Rotary pumps inlet pressure

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

Of course, the pressure p3 at the inlet of the rotary pump must be less than 0.08 torr, say 0.04 torr. Hence the speed S3 at the inlet of the rotary pump must be at least ... 

In this region the vrater vapor pressure exceeds the admissible partial pressure at the inlet. The gas ballast pump must, therefore, have a condenser inserted at the inlet, which is so rated that the water vapor partial pressure at the inlet port of the rotary pump does not exceed the admissible value. The correct dimensions of the condenser are selected depending on the quantity of water vapor involved. For further details, see... 

Air at 20 °C is evacuated from a chamber using a rotary vane pump (S0 -240 m3 h-1) via a 10 m x DN63 tube. If the pressure at the pump inlet is 6 mbar, calculate pch (pressure in the chamber) and S. ... 

Compute the effect of gas on the pump output. Entrained or dissolved gas reduces the output of a rotary pump, as shown in Table 6.29. The gas in the liquid expands when the inlet pressure of the pump is below atmospheric and the gas occupies part of the pump chamber, reducing the liquid capacity. 

A metal desieeator fitted direetly to the rotary oil pump inlet and provided with a vacuum release valve, a eonnection for a tilting MeLeod gauge and one for the manifold or apparatus, is very convenient if pressures of not less than 10 torr are adequate. 

In theory, the lowest pressure achieved by oil-sealed rotary vane pumps is determined by the outlet pressure which can be discharged either to the atmosphere or the inlet of the next stage of the vane pumps. When the exhaust gas pressure becomes lower than the atmospheric pressure, the gas trapped inside the pump cannot be discharged. If the inlet pressure of 10 2 Torr is produced for the... 

In the first major class of pumps a definite volume of liquid is trapped in a chamber, which is alternately filled from the inlet and emptied at a higher pressure through the discharge. There are two subclasses of positive-displacement pumps. In reciprocating pumps the chamber is a stationary cylinder that contains a piston or plunger in rotary pumps the chamber moves from inlet to discharge and back to the inlet. 

Figure 3.24. Mettler TA 2000 C ihermoanalyzer schematic diagram. I. furnace for regular gas atmosphere 2. furnace for corrosive gas atmospheres 3. inlet valve 4. needle valve 5, gas flow meter 6. pressure gauges 7. exhaust valve 8. shut-off valve 9, bypass valve 10. plate valve 11. fore-vacuum valve 12. diffusion pump 13. rotary pump 14, balance 15. sample cup holder.

Rotary pumps sometimes NPSH is expressed as Net Inlet Pressure Required, NIPR, (or available NIPA), expressed as kPa absolute. 

Fig. 6.11 A schematic drawing of new ion attachment mass spectrometer with the capillary sample inlet and a vacuum envelope with a wall separating ELS chamber fiom mass analyzer chamber. This capillary inlet is fixed on the front flange of the vacuum envelope. 1C ionization chamber, ELS electrostatic lens system, QMS quadrupole mass spectrometer, TMP turbomolecular pump, RP rotary pump. The vacuum envelope is pumped by a single 230 L sec" turbomolecular pump with two ISO-100 inlet flanges (Pfeiffer-Vacuum TMH 261-250-010) plus a 250 mL min" rotary pump. Ionization chamber is closed-type, with a 1 mm < ) aperture through which ionic species are passed. The typical operating conditions are IS pressure with nitrogen gas used as a buffer gas, 40 Pa pressure of ELS chamber, 8x10" Pa, pressure of the QMS chamber, 8 xlO"" Pa. (Reprinted with permission from Ref. [93]. 2012, Springer)...

Optimizing operation conditions, for instance, operate rotary pumps at highest pressures. Cavitation indicates that there is insufficient net positive suction head (NPSH) (NPSH is a measure of the suction head to prevent vaporization of the lowest pressure point in a pump). A good design can eliminate the cavitation in impeller vanes by providing sufficient NPSH and positive pressure at the suction inlet. 

A typical performance range of capacides of rotary lobe vacuum pumps is shown in Figures 6-48A, 6-48B and 6-48C. Another set of curves for rotary lobe pumps, shown in Figure 6-49, provides the brake horsepower, airflow at inlet (CFM) (referred to as their standard volume at 70°F and 29.92 inch Hg abs discharge pressure—essentially atmosphere), and the temperature rise through a non-cooled (no internal or external cooling) vacuum. All data... 

Condensation of vapours must be avoided since it causes a deterioration of the oil water vapour condense at 234 torr at 70°C, which is the typical working temperature of the pump. To avoid condensation, most pumps have a ballast valve in the high-pressure stage. After the gas has been closed off from the inlet, some gas is bled in through the ballast valve. This causes the discharge valve to open sooner, with a reduction of the compression ratio. Rotary piston pumps have similar characteristics. 

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. 

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