PREMIX SYSTEMS
clearance for pullling displace- ment rod
8666 Testip
1 ½ " or larger mixer
pressure tap
1⁄8 " pipe size
pressure tap on opposite side
2 pipe dia. recommended minimum
identification markings
If an elbow is used in this section, allow at least 2 pipe diameters on each side of the elbow.
last figure denotes rod size in 32nds of an inch
gas adjustment valve gas inlet
mixture
outlet
interchangeable displacement rod
air inlet
ADJUSTMENT OF PREMIX SYSTEMS
Adjust the high fire air/gas ratio by slowly turning the air valve to high fire position while adjusting the limiting orifice gas valve as needed to maintain the desired air/gas ratio. † Replace the valve cover. Adjust the low fire air/gas ratio. Turn the air to low fire (about ½ osi). If more or less gas is required, remove the regulator's gas diaphragm cover plug and use a screwdriver to turn the spring adjusting plug - clockwise* for more gas. Replace the cover plug. On sealed-in burners where flame is not visible, the following is recommended for a 1 ½ " or larger mixer. Drill and tap a 1⁄8 " hole in the pipe from mixer to burner; screw an 8666 Testip into this hole and light it so that you can see a sample of main burner flame. Adjust the mixer for the type of flame desired †, using the flame from the Testip as a guide. (A purple-tinged flame denotes a lean fire; a greenish-blue inner-cone denotes a rich flame) The Testip can be removed, the hole plugged, and the Testip used on other burners. Mixers have interchangeable displacement rods that permit changing mixer orifices to conform to field conditions or to get lower or higher mixture pressures (with consequent more or less suction, respectively). Rods can be interchanged without breaking piping. Recommended rod diameters are listed on Bulletin 3065 for burner(s)., type of gas, and air pressure involved. * For North American 7218 Regulators. Others may be different. † See "Judging Flames," page 61.
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