Table 5 Ð Rated Gas Inputs at Indicated Manifold Pressures
| NUMBER | GAS SUPPLY PRESSURE | MANIFOLD | NATURAL GAS | PROPANE* | ||||||
UNIT |
| (in. wg) |
| PRESSURE | |||||||
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581B | OF | Natural | Propane | (in. wg) | Ori®ce | Heating Input | Ori®ce | Heating Input | |||
ORIFICES | |||||||||||
|
| Min | Max | Min | Max | Natural | Propane | Drill Size | (Btuh)² | Drill Size | (Btuh)² |
| 2 | 4.0 | 13.6 | 5.0 | 13.0 | 3.5 | 3.5 | 33 | 72,000 | 43 | 72,000 |
3 | 4.0 | 13.6 | 5.0 | 13.0 | 3.5²² | 3.5²² | 33 | 115,000²² | 43 | 115,000²² | |
| 3 | 5.0 | 13.6 | 5.0 | 13.0 | 3.5 | 3.5 | 30 | 150,000 | 38 | 150,000 |
*When a 581B unit is converted to liquid propane (LP), the burners must be modi®ed with accessory LP Kit.
²Based on altitudes from sea level up to 2000 ft above sea level. For altitudes above 2000 ft, reduce input rating 4% for each 1000 ft above sea level. In Canada, from 2000 ft above sea level to 4,500 ft above sea level, derate the unit 10%.
**581B036 with 150,000 Btuh input not available.
²²581B036115 at high ®re operation. At low ®re, manifold pressure is 1.8 in. wg, and heating input is 82,000 Btuh.
Table 6 Ð Altitude Compensation* Ð Units
| 72,000 AND 115,000 | 150,000 BTUH | ||
| BTUH NOMINAL INPUT | NOMINAL INPUT | ||
ELEVATION | Natural | Liquid | Natural | Liquid |
(ft) | Gas | Propane | Gas | Propane |
| Ori®ce | Ori®ce | Ori®ce | Ori®ce |
| Size² | Size² | Size² | Size² |
33 | 43 | 30 | 38 | |
2,000 | 34 | 43 | 30 | 39 |
3,000 | 35 | 44 | 31 | 40 |
4,000 | 36 | 44 | 32 | 41 |
5,000 | 36 | 44 | 33 | 42 |
6,000 | 37 | 45 | 34 | 43 |
7,000 | 37 | 45 | 35 | 43 |
8,000 | 38 | 46 | 36 | 44 |
9,000 | 39 | 47 | 37 | 44 |
10,000 | 41 | 48 | 38 | 45 |
11,000 | 43 | 48 | 39 | 45 |
12,000 | 44 | 49 | 40 | 46 |
13,000 | 44 | 49 | 41 | 47 |
14,000 | 45 | 50 | 42 | 47 |
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*As the height above sea level increases, there is less oxygen per cubic foot of air. Therefore, heat input rate should be reduced at higher altitudes.
²Ori®ces are available through your local distributor or branch.
NOTE: The gas manifold is equipped with a plug located ap- proximately 5 in. down from the gas valve which may also be used to connect the manometer.
3.Record number of seconds for gas meter test dial to make one revolution.
4.Divide number of seconds in Step 3 into 3600 (number of seconds in 1 hour).
5.Multiply result of Step 4 by the number of cubic ft shown for one revolution of test dial to obtain cubic ft of gas ¯ow per hour.
6.Multiply result of Step 5 by Btu heating value of gas to obtain total measured input in Btuh. Compare this value with heating input shown in Table 1. (Consult the local gas supplier if the heating value of gas is not known.)
EXAMPLE: Assume that the size of test dial is 1 cubic ft, one revolution takes 33 seconds, and the heating value of the gas is 1050 Btu/ft3, then proceed as follows:
1.33 seconds to complete one revolution.
2.3600 4 33 = 109
3.109 x 1 = 109 ft3 of gas ¯ow/hr
4.109 x 1050 = 114,450 Btuh input
If the desired gas input is 115,000 Btuh, only a minor change in the manifold pressure is required.
Observe manifold pressure and proceed as follows to adjust gas input:
1.Remove cover screw over regulator adjustment screw on gas valve. See Fig. 31.
2.Turn regulator adjustment screw clockwise to increase gas input, or turn regulator adjustment screw counter- clockwise to decrease input. Manifold pressure must be between 3.2 and 3.8 in. wg on
WARNING: Unsafe operation of the unit may result if manifold pressure is outside this range. Personal in- jury or unit damage may result.
3.Replace cover screw cap on gas valve.
4.Turn off gas supply to unit.
5.Remove manometer from pressure tap.
6.Replace pipe plug on gas valve or manifold.
7.Turn on gas to unit.
8.Check for leaks.
Fig. 31 Ð Burner Tray Details
Measuring Manifold Pressure Ð LP Gas Units
The main burner ori®ces on LP gas unit are sized for the unit rated input when the manifold pressure is 3.5 in. wg (high- ®re on
Proceed as follows to adjust gas input on an LP gas unit:
1.Turn off gas to unit.
2.Remove pipe plug on outlet of gas valve or manifold.
3.Connect manometer.
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