GM9S80 Service Manual
SCHEDULED MAINTENANCE
28
5. Use this formula to verify the Cubic Feet per Hour (CFH) input determined in step 4 is correct:
(3600 x Gas Meter Dial Size) / Time (seconds) = Cubic Feet per Hour (CFH)
3600 is used as there are 60 seconds in
a minute and 60 minutes in an hour.
60x60=3600
6. Check with your local utility for actual BTU content (caloric value) of natural gas in the area (the average is 1025
BTU’s).
7.
8.
increase pressure and input, and upward (counterclockwise) to decrease pressure and input. A properly operating unit
must have the BTU per hour input and CFM of air, within the limits shown to prevent short cycling of the equipment. As
rise limitation.
The unit being tested takes 40 seconds for the 1 cubic foot dial to make one complete revolution. Using the chart, this trans-
lates to 90 cubic feet per hour. Based upon the assumption that one cubic foot of natural gas has 1,025 BTU’s (Check with
your local utility for actual BTU content), the
90,000 BTU/HR
92,250 BTU/HR
This example is within the 5% tolerance input and does not need adjustment.
To adjust the pressure regulator on the gas valve, turn down (clockwise) to increase pressure and input, and out (counter-
clockwise) to decrease pressure and input.
propane are calculated for 2500 BTU per cubic foot gas and with proper inlet pressures and correct piping size, full capacity
will be obtained.
With propane gas, no unit gas valve regulator is used; however, the second stage supply line pressure regulator should be
-
face.
the motor and blower (belt drive).
A properly operating unit must have the BTU per hour input and CFM of air, within the limits shown to prevent short cycling
for temperature rise limitation.