Piping for metering orifi ces with nozzle-mix burners (with premix
burners, install orifi ce holder between atmospheric regulator
and mixer). One portable manometer can be used for all orifi ce
diff erential readings.
CHANGING ORIFICES
1. Turn off gas supply.
2. Remove orifi ce plate size tag.
3. Remove cover screws and cover.
4. Loosen internal spring holding screw.
5. Remove orifi ce plate.
6. Install new orifi ce plate.
7. Tighten internal spring holding screw.
8. Replace cover and cover screws.
9. Attach new orifi ce plate size tag.
10. Perform leak test to verify no leakage.
FIELD SETUP
1. Light burner. Adjust regulator and limiting orifi ce 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 orifi ce holder pressure tap momentarily to fl ush
out condensate and dirt.
4. Connect a manometer, with its equalizing valve open, to orifi ce
holder taps. Slowly open these taps; then slowly close the
equalizing valve, taking care not to "blow" the manometer.
5. Adjust limiting orifi ce valve for proper gas fl ow reading.
Using example (from "Selection," page 1):
If actual high fi re air pressure on gauge is 14 osi, air fl ow is
27,000 × √14/16 = 25,260 cfh and corresponding natural gas
fl ow should be 2526 cfh.
Adjust limiting orifi ce gas valve until manometer across the
#2400 plate shows 3.88"wc: (2526/2400)
2
× 3.5. (If using an
8736-A Manometer, its right hand scale [ specifi cally for 8697
Metering
Orifi ces] could be used--in this case 2526/2400 = 1.05
scale factor.)
Bulletin 8697
Page 17
TABLE C. Gas Data
TABLE D. Average Recovery % of Tap Diff erential
Btu
Correct
Gas
per
Air/Gas
Flow
Kind of Gas
Gravity cu ft
Ratio
Factor
§
Natural gas
0.6 1060 10
1.00
Coke Oven gas
0.4 570 5.45 1.22
Propane 1.5
2500
23.8
0.63
Butane 2.0
3210
30
0.55
Air 1.0
—
—
0.77
Oxygen
1.1 —
— 0.74
* 00 is a blank plate without orifi ce
† For pressure and temperature conditions other than 14.397 psia and 80°F, see
Sheets 8697-3 and -5.
Natural gas capacity at 3½ "w.c. dp is the plate number.
‡ High Beta ratio; normally used for air to prove fl ow only.
For oxygen, specify 8697- -C-plate #. Use oxygen-cleaned metal tubing and pipe
to an oxygen-approved diff erential-pressure gauge. Use only for line pressure at
or below 25 psig.
§ Capacity factor of a given orifi ce relative to same orifi ce with natural gas.
Corrosive to brass.
Average
Permanent
ID Recovery
Pressure
Loss
1st 15 85
2nd 17 83
3rd 20 80
4th 23 77
5th 27 73
6th 32 68
7th 36 64
The pressure recovery for any specifi c orifi ce/holder
combination depends on its position in the group of seven
standard IDs available for its pipe size.
EXAMPLE:
36% pressure recovery is possible with an 8697-1-810
or with an 8697-7-12450 (as well as the 7th ID in all other pipe
sizes). This means that when the pressure taps show a 3.5"wc
pressure diff erential, the permanent pressure loss is (100 – 36) or
64% of 3.5 or 2¼ "w.c.
Setup | Metering Orifice
