NOZZLE MIX SYSTEMS
LIGHTING AND ADJUSTMENT
1. Light the burner. Follow the blower instructions to start the blower. All gas lines up to the 7218 Regulators must be purged. Before lighting any pilot or burner, make sure that all manual fuel valves are closed, and purge the firing chamber . Follow the pilot instructions light the pilot. Set the main air valve at the low fire position (1 or 2 osi air pressure). Open the limiting orifice gas valve 6 to 6½ turns. Open the upstream gas shutoff valves(s). If the burner does not light in a few seconds, close the nearest upstream gas shutoff valve to prevent accumulation of unburned gas, purge the chamber allowing sufficient time for a minimum of 4 changes of atmosphere, then open the limiting orifice gas valve one more turn and reopen the gas shutoff valve. Repeat this procedure until the main flame lights. 2. Adjust the high fire air/gas ratio. Slowly turn the air valve to high fire position while adjusting the limiting orifice gas valve as needed to maintain the desired air/gas ratio. Replace the limiting orifice valve cover. 3. (For 7218 only, not 7216) Adjust the low fire air/gas ratio only after step 2 is completed. Turn the air valve to low fire position. Remove the gas diaphragm cover plug on the bottom of the regulator. Use an Allen wrench to turn the spring adjusting plug clockwise for more gas, or counterclockwise for less gas, to obtain the desired air/gas ratio. † Replace the gas diaphragm cover plug. 4. (For 7218 only, not 7216) On-off control. To adjust the regulator for on-off control, turn the spring adjusting plug counterclockwise until the compression spring is completely relaxed. NOTE: While the soft seat in this regulator provides good closing characteristics with zero impulse pressure. It is not meant to be used as a shutoff valve. If the burner is to be held in a "off" cycle for periods which exceed normal cycle times, an approved shutoff valve must be installed to prevent fuel leakage. 5. Dual-fuel burners. When a nozzle-mix burner of the dual-fuel type is being operated on gas with atomizing air left on, the regulator must supply a constant amount of gas to match the atomizing air plus a varying amount to match the main air at any firing rate. To adjust the regulator for this situation, first operate on main air only and follow the instructions under nozzle-mix burners for making the cross-connection, adjusting the limiting orifice gas valve, and adjusting the bleed if any is required. Next turn off the main air (the flame will go out), and remove the gas diaphragm cover plug. Turn on the atomizing air at the pressure suggested for gas operation and screw the spring adjusting plug clockwise until the pilot relights the burner and the desired air/gas ratio is found.
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