Document ID: chunk:federal_register_of_legislation:F2011C00805:reg:120:p10
Version: federal_register_of_legislation:F2011C00805
Segment Type: reg
Provision Reference: reg 120 (pt 10/23)
Character Range: 260723–263713

critical flow. The variable mixture flow rate of dilution and exhaust gas is maintained at sonic velocity which is directly proportional to the square root of the gas temperature. Flow is continually monitored, computed and integrated throughout the test.

         The use of an additional critical-flow sampling venturi ensures the proportionality of the gas samples taken. As both pressure and temperature are equal at the two venturi inlets the volume of the gas flow diverted for sampling is proportional to the total volume of diluted exhaust-gas mixture produced, and thus the requirements of this Annex are met.

Figure 5/3

Constant volume sampler with positive displacement pump (PDP-CVS)

Figure 5/4

Constant volume sampler with critical-flow venturi (CFV-CVS System)

         3.2.2. Figure 5/4 is a schematic drawing of such a sampling system. Since various configurations can produce accurate results, exact conformity with the drawing is not essential. Additional components such as instruments, valve, solenoids, and switches may be used to provide additional information and co-ordinate the functions of the component system.

         3.2.3. The collecting equipment consists of:

         3.2.3.1.  a filter (D) for the dilution air, which can be preheated if necessary: the filter shall consist of activated charcoal sandwiched between layers of paper, and shall be used to reduce and stabilise the hydrocarbon background emission of the dilution air;

         3.2.3.2.  a mixing chamber (M), in which exhaust gas and air are mixed homogeneously;

         3.2.3.3.  a cyclone separator (CS), to extract particles;

         3.2.3.4. two sampling probes (S1 and S2) for taking samples of the dilution air, as well as of the diluted exhaust gas;

         3.2.3.5. a sampling critical-flow venturi (SV), to take proportional samples of the diluted exhaust gas at sampling probe S2 ;

         3.2.3.6. a filter (F), to extract solid particles from the gas flows diverted for analysis;

         3.2.3.7. pumps (P), to collect part of the flow of air and diluted exhaust gas in bags during the test;

         3.2.3.8. a flow controller (N), to ensure a constant flow of the gas samples taken in the course of the test from sampling probe S1; the flow of the gas samples shall be such that, at the end of the test, the quantity of the samples is sufficient for analysis (approx. 10 litres per minute);

         3.2.3.9. a snubber (PS), in the sampling line;

         3.2.3.10. flow meters (FL), for adjusting and monitoring the flow of gas samples during tests;

         3.2.3.11. quick-acting solenoid valves (V), to divert a constant flow of gas samples into the sampling bags or the vent;

         3.2.3.12. gas-tight, quick-lock coupling elements (Q), between the quick-acting valves and the sampling bags; the couplings shall close automatically on the sampling-bag side. As an alternative, other ways of transporting the samples to the analyser may be used