T
urndown Ratio =
P
1
= (Turndown Ratio)
2
P
2
0.25"w.c.
3
2
= 2.25"w.c.
At this pressure, -02 tip capacity can be calculated as follows:
Q
2
= Q
1
Q
2
for -02 tip = 22 000 at 5"wc (from capacity chart below)
22 000
= 14 800 Btu/h HHV.
Q
2
for -01 tip = 34 000
= 22 800 Btu/h HVV.
If the -02 tips are selected, 10 are required for the desired
capacity (10
14 800 Btu/h HHV = 148 000 Btu/h HHV). From
Bulletin 3065, a 3065-3-11 Mixer, with a capacity of 1550 scfh
air at 2.5"w.c. mixture pressure will suffi
ce. This mixer has a
1½
"
pipe size outlet; so fabricate the blast tip manifold from 1
½
" pipe.
Blast Tips
Sheet 4622/4624
4622 Cast Iron and 4624 Stainless Steel Blast Tips are small, self-
piloted premix burners. Mounted on pipe manifolds, they are well
suited for such applications as corebox and mold heating. They
burn natural or LP gases.
Operation.
For longest tip life, operate blast tips on or near
stoichiometric ratio about 4"w.c. mixture pressure. For added
capacity, they can be run slightly rich in the presence of
secondary air. To avoid fl ashback, mixture pressure should not
drop below 0.25"w.c. Maximum mixture pressure for stability is
over 10"w.c.
Installation.
Tips should be threaded into half couplings welded
to pipe manifolds, spaced closely enough for uniform heating.
(4622-02-P Blast Tips with tapered, plain shank, are press-fi t into
pipe manifolds and welded.) Minimum tip-to-work spacing, for
uniform non-impingement heating, is 4" on stoichiometric ratio at
4"w.c. mixture pressure. Shorter tip-to-work spacing can be used
if impingement heating is desired.
Tip can be fed from either 3065 Aspirator Mixers or 3070
Inspirators. Manifold pipe size generally should be the same as
the mixer outlet. On end-fed manifolds, allow fi ve pipe diameters
between the mixer and fi rst blast tip.
Maximum ambient temperature for 4622 tip is 300°F; 4624 tips
will withstand 800°F.
Selection Example:
Select blast tips and an aspirator mixer for
148 000 Btu/h HHV release on natural gas. Tips are to operate
over 3:1 turndown on stoichiometric ratio.
Minimum permissible mixture pressure is 0.25"w.c., therefore
required high fi re mixture pressure to obtain 3:1 turndown is
based on the following equation:
P
2
P
1
P
1
P
2
2.25"
5"
2.25"
5"
ENERG
Y | C
OMBUSITION
