NOZZLE MIX SYSTEMS
REGULATOR SELECTION
To size a regulator, determine the required cfh of gas and pressure drop available at high fire. Divide required cfh by Table 2 Factor for available pressure drop. Select the smallest regulator with Table 1 (2 osi) capacity above this adjusted capacity. Never choose a regulator capacity based on more than 16 osi drop (even if more is available) EXAMPLES A nozzle-mix system requires 5000 cfh of natural gas. Gas inlet pressure is 12 osi; maximum air pressure at the burner is 8 osi. When cross-connected, outlet gas pressure is 8 osi at high fire; pressure drop across regulator is 12 – 8 = 4 osi. Table 2 factor for 4 osi is 1.41; 5000 cfh ÷ 1.41 = 3546 cfh. In the 0.6 sp gr column of Table 1, select a 7218-4 Regulator (rated at 4800 cfh.) If air pressure at the burner was 16 osi but available gas pressure was still only 12 osi, a bleeder would be required in the cross connection. For minimum bleed†, select regulator for required cfh directly from Table 1 (2 osi) capacities; then bleed cross-connected air impulse at high fire from 16 osi to 10 osi (12 osi available gas pressure minus 2 osi drop through regulator). For the required 5000 cfh in this example, select a 7218-5 from Table 1. If system was premix instead of nozzle-mix, regulator outlet pressure is zero, and pressure drop through the regulator would equal inlet gas pressure (12 osi). Table 2 factor is 2.45; 5000 ÷ 2.45 = 2040 cfh. Select a 7218-3 Regulator from Table 1.
Table 1. CAPACITIES scfh MAXIMUM WIDE OPEN with 2 osi drop through regulator and 2 psig inlet pressure Regulator gas gravity designation 0.6 1.5 7218-01 285 180 7218-0 540 341 7218-1 700 442 7218-2 1730 1090 7218-3 2800 1770 7218-4 4800 3030 7218-5 6900 4360 7218-6 9100 5750 7218-7 17600 11120
(For capacities at other drops, use square root law or Table 2 page 25.)
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