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Section No. 2.2.4 Revision No. 0 Date May 1, 1977 Page 7 of 17 • when the filter is aligned and the faceplate is in place, the four wing nuts are tightened just enough to prevent leak- age. Excessive tightening may cause the filter to stick to the gasket and result in permanent damage to the gasket. The entire motor assembly (sampler) is rotated and lowered to its normal operating position, Figure 4.2. 4.2 Operational Checks 4.2.1 Flow-Rate Measurements with Rtameter Equipped Sampler - t4ake flow-rate measurements while the sampler is at normal operating temperature. This requires a warmup time of at least 5 minutes before a valid measurement can be obtained. Connect the rotameter to the sampler, using the same tubing as was used to calibrate, and place or hold in a ver- tical position at eye level. Read the widest Dart of the float. Use the calibration chart to convert the reading to • cubic meters per minute rounded to the nearest 0.03 m3/min., see Figure 2.12. Flow rates are measured at the beginning and end of each sampling period. additional measurements at different times during the sampling period may be required in special instances, such as in those cases where nonlinear loading on the filter occurs. For example if the sampler is located tear a source which only o?orates for a specific period over the total 24-hour sampling period, flow measurements should be taken at the end of the specific period. Precautions to be taken when making flow-rate measure- ments include: 1. after connecting the rotameter to the sampler, ob- serve for at least one minute before taking a reading. I° a gradual change in flow rate is observed do not take a reading until equilibrium is reached. a y-radual chance will • usually be observed when the rotameter is at a substantially different temperature `rpm the sampler exhaust air and may require 2 to 3 minutes to equilibrate.