Sizing 3065 Mixers Instructions
• For Standard North American premix burners:
Example C: to size a mixer for a burner running Natural Gas, that requires 6" wc @ 6,000 cfh air and using the classic air pressure to mixture pressure multiplier of 3.5X
North American 4651, 4659, and 4682 premix burners share the same capacity rating system but consult the individual burner bulletin and sheets for details and operating stability range. Not every size premix burner capacity is available for every burner nozzle type, or suitable to operate at every pressure on the sizing tables. — Table 1 shows mixer sizing recommendations for a single North American premix burner and Table 2 is for sizing multiple North American premix burners. As shown in the Table 1 header, the mixer inlet air pressure is assumed to be about 3.5X the mixture pressure. (for natural gas) Example A: Select a mixer for a single 4651-2-D burner with 16 osi (27.7"w.c.) air and 8"wc mixture pressure, with zero governor ratio control for natural gas. — Since this is a standard burner nozzle size with zero gover- nor ratio control, use Table 1. Find the -2-D burner and pick a 3065-2-0 mixer from the list to the left . Per Table 3A, the 3065-3-13 has the same mixer throat area, and offers more sizing options if field conditions require a new displacement rod choice.
ap = 6"w.c. X 3.5 = 21"w.c. air pressure p =21" wc - 6"w.c. = 15"w.c. p
— Use Chart 1 or Table 3 with the desired air flow and mixer p to identify the correct 3065 mixer to match other premix burners for use with zero governor ratio control. Note that Chart 1 does not list every size mixer available. — Table 3 shows the mixer air capacity @ 1” w.c. p, to find the right match, the air flow @ 15” w.c. p must be converted using the square root law to show the equivalent flow at 1" w.c. p.
p = 15"w.c. @ 6,000 cfh air
P 2 P 1
Solution: Q 2 = Q 1 x
1
Q 2 = 6,000 x
15
Example B: Select a mixer for feeding six (6) 4651-2-A burners, with zero governor ratio control for natural gas.
Q 2 = 1549 cfh air @ 1"
Using Table 3 : choose a 3065-5-16 mixer (with 2 ½ " connections), if 2" air piping is preferred then a 3065-4-S12 (with 2" connections) instead. Example D: An existing system has 20 small premix burners with a capacity of 500 cfh air each. The air pressure (ap) into the old mixer is 22"w.c. and the mixture (mp) is 7"w.c., pick a new compatible 3065 mixer to replace the old mixer.
— Since these are standard size burner nozzles with zero governor ratio control, use Table 2. Find the -2-A burner row move right and find the 6 burner column. Pick the 3065-6-20 Mixer from the list.
• For other premix burners if the required burner capacity, air pressure (ap) and mixture pressure (mp) is known:
— If the desired air pressure (ap) upstream of the mixer is not known, it can be estimated using the guidelines below.
- Total capacity = 20 x 500 cfh = 10,000 cfh air flow.
- Mixer p available = 22"w.c. - 7 w.c. = 15"w.c. p
• For Natural Gas, multiply the mixture pressure (mp) by 3.5
- Find mixer flow at 1.0“w.c. p to use Table 3
• For Manufactured or Coke Oven Gas, mixer air pressure (ap) = mixture pressure (mp) X 4.0
Note: the mixer air pressure is 3.1X the mixture pressure, so cross connect the ratio regulator. (22/7=3.1)
• If the available system air pressure is limited, a lower air pressure to mixture pressure multiplier (2.5X for example) can be used if the ratio regulator is cross connected and proper distance between the mixer and the burner is maintained.
1
Q 2 = 10,000 x
= 2582 cfh @ 1"w.c.
15
— From table 3A pick one of these mixers: 3065-5-S13 with 2 ½ " connections or 3065-6-16 with 3" connections. Pick depending on preferred pipe size.
— To find mixer p (differential pressure drop across mixer), subtract mixture pressure from air pressure ( p = ap - mp)
Bulletin 3065 page 5
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