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Gas
Firing
Flame
Rate
Tube
MBH
Nat.
300
5 ¼"
Nat
550
5 ¼"
Nat.
300
14"
Nat.
550
14"
LP
300
5 ¼"
LP
550
14"
* ∆P= Pressure drop. For this gas valve, ∆P= 1". Refer to the literature for the gas valve for more
information on pressure drops.
The high and low gas pressure switches must be set during installation (refer to Table 3 and Table 4). To
determine the setting of the low pressure gas switch (LPS), measure the manifold pressure (MP), inlet
pressure (IP) and the pressure between the valve (BV):
After the firing rate is determined, refer to the charts Table 3 or Table 4 on page 12 of this
manual. Multiply the manifold pressure necessary by 1.5 and set the High Gas Pressure Switch to reflect
that calculation.
Divide the manifold pressure by 2 and add the pressure drop across the valve.
Example: Natural Gas at 340 MBH
Required Manifold Pressure= 2.7"
Pressure drop across Honeywell valve=1.0"
HPS = 1.5*2.7"=4.0"
LPS = (2.7"/2) + 1.0"=2.35"
For other valves, refer to the manual for that specific valve for the pressure drop.
Warning: After the burner has been adjusted so that the burner is operating properly, the pressure
switches must be readjusted.
Using a monometer, measure the manifold pressure that was necessary to achieve the exact firing
•
rate necessary. Multiply the manifold pressure by 1.5. With the burner firing, use an analyzer
and slowly increase the gas pressure up to the new calculated high pressure cutoff point. If the
CO level reaches 400 ppm before the newly calculated setting, then at the point just before 400
ppm CO is reached is where the high gas pressure switch must be set.
•
Reset the manifold pressure back to the correct setting.
•
After the High Gas Pressure Switch is set, the recalculate the low gas pressure switch setting by
dividing the actual manifold pressure by 2 and adding the pressure drop across the valve. With
the burner firing use an analyzer and slowly decrease the gas pressure into the valve to the new
calculated low pressure cutoff point. If the CO reaches 400 ppm before the newly calculated
setting, then at the point just before 400 ppm CO is reached is where the low gas pressure switch
must be set.
Reset the incoming pressure back to the correct setting.
•
If the combustion does not reach the 400 ppm mark at the set points, the burner can be left at those
settings. IMPORTANT: Any switch can be adjusted, as long as it meets both sets of criteria: Not
greater than 400 ppm CO and meets the appropriate calculation for the switch.
Table 4: Pressure Switch Settings
Inlet Press.
Manifold Press.
T
P
6.9"
5.5"
6.9"
5.5"
8.6"
9.2"
Pressure Switch Settings
Initial setting of the High Gas Pressure Switch:
Initial setting of the Low Gas Pressure Switch:
T
> 50% T
M
T
LPS
M
3.3"
1.6+1=2.6"
4"
2+1=3"
3.3"
1.6+1=2.6"
4"
3"
3.7"
1.85+1=2.85"
2.3"
2.2"
+ ∆P*
<1.5 x T
M
M
HPS
3.3x1.5=4.9"
4x1.5=6"
3.2x1.5=4"
4"
5.6"
3.4"
8
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