Modine Manufacturing DJE Installation And Service Manual page 11

C C H H E E C C K K I I N N G G I I N N P P U U T T R R A A T T E E
2. Start the furnace and determine the number of seconds it
takes to consume 1 cu. ft. of gas. Two basic formulas are
useful:
F1 = 3600 C/T
F2 = F1/C
where
F1 = input to heater, Btuh
F2 = input to heater, cu. ft. per hr.
C = calorific value of gas, Btu per cu. ft.
T = time to consume 1 cu. ft. of gas in sec.
The calorific value of gas may be determined from the local
utility or gas dealer.
These are representative values:
G G a a s s
Natural
Propane
3. If the seconds for 1 cu. ft. are more (input less) than
shown on Table 4 for model being tested, remove the cap
from the pressure regulator and take one clockwise turn
at a time on the adjustment screw until the correct time is
obtained. If the seconds are less (input greater) than
indicated in the table, follow the same procedure in a
counter-clockwise direction. Never remove adjustment
screw from regulator.
If the correct number of seconds cannot be obtained without
exceeding the limitations given above, then re-orificing is
necessary. Correct orifices can be obtained from the factory.
When requesting orifices, state type of gas, Btu content, and
its specific gravity. Also give model number of duct furnace.
For example, if the input to the furnace is 100,000 Btu and the
calorific value of gas is 1000 Btu per cu. ft., then, by the
second formula, the input is 100 cu. ft. per hr. Table 4 indicates
the time for one revolution of various size meter dials with
various input rates. If a 1 cu. ft. meter dial is used, we proceed
down the cu. ft. column to 100 cu. ft. per hr. and then
horizontally to the left to determine a time of 36 seconds for
one revolution of the dial. See Table 4 similarly, if the 1/2 cu. ft.
dial is used, we determine a time of 18 seconds for one
revolution at the required input.
(B) Pressure Method
The pressure method determines input by measuring the
pressure of the gas in the manifold in inches of water.
1. Determine orifice size from Table 5 and check actual
orifice size (s) in unit.
2. Close manual valve.
3. Remove the 1/8" pipe plug in automatic valve and attach
water manometer or "U" tube which is at least 12" high.
(See Figure 10).
4. Open manual valve and start unit.
B B t t u u p p e e r r c c u u . . f f t t . .
1000-1150
2500
5. If pressure as indicated by "U" tube is not more than 1/2"
higher or lower than indicated in Table 5, adjust regulator
as described under "Meter-Timing Method," Step 3.
If pressure as indicated by "U" tube is more than 1/2" higher or
lower than indicates in Table 5, check main line gas pressure
at input. Adjust main gas regulator to supply 6 to 7 inch W.C.
on pressure to unit regulator on natural gas and 11-14" W.C.
on propane gas.
F F i i g g u u r r e e 1 1 0 0 - - C C h h e e c c k k i i n n g g M M a a n n i i f f o o l l d d P P r r e e s s s s u u r r e e
w w i i t t h h " " U U " " T T u u b b e e
U-TUBE
SERIAL
PLATE
F F i i g g u u r r e e 1 1 1 1 - - D D i i a a l l s s o o f f T T y y p p i i c c a a l l G G a a s s M M e e t t e e r r
LIMIT
SWITCH
GAS VALVE
FITTING
1 1 1 1