Document ID: chunk:federal_register_of_legislation:F2024L00446:reg:16:p43
Version: federal_register_of_legislation:F2024L00446
Segment Type: reg
Provision Reference: reg 16 (pt 43/108)
Character Range: 1004987–1008083

will seriously affect the accuracy of the calibration and shall therefore be prevented.

Figure A5/7
CFV calibration configuration
              3.4.3.3.1. The variable-flow restrictor shall be set to the open position, the suction device shall be started and the system stabilized. Data from all instruments shall be collected.
              3.4.3.3.2. The flow restrictor shall be varied and at least eight readings across the critical flow range of the venturi shall be made.
              3.4.3.3.3. The data recorded during the calibration shall be used in the following calculation:
              3.4.3.3.3.1. The air flow rate Qs at each test point shall be calculated from the flow meter data using the manufacturer's prescribed method.
              Values of the calibration coefficient shall be calculated for each test point:
           where:
           Qs is the flow rate, m3/min at 273.15 K (0 °C) and 101.325, kPa;
           Tv is the temperature at the venturi inlet, Kelvin (K);
           Pv is the absolute pressure at the venturi inlet, kPa.
              3.4.3.3.3.2. Kv shall be plotted as a function of venturi inlet pressure Pv. For sonic flow Kv will have a relatively constant value. As pressure decreases (vacuum increases), the venturi becomes unchoked and Kv decreases. These values of Kv shall not be used for further calculations.
              3.4.3.3.3.3. For a minimum of eight points in the critical region, an arithmetic average Kv and the standard deviation shall be calculated.
              3.4.3.3.3.4. If the standard deviation exceeds 0.3 per cent of the arithmetic average Kv, corrective action shall be taken.
              3.4.4. Calibration of a subsonic venturi (SSV)
              3.4.4.1. Calibration of the SSV is based upon the flow equation for a subsonic venturi. Gas flow is a function of inlet pressure and temperature, and the pressure drop between the SSV inlet and throat.
              3.4.4.2. Data analysis
              3.4.4.2.1. The airflow rate, Qssv, at each restriction setting (minimum 16 settings) shall be calculated in standard m3/s from the flow meter data using the manufacturer's prescribed method. The discharge coefficient Cd shall be calculated from the calibration data for each setting using the following equation:
           where:
                  QSSV  is the airflow rate at standard conditions (101.325 kPa, 273.15 K (0 °C)), m3/s;
           T is the temperature at the venturi inlet, Kelvin (K);
           dv is the diameter of the SSV throat, m;
                  rp is the ratio of the SSV throat pressure to inlet absolute static pressure,
                     ;
                  rD is the ratio of the SSV throat diameter dV to the inlet pipe inner diameter D;
                  Cd is the discharge coefficient of the SSV;
                  pp is the absolute pressure at venturi inlet, kPa.
              To determine the range of subsonic flow, Cd shall be plotted as a function of Reynolds number Re at the SSV throat. The Reynolds number at the SSV throat shall be calculated using the following