Setup | Metering Orifice
TABLE C. Gas Data
TABLE D. Average Recovery % of Tap Differential
Btu per
Correct Air/Gas Ratio
Average
Permanent
Gas
Flow Factor §
ID 1st
Recovery Pressure Loss
Kind of Gas Natural gas
Gravity cu ft
15 17
85 83 80 77 73 68
0.6 1.5 2.0 1.0
1060 2500 3210
10
1.00 0.63 0.55 0.77
2nd 3rd 4th 5th 6th 7th
Propane Butane
23.8
20 23 27 32
30 —
Air
—
Oxygen
1.1
—
—
0.74
FIELD SETUP 1. Light burner. Adjust regulator and limiting orifice valve per their instructions. 2. Attach a manometer or quality air pressure gauge to burner air connection. Set burner air valve for desired pressure. 3. Open each orifice holder pressure tap momentarily to flush out condensate and dirt. 4. Connect a manometer, with its equalizing valve open, to orifice holder taps. Slowly open these taps; then slowly close the equalizing valve, taking care not to "blow" the manometer. 5. Adjust limiting orifice valve for proper gas flow reading. Using example (from "Selection," page 1): If actual high fire air pressure on gauge is 14 osi, air flow is 27,000 × √14/16 = 25,260 cfh and corresponding natural gas flow should be 2526 cfh. Adjust limiting orifice gas valve until manometer across the #2400 plate shows 3.88"w.c.: (2526/2400) 2 × 3.5. (in this case 2526/2400 = 1.05 scale factor.) 36 64 The pressure recovery for any specific orifice/holder combination depends on its position in the group of seven standard ID's available for its pipe size. EXAMPLE: 36% pressure recovery is possible with an 8697-1-810 (as well as the 7th ID in all other pipe sizes). This means that when the pressure taps show a 3.5"w.c. pressure differential, the permanent pressure loss is (100 – 36) or 64% of 3.5 or 2¼"w.c.
† For pressure and temperature conditions other than 14.397 psia and 80 °F, see Chart 1 and 2.
Natural gas capacity at 3½"w.c. dp is the plate number. ‡ High Beta ratio; normally used for air to prove flow only.
For oxygen, specify 8694A--C-plate #. Use oxygen-cleaned metal tubing and pipe to an oxygen-approved differential-pressure gauge. Use only for line pressure at or below 60 psig. § Capacity factor of a given orifice relative to same orifice with natural gas. Corrosive to brass.
Piping for metering orifices with nozzle-mix burners (with premix burners, install orifice holder between atmospheric regulator and mixer). One portable manometer can be used for all orifice differential readings.
CHANGING ORIFICES 1. Turn off gas supply. 2. Remove orifice plate size tag. 3. Remove one flange bolt. 4. Use Jack screw if necessary. 5. Remove orifice plate. 6. Install new orifice plate. 7. Replace flange bolt. 8. Attach new orifice plate size tag. 9. Perform leak test to verify no leakage.
Bulletin 8694A Page 7
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