NOZZLE MIX SYSTEMS
16 osi on high fire
air
3D
5D
4 pipe dia.
metering orifice holder
2 osi drop
10 pipe dia. (min.)
10 osi
8 osi
16 osi on high fire
IF GAS SUPPLY PRESSURE IS LOW
If the supply pressure were only 10 osi, after a 2 osi pressure drop through the regulator, there would be only 8 osi available as outlet pressure. With 16 osi impulse the regulator will be wide open. The limiting orifice would have to be opened to get desired high fire ratio. If the air pressure were turned from 16 to 8 osi, the air flow would be reduced but the gas pressure would stay at 8 osi and the gas flow would stay the same resulting in the mixture going richer than desired. From this point down to low fire, the pressure would go down together, but the ratio would remain too rich. If this condition exists, it is best to raise the gas to 2 osi † greater than the air pressure. If this is not possible, a bleeder must be used.
† Or pressure drop for which the regulator size was selected.
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