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 off ers more sizing
options if fi eld 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
fi nd 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.
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 fi nd 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
orifi ce 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
.
Eff ective mixer throat area = for a
3065-7-S38
= 2.652 sq. in.
(from
Table 3B
)
(A), Throat area, unknown mixer
=
Capacity, unknown mixer
Throat area, known mixer Capacity, known mixer
(A)
2.652
23,000 scfh
21,000 scfh
=
From
Table 3B
use
3065-7-S34
mixer.
A = 2.90 sq. in.
3065 Sizing Examples continued
Bulletin 3065
page 14
