Vacuum calculating pumping speed

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 ... 

Equation (1.7) is the general equation for any individual component of the system under molecular flow conditions and with it one can calculate the overall pumping time for a system, if the conductances of the individual components of the system are known. The effective pumping speed at any point along the vacuum line is given by ... 

The following equation can be applied to calculate the pumping speed of a vacuum pump set for a given unit size ... 

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. 

Chapter 2 begins by defining essential terms in vacuum technology - gas flow rate, pumping speed, conductance, etc. It also emphasises a basic assumption for calculation - that continuity is established in a system (what enters must eventually leave). Simple equations are stated and their use demonstrated. 

The walls of a vacuum system have a surface area of 4 m2. The specific outgassing rate ( lh) is 4 x lO PanPs-1 m-2 and a = 1. If it is assumed that there are no other significant gas sources, calculate the pumping speed necessary to achieve lO mbar after 55 min. 

In Chapter 2, essential terms in vacuum technology (e.g. pV-throughput, pumping speed, conductance, etc.) were defined. These are required for the quantification of gas loads in vacuum systems. Calculations based on relevant relationships were demonstrated (Examples... 

The signal response time is important for the safe localization of leaks. It states the time period after spraying helium on the leak until the leak detector indication reaches a defined level (63% of final equilibrium value). Figure 8.3 shows the typical exponential trace of the signal rise. The response time can be calculated from the parameters of the system under test. The critical factors are the volume of the system and the total pumping speed of the installed vacuum pumps. Typical response times of chemical plant systems are in the range of several seconds up to a few minutes. 

Each pump has a specific pumping speed curve, showing the pumping characteristic of the pump as a function of inlet pressure, exhaust pressure, and gas species. Pumping speeds are generally measured and rated either in accordance with the AVS Science and Technology of Materials, Interfaces, and Processes (the old American Vacuum Society) Recommended Practices or the ISO Standards. The gas throughput (Torr-liters/sec) can be calculated from the pump speed and the pressixre. 

In order to be able to completely describe a pump combination as to its operating data, all that is now lacking is the calculation of the maximum cut-in pressure for the Roots vacuum pump. Meant here is the conventional mode of operating the Roots pump at a full rotational speed, without bypass valve and a programmed fixed cut-in pressure (through a pressure switch or through a pressure measurement arrangement from the side of the plant, for example). 

To do any quantitative vacuum work, begin by characterizing your pumping system. Obtain from the vendor s literature the speed of the pump itself at different pressures. Calculate the conductance of the connecting tubing and manifold, and then the speed of the system. Plot the pumping capacity (speed times pressure) versus pressure, as shown in Figure 13.6. 

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