlet pressure reaches 1 torr, however, the backstreaming rate starts to climb. By 0.01 torr, the backstreaming rate might be 100 times greater than at 1 torr. The ease with which these conditions arise strongly suggests every vane pump should be equipped with a well-maintained Foreline Trap to stop oil vapor. Pumps listed for chemical, corrosive, or plasma conditions are constructed from more resistant materials than the normal non-corrosive gas pumps. The pumps still operate with hydrocarbon oils but we certainly do not recommend such oils in corrosive or potentially explosive conditions. In those cases, prepare the pump for an inert Fluid and fill it with one of suitable viscosity. |
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