on the pressure depending on the measurement points at the pipe of inside diameter of 70.3 mm are presented in Fig. 2. The trends in this figure are rather clear. When
the pipe diameter is kept constant, the pressure rises directly with the air velocity. The rate of pressure increase varies with the air velocity. The rate of pressure rise
increases as the air velocity increases. Statistical analysis has shown that the effect of air velocity on the pressure was important at the 1% probability level. The effect of
the pipe length is also clear. At any constant velocity, the pressure decreases as the length of the pipe increases,namely, from the feeder point to the exit of the pipe. Pressure drop is the difference between the two pressures at the two measurement points. The values given in Fig. 2 can be evaluated with respect to the pressure drop. Pressure drop increases with an increase in air velocity. For example,pressure drop between the first pressure measurement point(PM1) and the last pressure measurement point (PM5) at the air velocity of 12.7 m/s is lower than that at 32.5 m/s.