Document ID: chunk:federal_register_of_legislation:F2023C00229:reg:9:p35
Version: federal_register_of_legislation:F2023C00229
Segment Type: reg
Provision Reference: reg 9 (pt 35/71)
Character Range: 307220–310181

of V0. Values of m will vary from one pump to another. Particulate influx over time will cause the pump slip to decrease, as reflected by lower values for m. Therefore, calibration shall be performed at pump start-up, after major maintenance, and if the total system verification (Section 2.4) indicates a change of the slip rate.

2.3.                            Calibration of the Critical Flow Venturi (CFV)

              Calibration of the CFV is based upon the flow equation for a critical venturi. Gas flow is a function of inlet pressure and temperature, as shown below:

              where,

              Kv   = calibration coefficient

              pA   = absolute pressure at venturi inlet, kPa T = temperature at venturi inlet, K
2.3.1.                        Data analysis

              The air flowrate (Qs) at each restriction setting (minimum eight settings) shall be calculated in standard m3/min from the flowmeter data using the manufacturer's prescribed method. The calibration coefficient shall be calculated from the calibration data for each setting as follows:

              where,

              Qs   = air flow rate at standard conditions (101,3 kPa, 273 K), m3/s T = temperature at the venturi inlet, K
              pA   = absolute pressure at venturi inlet, kPa

              To determine the range of critical flow, Kv shall be plotted as a function of venturi inlet pressure. For critical (choked) flow, Kv will have a relatively constant value. As pressure decreases (vacuum increases), the venturi becomes unchoked and Kv decreases, which indicates that the CFV is operated outside the permissible range.

              For a minimum of eight points in the region of critical flow, the average Kv and the standard deviation shall be calculated. The standard deviation shall not exceed ± 0,3 % of the average KV.

2.4.                            Total system verification

              The total accuracy of the CVS sampling system and analytical system shall be determined by introducing a known mass of a pollutant gas into the system while it is being operated in the normal manner. The pollutant is analysed, and the mass calculated according to Annex III, Appendix 2, Section 4.3 except in the case of propane where a factor of 0,000472 is used in place of 0,000479 for HC. Either of the following two techniques shall be used.

2.4.1.                        Metering with a critical flow orifice

              A known quantity of pure gas (carbon monoxide or propane) shall be fed into the CVS system through a calibrated critical orifice. If the inlet pressure is high enough, the flow rate, which is adjusted by means of the critical flow orifice, is independent of the orifice outlet pressure (≡ critical flow). The CVS system shall be operated as in a normal exhaust emission test for about 5 to 10 minutes. A gas sample shall be analysed with the usual equipment (sampling bag or integrating method), and the