Turbomolecular pumps always run in combination with a forevacuum pump. Depending on the size of the vessel to be evacuated, the turbomolecular pumps and forevacuum pumps may be switched on simultaneously. If the time required to pump the vessel down to about 1 mbar using the forevacuum pump is longer than the run-up time for the turbo pump, then it is advisable to delay switching on the turbomolecular pump. Bypass lines are advisable when using turbomolecular pumps in systems set up for batch (cyclical) operations to save the run-up time for the pump. Opening the high vacuum valve is not dangerous at pressures of about 10‑1 mbar.
Turbomolecular pumps should be protected against objects entering through the inlet port and should only run with a wire-mesh splinter guard. There are different versions available in different mash sizes. In addition, sharp shocks to the pump while running and sudden changes in position are to be avoided.
Venting the pump to atmospheric pressure while the rotors are turning may be done only when strictly observing the operating instructions. Under certain circumstances it is possible to operate turbomolecular pumps under exceptional conditions. For example, it can be possible to use a turbomolecular pump in magnetic fields, depending on the pump model and mounting situation.
In a radioactive environment, standard turbomolecular pumps can be used without hazard at certain dose rates. If high dose rates are encountered, then certain materials in the pump can be modified to withstand the greater loading. The electronic frequency converters in such cases are to be set up outside the radioactive areas, since the electronics used inside can only tolerate lower dose rates of radiation. The use of motor-driven frequency converters represent another option which can withstand even more. Leybold can offer the user a number of solutions for this challenge.
Turbomolecular pumps and frequency converters are nearly maintenance free. An exchange of ceramic bearings is recommended every 2 years and can be done by our field service or trained and qualified customers.
Maintenance free turbomolecular pumps include those with contact-free, magnetic bearing technology, with 5-axis active magnetic bearing and drive system, which combines reliability and efficient operation.
If it should become necessary to clean the pump’s turbine unit, then this can be done by the field service engineer or inhouse (depending on the pump application and the level of deposits), while observing the procedures described in the operating instructions or service manuals.