OOGALGAZ. DERGiSi SAYI. 27 Orifice Air Gas Figıwe 2a. J121 Valve To burner Orifice A schemacic diagram illuscracing chis mechanism is given in Figure 2a. 2.2. ELECTRO-MECHANICAL SYSTEM These syscems comprise a square porc valve in ehe air line, a micro-racio valve in ehe gas !ine and an electric drive motor. The valves are mechnanically coupled by fully adjuscable linkages to ehe motor. As ehe motor curns, boch valves are opened or closed togecher. A schemacic diagram which illuscraces ehe mechanism is given in Figure 26. 2.3. ELECTRONIC SYSTEM This syscem ucilises chermiscors placed in ehe air/gas flow lines to sense changes in ehe flow races. Any imbalance in ehe flow race racio resulcs in ehe air valve being driven, or corde for a more accurace and reliable conc- recced, chus bringing ehe syscem back to rol of ehe valve which can take inco ac- ehe correct AGR. counc ehe valve dynamics and it is in chis concext thac ehe presenc scudy is based. 2.1. MECHANICAL SYSTEM These syscem types comprise a double diaphragm pneumatic ratio control valve in which ehe air and gas flows are inferred by measuring ehe differencial pressures developed across orifıce plates in both ehe aiı and gas lines. Motor Gas Valve To burner· Air Valvt> A schematic diagram which illustrates ehe electronic syscem is given in Figure 2c. 3. EVALUATION OF EXISTING SCHEMES in chis seccion ehe rest procedure chat has been adopced is described and ehe relacive performances ofehe three basic AGR concrol schemes under consideration are evaluated. Valve Gas Tl�errrıistor holder Valve Figure 2b,2c. L.._ ___ _ ____ _ __ _ 86
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