Capacity | Radiant Tube Gas Burners
Table 1b. Primary Air Screw Adjustments Required for 20%, 30% and 40% Primary Air
Adjusting Screw Turns Open
4725-2 4725-3 4725-4 4725-5 4725-6
20% Primary Air, 87.5% rated capacity 30% Primary Air, 100% rated capacity 40% Primary Air, 117% rated capacity
Full Closed
0 4
0
0 3
0 3
0
—
6 ½
7
Full Open
13+
13+
12+
6 ½
10+
AIR CAPACITY
4725- -G Burners include a glow pilot and spark plug. A 6000 volt transformer is required. After lighting, the spark should be turned off to prolong electrode life. Spark distributor systems can be used with this burner. 4725- -M Burners have manually ignited glow pilots, with a special lighter hole closing device to stop air infiltration. CONTROL AND ADJUSTMENT Burner must be lighted at low fire (1 osi max). Air pressure on 4725- -G and 4725- -M must not go below values in Table 2 even with on-off control. Refer to Sheets 4725-1 and 4725-4 for additional instructions and requirements. Accurate air/gas ratios can be determined by using 8697 Metering Orifices in the fuel and air lines, or by Orsat flue gas analysis.
Capacities in Table 1a are for burners with 30% primary air. Burners are shipped with the primary air adjusting screw closed, corresponding to 20% primary air and 87.5% of Table 1a capacities.
Primary air may require adjustment for smooth operation on some tube configurations.
Wide open adjustment of primary air screw increases primary air to about 40% and total air capacity to about 117% of Table 1a figures. Table 1b shows approximate number of turns of air adjusting screw for 30% and full open primary air. Installations using greater than 30% primary air should have blower capac- ity increased accordingly. PREHEATED AIR For air preheats to 900°F use 4725- -EH described on Sheet 4725-5. PROPANE Evenglow burners are suitable for use with propane gas, but the primary air must be adjusted wide open to avoid soot formation. LIGHTING ARRANGEMENTS 4725- -E Direct Spark Ignited Burners. The main flame is lighted by a simple electrode igniter located behind the flame front for cool long-life operation. The spark should be turned on before the burner gas valve is opened; after the burner is lighted, the spark must be turned off for proper burner operation. During the ignition period, a continuous 6000 volt spark is required. Spark distributor systems cannot be used with 4725- -E Burners. 4725- -G and 4725- -M Gas Piloted Burners include gas pilots that glow, permitting the furnace operator to see at a glance if pilots are burning. A mixture pressure of 3"w.c. produces a bright red glow, visible after 2 minutes’ warm-up. The pilot has 15,900 Btu/h HHV capacity at the maximum allowable mixture pressure of 3"w.c. and requires a 4031 Mixer.
Table 2. MINIMUM BURNER AIR PRESSURE with gas pilots. Add tube backpressure . 4725- -G or -M Glowing Pilot
Pilot Operated Non-glow
Burner Size
at 3"w.c. mixture pressure at 1 ½ "w.c. mixture pressure
-2 -3 -4 -5
0.6 osi 0.3 osi 0.3 osi 0.2 osi
0.3 osi 0.2 osi 0.2 osi
‡
Table 3. MINIMUM GAS PRESSURE FACTORS for natural gas. Consult North American for factors for other gases.
4725- -E, -G, or -M Burner Size
To find the approximate minimum natural gas pressure required across the burner for the capacity ratings of Table 1, multiply the high fire air pressure across the burner by the factor shown. See example under "Selection." Do not use this table to set air/gas ratios.
Factor
-2 -3 -4 -5
0.06 0.12 0.06 0.12 0.26
-6-E
† When mounting on a tube with I.D. less than 5 ¾ ", a 1⁄8 " thick gasket is required between the burner mounting flange and the radiant tube flange. ‡ Cannot be operated non-glow because 3"w.c. mixture pressure is required.
Bulletin 4725 Page 2
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