Two stage rotary pump

In the case of operations ranging between 760 and 10 3 torr, the two-stage rotary pump is adequate. Ultimate vacuum, using the diffusion pump installation, is better than 10-6 torr. 

Figure 31 Pressure in a chamber of 1000 L as a function of time. 1, Pumping speed of the two-stage rotary pump 100 m Vh with gas ballast 2, pumping speed of the two-stage rotary pump 200 mVh with gas ballast. (Balzers Leybold Deutschland Holding AG, D-63450 Hanau, Germany.)...

Fig. 1.7. Typical pumping speed vs. inlet pressure of a two-stage rotary vane pump.

Instead of rotary pumps, large water jet, steam ejector, or water ring pumps can be used. For batch evacuation, and the production of hydrocarbon-free fore vacuum for sputter-ion pumps, adsorption pumps (see Section 2.1.8.1) are suitable. If the use of oil-sealed rotary vane pumps cannot be avoided, basically two-stage rotary vane pumps should be used. The small amount of oil vapor that backstreams out of the Inlet ports of these pumps can be almost completely removed by a sorption trap (see Section 2.1.4) Inserted In the pumping line. 

For the pumping of large quantities of gas in this pressure region, vapor ejector pumps are by far the most suitable. With mercury vapor ejector pumps, completely oil-free vacua can be produced. As a precaution, the insertion of a cold trap chilled with liquid nitrogen is recommended so that the harmful mercury vapor does not enter the vessel. With the medium vacuum sorption traps described under a), it is possible with two-stage rotary vane pumps to produce almost oil-free vacua down to below 10" mbar. 

However, if the pumping process is such that the maximum throughput of 9.5 mbar i/s is uniikeiy, a smaiier backing pump can, of course, be used. This is seif-expianatory, for exampie, from line b in Fig. 2.76 b, which corresponds to a maximum throughput of only 2 mbar l/s. In this case a 25 m /h two-stage rotary-piunger pump would be sufficient. 

Vacuum is provided by a continuously running two-stage rotary vacuum pump (P). A three-way valve M) connects the bell jar either to the vacuum line or to the pressure line. Inserted into the vacuum line is a valve (N) which has a permanent bypass consisting of a coil of long, narrow steel tubing. In order to prevent the liquid in the cup from boiling, caused by too sudden fall in pressure, the system is evacuated first through the bypass with valve (IV) in the closed position. This valve is opened after a predetermined delay period. 

A vacuum vessel (V = 50 L) is evacuated by a diffusion pump backed with a two-stage rotary vacuum pump. There is a leakage of air into the vessel and a desorption gas load (water vapour) of 1 x 10 4 mbar L s 1. The pumping speeds of the diffusion pump for air and water vapour are 100Ls1 and 120Ls1, respectively. Between the diffusion pump and the vessel is a valve having a conductance for air of 100 Ls"1. 

A two-stage differentially pumped vacuum system consisting of a molecular-beam stage pumped by a rotary pump, and a mass analyser region pumped by a turbomolecular pump. 

The three basic elements of the RAPyD-400 — the vacuum system, the inlet system, and the quadrupole analyzer — can be seen in Figure 3.5. The quadrupole analyzer, which itself consists of two separate parts, lies inside the main vacuum chamber. The high vacuum is attained using a turbomolecular pump, which is backed by a dual-stage rotary pump mounted externally to the main system. The sample inlet system is connected to the ion source of the mass spectrometer via a heated molecular beam tube. Around the underside of the ion source is a copper cold finger, which is cooled by liquid nitrogen and used as a sample dump to prevent carryover from one sample to another. 

For this reason, in large production systems, three-stage vacuum pumps are used. These consist of two-stage rotary vane pumps and a Roots pump. The greatest advantage of such a pump combination lies in the large volume flow rate at low pressures and in the low ultimate total pressure attained (Figure 14.13). 

Figure 2.253 Cross-section of a two-stage rotary vane vacuum pump. 1. Start-up control, 2. exhaust, 3. aeration valve, 4. pump stage 1, 5. high vacuum safety valve, 6. pump stage 2, 7. motor coupling, 8. motor and 9 gas ballast valve. (Pfeiffer Vacuum, 2003).

Vacuum pumps reciprocating piston type decrease the pressure to 1 Torr rotary piston down to 0.001 Torr, two-iobe rotary down to 0.0001 Torr steam jet ejectors, one stage down to 100 Torr, three stage down to 1 Torr, five stage down to 0.05 Torr. 

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