Calculation of the Back-Pressure Length

The back-pressure length can be derived from the pressure Eq. 7.2 with a simple transformation  

The optimum efficiency during pressure generation is generally achieved at A 0.5. In this case, three times the length in relation to the left-hand element is required to generate the pressure. The back-pressure rises fast as the throughput per revolution increases. At A = 0.8, the back-pressure is already 9 times as long as the left-hand element. 

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