North American TwinBed ® II Fuel Tube Adjustment & Information
Sheet 4343-11
Slow air-gas mixing
Fast air-gas mixing
Gas entrance
Mixing rate adjustment
Cooling air passage
COOLING AIR The cooling air cools and protects the fuel tube. Flow should be set with the burners in stop cycle so that backpressure is con- stant. Adjust the cooling air butterfly valve to obtain setting. Pilot and cooling air schematic is shown on Sheet 4343-3. "Pressure drop" is drop in air pressure across the fuel tube.
FUEL TUBE ADJUSTMENT TwinBed II sizes -9, -10, -12-A, and -12-B have fuel tubes with a mixing rate adjuster at the back of the tube. The tube has two passages used to introduce gas into the main air flow. One pas- sage is for slow air/gas mixing and the other for fast air/gas mixing. With the adjuster backed out, the gas flows through both slow and fast air/gas mixing passages. When the adjuster is fully extended, the gas flows through the fast air/gas mixing passages only. Note: Screwing the adjuster fully extended may limit gas flow and maximum firing rate. See page 2 for gas flow graphs.
TB-II Size Flow (scfh)
-7, -8-A, -8-B
-9 thru -12-B
700
1000
Pressure drop "w.c.
1"
1"
Made with FlippingBook flipbook maker