Vane pumps

Rotary compressors are positive-displacement machines. Figure iO-7 shows a typical vane compressor. The operation is similar to that of a vane pump shown schematically in Figure 10-10 of Volume 1, 2nd Edition (Figure 10-9 in 1st Edition). A number of vanes, typically from 8 to 20, fit into slots in a rotating shaft. The vanes slide into and out of the slots as the shaft rotates and the volume contained between two adjacent vanes and the wall of the compressor cylinder decreases. Vanes can be cloth impregnated with a phenolic resin, bronze, or aluminum. The more vanes the compressor has, the smaller the pressure differential across the vanes. Thus, high-ratio vane compressors tend to have more vanes than low-ratio compressors. 

Four-Lobe Pump Sliding Vane Pump... 

Swinging Vane Pump Roller Pump Cam-ond-Piston Pump... 

Figure 3-60. Sliding vane pump (single rotor) [17],...

Most pumps that are used in hydraulic applications have a fixed displacement which cannot be changed except by replacing certain components. However, in some, it is possible to vary the size of the pumping chamber and thereby the displacement by means of external controls. Some unbalanced vane pumps and many piston units can be varied from maximum to zero delivery or even to reverse flow without modification to the pump s internal configuration. 

Provided that the system is initially clean and fitted with efficient air filters, metal edge-strainers of 0.005-inch spacing appear to be adequate, although clearances of vane pumps may be below 0.001-inch. It should be remembered that an excessive pressure drop, due to a clogged full-flow fine filter, could do more harm to pumps by cavitation than dirty oil. 

Vacuum capacities and operating ranges, table, 344, 355 Ejectors, 344, 357 Integrated systems, 344 Liquid ring pumps, 344 Rotary lobe blowers, 344 Rotary piston pumps, 344 Rotary vane pumps, 344 Vacuum equipment, 343 Applications diagram, 352 ASME Code, 344 Pumps, 382 Steam jets, 357 Vacuum flow,... 

The rotor of the vane pump is mounted off centre in a cylindrical casing (Figure 8.9). It carries rectangular vanes in a series of slots arranged at intervals round the curved surface of the rotor. The vanes are thrown outwards by centrifugal action and the fluid is carried in the spaces bounded by adjacent vanes, the rotor, and the casing. Most of the wear is on the vanes and these can readily be replaced. 

CVD does not usually require the low pressures which are necessary with sputtering, MBE, and other PVD processes. Consequently the vacuum system is simpler and less costly. Mechanical pumps are adequate for many operations. Vane pumps, built with corrosion resistant material, are preferred. If properly maintained, these pumps will operate for long periods of time. 

The central transport chamber is an 80-cm-diameter stainless steel vessel, and is pumped by a 1000-1/s turbomolecular pump, which is backed by a small (501/s) turbomolecular pump to increase the compression ratio for hydrogen, and by a 16-m /h rotating-vane pump. UHV is obtained after a bake-out at temperatures above 100°C (measured with thermocouples at the outside surface) of the whole system for about a week. A pressure in the low 10 " -mbar range is then obtained. With a residual gas analyzer (quadrupole mass spectrometer, QMS) the partial pressures of various gases can be measured. During use of the system, the pressure in the central chamber is in the low 10 -mbar range due to loading of samples. Water vapor then is the most abundant species in the chamber. 

The speed of rotary vane pumps is nearly constant from 1 atm down to 10 - torr (see Fig. 1.7). To obtain higher speeds in the 10 2—10-3 torr range, booster pumps are used in series with rotary vane pumps. 

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

A system of cascaded booster pumps has the characteristics of a medium-size rotary vane pump but does not present the drawback of the back-streaming. For this reason, it finds application in cryogenics, for example, for the circulation of the He mixture in dilution refrigerators. 

Rotary style valves, 20 685 Rotary tackmeters, 14 316 Rotary tumble dryers, 18 732 Rotary vane pumps, 21 71 Rotating anode X-ray tube, 26 413 Rotating arc reactor, 1 211-213 Rotating biological contactor defined, 3 759t... 

Example The vacuum system of non-benchtop mass spectrometers consists of one to three rotary vane pumps and two or three turbo pumps. Rotary vane pumps are used for the inlet system(s) and as backing pumps for the turbo pumps. One turbo pump is mounted to the ion source housing, another one or two are operated at the analyzer. Thereby, a differentially pumped system is provided where local changes in pressure, e.g., from reagent gas in Cl or collision gas in CID, do not have a noteworthy effect on the whole vacuum chamber. 

Fig. 11.2. Schematic of a thermospray interface. A cartridge heater B copper block brazed to stainless steel capillary C capillary D copper tube E ion lenses E quadrupole mass analyzer G line to rotary vane pump H ion exit aperture J source heater. Reproduced from Ref. [30] by permission. American Chemical Society, 1983.

Important note Particularly in rough vacuum technology, partial pressure in a mix of gas and vapor is often understood to be the sum of the partial pressures for all the non-condensable components present in the mix - in case of the partial ultimate pressure at a rotary vane pump, for example. 

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