Calculations, Performance Curves, and Other Measurements in Jet Systems

3 Calculations, Performance Curves, and Other Measurements in Jet Systems 

We have discussed the American system inches of mercury (inches Hg) in Chap. 10, How Instruments Work. Of more immediate interest is Table 23.1. To do any sort of vacuum calculation, we need to convert to the absolute system, in millimeters of mercury (mm Hg). Unfortunately, we also need to correct measurements made with an American-type (inches Hg) vacuum gauge for atmospheric pressure. You can interpolate between the two sets of data in Table 23.1, to correct for almost the entire range of typical atmospheric pressures. 

We will need to use this table to calculate a jet s compression ratio when we measure vacuum pressures with an American-type (inches Hg) gauge. 

When considering the performance of a vacuum jet, we must first consider the jet s overall compression ratio. To calculate a jet s compression ratio  

Measure the jet s suction pressure and convert to millimeters of mercury, as shown in Table 23.1. 

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