Product Overview | High Pressure Inspirator
3070 Inspirators supply a fuel / air mixture to open or sealed- in premix burners by using the energy in high pressure natural gas to induce and mix with combustion air. Gas inlet pressures between 10 and 30 psi are most common but gas pressures up to 100 psi gas can be used. The primary advantage of inspirator mixers is they work without the need of a combustion air blower, which reduces the cost and complexity of a premix burner system. They are ideal for use with small spot heating premix burners.
Generally to use propane in a 3070, size a smaller spud size and use a higher gas pressure if possible. Expect that the mixture pressure delivered to the burner will likely be lower than when using natural gas. A good option for using propane, butane or low pressure gases in an open-air burner is to use a North American 4696 torch. This is a packaged unit that uses 40-80 psi compressed air to inspirate combustion air into an inspirator mixer body where it’s mixed with almost any gaseous fuel including Natural gas, Pro- pane, or Butane and delivered to the burner nozzle. See Bulletin 4696 for details. Attempting to operate 3070 mixers with Hydrogen fuel (or fuels with high percentages of Hydrogen) will incur a high risk of the flame flashing back into the mixer. This can be dangerous to personnel as well as damaging to the mixer and burner. STRAIGHT PIPE RUN RECOMMENDATIONS While it is common to attach a burner nozzle directly to the end of a 3070 mixer, the burner may have a slightly wider stability range if a pipe nipple at least 5 pipe diameters long is placed between the mixer and the burner nozzle. This provides extra time for the air and gas mixture to become more uniform before entering the burner nozzle. INSPIRATOR MIXERS FOR OTHER APPLICATIONS 3070 Inspirator mixers can be used to replace main air blowers where it is difficult to use a traditional blower. In this application the gas is replaced with compressed air which draws additional air into the mixer. See Sheet 3070-1 for details. OTHER MIXERS (ASPIRATORS) FOR PREMIX BURNERS While they require combustion air blowers, aspirator mixers such as the North American 3065 offer many advantages over inspirator mixers. With aspirator mixers the air pulls the gas into the mixer. — Aspirator mixers can provide higher mixture pressures than Inspirator mixers so the burners have higher burner capacities and resistance to flashback. More turndown is also possible for better temperature control. — There are no sizing problems using Propane and Butane. — The gas pressure does not have to be nearly as high, and if sized correctly the gas pressure can be atmospheric pressure at the aspirator mixer inlet. — The burner air/fuel ratio is controlled with a cross connected regulator which provides much better control than is possible with a 3070.
High Pressure Gas
Air/Gas premix to burner
Inspirated Air
Desired air/gas ratio is set with the air disc at high fire and is maintained reasonably throughout the turndown range, as long as the combustion chamber pressure is fairly steady. A gas ori- fice in the spud is aligned with the machined throat in the body to ensure proper air inspiration at the highest possible mixture pressures. Unfortunately there are disadvantages that limit the applica- tions where inspirator mixers can be used. Available turndown depends on mixture pressure, which in turn depends on gas and furnace pressures. Inspirators are primarily on-off devices. If the available gas pressure is to low, the gas will not be able to pull enough air into the mixer to prevent flashback.
As the gas pressure increases so does the noise produced from the mixers gas nozzle.
Inspirator capacity is affected significantly by the type of installation and pressure conditions within the combustion chamber: Negative pressures (draft) increase inspirator capacity and retard flashback. Positive pressures reduce capacity, and probability of flashback is greater. At neutral furnace pressures, flashback normally will not occur at mixture pressures above 0.25"w.c. for natural gas. FUELS OTHER THAN NATURAL GAS Propane requires more air per cfh of fuel than natural gas. So it's harder for propane to draw enough air into the an inspirator mixer. While Propane has been successfully used with 3070 mix- ers, Fives North American does not have propane sizing tables or encourage using propane in 3070 mixers.
Bulletin 3070 Page 2
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