3065 Sizing Examples continued
Example E2: An existing system uses a 3065-5-17 mixer to feed four (4) 4682-2-A burner nozzles with a zero governor ratio control for natural gas. What mixer is needed if the burners are changed to four (4) 4682-2-D burner nozzles to increase the system capacity. — Since these are standard size burner nozzles with zero governor ratio control, use Table 2 . Find the -2-D burner row, move right and find the 4 burner column. Pick the 3065-6-18 mixer from the list. This is a new mixer size which requires larger pipe (but maybe a 3065-5-S_ will work) from Table 3B , the orifice throat area of a 3065-6-18 is (1.040 in2). A 3065-5-S15 is (1.055 in2). So use the 3065-5-S15 because only the mixer needs to be changed and not the piping. Note: The other system components still need to be checked to see if they are suitable for use with the higher capacity. Due to more pressure drop through the piping it may be necessary to cross connect the ratio regulator. Example G: Select a mixer for a 2,300,000 Btu/h (divide by 100= 23,000 scfh air) burner with 8 osi air and 4"w.c. mixture pressure. (zero governor ratio control for natural gas) Pressure drop across the mixer = 8 osi (14"w.c.) minus 4"wc mp = 10"w.c. — From the capacity Chart 1B , a 3065-8 with between a #56 and a #64 rod or a 3065-7-S with between no rod and a #38 rod (21,000 cfh capacity) could be used. For minimum cost and size, use a 3065-7-S .
Example C: Select a mixer for a 4682-6-C burner with 8 osi (14"w.c.) air and 8"wc mixture pressure. This arrangement necessitates a cross-connected regulator and high gas pressure because air pressure drop is <66% of its air pressure. — Capacity of a 4682-6-C at 8"w.c. mixture pressure is 1,200,000 Btu/h. (divide by 100= 12,000 scfh air) Pressure drop across the mixer = 8 osi (14"wc) minus 8"w.c. mp = 6"w.c. From the capacity Chart 1B , a 3065-6-S0 Mixer would serve the purpose, as would a 3065-7-20. For minimum cost and size (both mixer and burner nozzle are 3" NPT) use the 3065-6-S0 mixer. The gas pressure required upstream of the ratio regulator = 14" w.c. + 6"w.c. = 20" wc = 11.5 osi (use 12-16 osi) Example D: Select a mixer for 3,000 scfh air) burner with 8 osi air and 8"w.c. mixture pressure. (This arrangement necessitates a cross-connected regulator and 12-16 osi gas pressure.) Pressure drop across the mixer = 8 osi (14"w.c.) minus 8"wc mixture pressure = 6"w.c. — From the capacity Chart 1A , a 3065-3-S0 or a 3065-4-8 could be used. Which mixer to choose depends on a number of factors. - The 3065-3-S0 uses 1 ½ " pipe and the 3065-4-8 uses 2" pipe - If at any time the system capacity needs to be increased, the capacity of the 3065-4-8 can be increased by using a smaller displacement rod. The 3065-0-S0 with its -0 rod is already is at the maximum capacity. - In most cases pick the mixer with the same pipe size as the burner, but the 3065-4-8 mixer offers more sizing options if field conditions require a new displacement rod choice. Example E1: An existing system uses a 3065-5-17 mixer to feed four (4) 4682-2-A burner nozzles, with a zero governor ratio control for natural gas. What mixer is needed if the burners are changed to four (4) 4682-2-B burner nozzles to increase the system capacity? — Since these are standard size nozzles with zero governor ratio control, use Table 2 . Find the -2-B nozzle row move right and find the 4 nozzle column. Find the 3065-5-12 Mixer from the list. Since the mixers are both the 3065-5 size, only the displacement rod needs to be changed.
Effective mixer throat area = for a 3065-7-S38 = 2.652 sq. in. (from Table 3B )
(A), Throat area, unknown mixer = Throat area, known mixer
Capacity, unknown mixer Capacity, known mixer
(A) 2.652
23,000 scfh 21,000 scfh
=
A = 2.90 sq. in.
From Table 3B use 3065-7-S34 mixer.
Bulletin 3065 page 14
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