Product Overview | Metering Orifice
Pressure taps should be on top or side of pipe to reduce prob- lems with dirt or condensate collecting in taps or manometer hose. When pressure is over 3 psi (207 mbar), remove hose barbs and install tube fittings to use metal tubing, rather than hose, between metering orifice and manometer. When metering oxygen, use 8694A-C versions, specially cleaned pipe and oxygen approved differential-pressure gauges and equipment. Models: 8694A- -A: Standard meter for air and fuel gases up to 60 psi (4.1 bar) pressure. 8694A- -C: Meter specially cleaned for oxygen service up to 60 psi (4.1 bar) pressure.
8694A and M8694A metering orifices provide repeatable gas flow measurements to industrial burners. They are compact inexpensive, and can be installed in individual burner gas lines to expedite adjustment of air/fuel ratio. 8694A meters can be used for burner setup and tuning. However, for air fuel ratio control with a pressure transmitter, refer to 8695 series metering orifices. The 8694A meters allow for easy checking of operation while burners are firing. Individual metering orifices are a great convenience on multi- burner furnaces, facilitating setting all burners the same or in de- sired gradients. Some installations add a larger 8694A Metering Orifice (upstream of the individual units) for continuous metering of total gas consumption in a zone or for the whole furnace. Many plants also use 8694A Metering Orifices in burner air lines to enable matching flows of combustion air and gas. FEATURES 8694A Sizes: ½" through 3" pipe size M8694A Sizes: ½" through 3" in ISO 7-Rp Nominal flows: 90 cfh to 11,950 cfh natural gas (2.5 m 3 /h to 444.6 m 3 /h) Body material: Standard = 6061 Aluminum Oxygen = Brass Plate Material: Standard = 304 SST Oxygen = Monel Seal: Viton Valves: Brass Maximum design pressure: 25 psi
SELECTING AN ORIFICE 1. Determine high fire air flow rate at the burner.
2. Determine corresponding gas flow rate: (For typical natural gas, divide air flow by 11 to determine gas flow.) See table below for other air/gas volume ratios. 3. Select next smaller orifice plate capacity from Table B1 (realize that the plate capacity is offered in a number of different pipe size holders).
Air/gas volume ratios
Fuel Gases natural gas
(10% XSAir and typical fuels)
11
Maximun design temperature: 200 °F Minimum design temperature: -20 °F
propane
26.2 33.6
butane
Flexibility: Each orifice assembly offers a choice of seven or eight plates that can be exchanged. This allows convenient on the job tailoring of the meter to fit its requirements. INSTALLATION 10 Straight clean pipe diameters upstream, 4 diameters down- stream, without valves or fittings. For maximum accuracy, readings must be corrected for:
Example: 1. A 4422-5 Burner passes 9,050 cfh air at 16 osi (assuming 16
osi represents "high fire" for this example). 2. Corresponding natural gas flow is 823 cfh.
3. A #675 plate is preferred because its higher required pressure drop--approximately 5"w.c.--means low fi re readings will be easier and more accurate. The 4422-5 Burner has a 1½" gas connection; a #675 plate is offered in the 8694A-3, so an 8694A-3 Metering Orifice may be the most convenient for this job.
gas (or air) line pressure gas (or air) temperature barometric pressure See Chart 1 and 2 for correction factors
Observe straight pipe run requirements.
Bulletin 8694A Page 2
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