Water vapor tolerance

An important special case in the general considerations made above relating to the topic of vapor tolerance is that of pumping water vapor. According to PNEUROP water vapor tolerance is defined as follows ... 

Water vapor tolerance is the highest pressure at which a vacuum pump, under normal ambient temperatures and pressure conditions (20 °C,... 

According to equation 2.4 an Increase In the gas ballast B would result In an Increased water vapor tolerance In practice, an Increase In B, especially In the case of single-stage gas ballast pumps Is restricted by the fact that the attainable ultimate vacuum for a gas ballast pump operated with the gas ballast valve open becomes worse as the gas ballast B Increases. Similar considerations also apply to the general equation 2.3 for the vapor tolerance p p. ... 

At the beginning of a pump down process, the gas ballast pump should always be operated with the gas ballast valve open. In almost all cases a thin layer of water will be present on the wall of a vessel, which only evaporates gradually. In order to attain low ultimate pressures the gas ballast valve should only be closed after the vapor has been pumped out. LEYBOLD pumps generally offer a water vapor tolerance of between 33 and 66 mbar. Two-stage pumps may offer other levels of water vapor tolerance corresponding to the compression ratio between their stages -provided they have pumping chamber of different sizes. 

Some pumps have easily exchangeable filter cartridges that not only hold back oil mist, but clean the circulating pump oil. Whenever the amount of water vapor present is greater than the water vapor tolerance of the pump, a condenser should always be installed between the vessel and the pump. (For further details, see Section 2.1.5)... 

Pumping of permanent gases with small amounts of water vapor. Here the size of the condenser - gas ballast pump combination is decided on the basis of the pumped-off permanent gas quantity. The condenser function is merely to reduce the water vapor pressure at the inlet port of the gas ballast pump to a value below the water vapor tolerance. 

Section 2.1.5. At a water vapor tolerance of 60 mbar, the lower limit of this... 

It must again be noted that the water vapor tolerance of two-stage gas ballast pumps is frequently lower than that of corresponding single-stage pumps. 

Fig. 3.30 Control of vacuum drying processes by regulation of the intake pressure of the vacuum pump according to the water vapor tolerance...

Regulation of a drying/distillatjon process, taking into account the maximum water vapor tolerance of a vane type rotary pump... 

When aluminized AP composite propellant burns, a high mole fraction of aluminum oxide is produced as a combustion product, which generates visible smoke. If smoke has to be avoided, e. g. for miUtary purposes or a fireworks display, aluminum particles cannot be added as a component of an AP composite propellant In addition, a large amount of white smoke is produced even when non-aluminized AP composite propellants bum. This is because the combustion product HCl acts as a nucleus for moisture in the atmosphere and relatively large-sized water drops are formed as a fog or mist This physical process only occurs when the relative humidity in the atmosphere is above about 60%. If, however, the atmospheric temperature is below 260 K, white smoke is again formed because of the condensation of water vapor with HCl produced as combustion products. If the HCl smoke generated by AP combustion cannot be tolerated, the propellant should be replaced with a double-base propellant or the AP particles should be replaced with another... 

Increased pump temperature. The rugged design of our pumps makes it possible to run them at temperatures of up to 120 °C. Thus the tolerance for pure water vapor, for example, will rise by a factor of five when compared with normal gas ballast operation. 

Adsorbent beds used in the PADRE process have been recycled on a test stand more than 2000 times with no measurable loss of adsorption capacity. Also, the PADRE resin has a relatively high tolerance for water vapor, allowing efficient treatment of airstreams with a relative humidity of greater than 90%. These two advantages make the PADRE process a cost-effective on-site treatment technology when compared to traditional activated carbon systems. 

Therefore, scrubbing is often required. The scrubbing process is not tolerant of water contamination because it can cause the bed to collapse if exposed for prolonged periods to high water vapor pressures or to condensation. Alkaline fuel cells also require the removal of carbon oxides including C02. 

During secondary drying, the product temperature has to be raised to the maximum tolerable temperature of the dried product. This raise can be done as quickly as can be technically achieved in the plant. Raising it more slowly does not make the procedure safer. When there is no more ice in the product, the final temperature can be applied. The only exception may be in the case of very small dry product per vial. Water vapor desorbed at a high rate may take fine particles from the product and transport them to the chamber. The product temperature will approach... 

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