Pumps speeds for

The two independent variables (the axes) show the pump speeds for the two reagents required in the analysis reaction. The initial simplex is represented by the lowest triangle the vertices represent the spectro-photometrie response. The strategy is to move toward a better response by moving away from the worst response. Since the worst response is 0.25, conditions are selected at the vortex, 0.6, and, indeed, improvement is obtained. One can follow the experimental path to the optimum, 0.721. 

For air, nitrogen, carbon dioxide and water vapor, the pumping speed is practically the same. Compared with the pumping speed for air, the pumping speeds of sputter-ion pumps for other gases amount to approximately ... 

Capacity C (mbar I) The capacity of a cryopump for a certain gas is that quantity of gas (py value at T = 293 K) which can be bonded by the cryopanels before the pumping speed for this type of gas G drops to below 50 % of its initial value. 

Table 2.7 Surface-related pumping speeds for some gases...

In contrast to equation 2.33b this equation does not permit a definite solution for S, therefore, the effective pumping speed for a known gas... 

At an intake pressure of p = 1 -10 mbar the pumping speed for the high vacuum pump as stated in the catalog is about 100 l/s, subsequently 50 % of this is 50 l/s. Therefore the pumping speed of the backing pump must amount to at least... 

At an intake pressure of p = 1 10" mbar the pump has already reached its nominal pumping speed of 400 l/s the effective pumping speed is now Sg(f = 200 l/s thus the required pumping speed for the backing pump amounts to... 

If the high vacuum pump is only to be used at intake pressures below 10 mbar, a smaller backing pump will do in the case of the example given this will be a pump offering a pumping speed of 6 m /h. If the continuous intake pressures are even lower, below 10" mbar, for example, the required pumping speed for the backing pump can be calculated from equation 2.41a as ... 

In the case of direct-flow leak detectors, an increase in the sensitivity can be achieved by reducing the pumping speed, for example by installing a throttle between the turbomolecular pump and the cold trap. This is also employed to achieve maximum sensitivity. To take an example ... 

The smallest detectable partial pressure for helium is Pmin He" pumping speed for helium would be... 

Theoretical pumping speed for the roots pump Nominal pumping speed for the roughing pump... 

Neutral species are best sampled using molecular beam methods in which the neutral beam is modulated between the sampling orifice and the ionization chamber of the mass spectrometer and only the modulated component of the mass spectrometer output is recorded. This approach enables all neutral species, including radicals to be detected with a comparable sensitivity. If modulation techniques are not used, the sensitivity for detecting condensible or reactive species is much less than for non-condensible, non-reactive neutral molecules because of the much larger effective pumping speed for the former in the mass spectrometer chamber. However, the ease of installation of non-line-of-sight non-modulated... 

As an example, consider the time required to pump a large air lock with a volume of 50 L from a pressure of 760 to 0.5 torr. The free-air capacity of a widely available pump is 140 L/min, but three-fourths of this is a more reasonable average pumping speed for the above pressure range. Insertion of these numbers into Eq. (3) gives a pump-down time of 3.5 min. This value may somewhat underestimate the pumping time, but the calculation illustrates a method for approximately matching the pump to the patience of the experimentalist. 

Fig. 2.45.1. The diagram shows the pumping speed for a pump set combination consisting of an EH 500 Roots pump and a GV80 dry vacuum pump (BOC Edwards). The advantage of...

Figure 10. Hydrogen and oxygen pumping speeds for the 0.84 Zr, 0.16 Al alloy getter as a function of the oxygen surface loading. Key -X- SHt and -O- So,. (Reproduced, with permission, from Ref. 60. Copyright North-Holland Publishing...

A high vacuum chamber contains a liquid N2-cooled surface (A= 400 cm2) to provide a high, in situ, pumping speed for water molecules desorbing from its surface. Calculate the pumping speed for water vapour at 50 °C if all the impinging molecules are trapped. 

A turbomolecular pump with a DN 63 ISO-K inlet has a pumping speed for N2 of 115 L s 1. It is to be connected directly to a system used for obtaining outgassing data. For this application, the effective pumping speed of the pump is to be reduced to 50 L s"1 by inserting a plate with a circular aperture in the flange. Calculate the diameter of the aperture. 

A gas stream (10 6Pam3 s 1) consisting of 10% H2 in Ar is admitted to a small chamber connected to a triode SIP with a pumping speed for air of 10 L s"1. Estimate the total pressure in the system. 

A portable helium leak detector has a pumping speed for He of 1 L s 1 at its inlet. It is connected directly to a chamber which has its own pumping system. To reduce the test time and also maintain a low enough pressure for the connection of the leak detector, the chamber s pumping system He = lOOLs-1) is used in the test. If the chamber has a leak equivalent to lO mbarLs"1 He, calculate approximately the leak rate (qind) which would be shown on the MSLD. 

When the oxygen partial pressure is raised to a critical value, the process becomes unstable An avalanche effect occurs since the rise in oxygen partial pressure decreases the pumping speed for the reactive gas. The target surface becomes fully oxidized. 

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