Rheem GF951U Series - Page 37

37
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adjustments is 5⬙ w.c. for natural gas,
however 6⬙ to 7⬙ is recommended.
The minimum supply pressure is 11⬙
w.c. for LP gas.
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To check for gas leakage, use an
approved chloride-free soap and
water solution, an electronic com-
bustible gas detector (see Figure 38),
or other approved method.
GAS VALVE
This furnace has a 24-volt operated
valve. It has ports for measuring
supply pressure and manifold
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The T-valve should be readily
accessible to turn the gas supply on
o
r off. Install a drip leg in the gas
supply line as close to the furnace as
possible. Always use a pipe
compound resistant to the action of
liquefied petroleum gases on all
threaded connections.
!%('*,&, When making gas pipe
connections, use a back-up wrench to
prevent any twisting of the control
assembly and gas valve.
Any strains on the gas valve can
change the position of the gas orifices
in the burners. This can cause erratic
furnace operation.
!%('*,&, Do not run a flexible
gas connector inside the unit. If local
codes allow the use of a flexible gas
appliance connector, always use a
new listed connector. Do not use a
connector which has previously
serviced another gas appliance.
Massachusetts law requires that all
flexibile connectors be less than 36ⴖ.
The gas pipe gasket in the cabinet
does not seal around a flexi-ble gas
connector. !F;E;?BADF3@FFA:3H73>>
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!%('*,&, ENSURE that the
furnace gas control valve not be
subjected to high gas line supply
pressures.
DISCONNECT the furnace and its
individual shut-off valve from the gas
supply piping during 3@KBD7EEGD7
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GAS PRESSURE
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13//+6/0&1130&1).3+%#&2.
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!&+,$$,!'&+Q', !+''#
'*!&+,*-,!'&+
The minimum supply pressure to the
gas valve for proper furnace input
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Capacity of gas pipe of different diameters and lengths in cu. ft. per hr. with pressure drop of 0.3 in. and specific
gravity of 0.60 (natural gas).
Nominal Length of Pipe, Feet
I
ron Pipe
S
ize, Inches 10 20 30 40 50 60 70 80
1/2 132 92 73 63 56 50 46 43
3
/4 278 190 152 130 115 105 96 90
1 520 350 285 245 215 195 180 170
1
-1/4 1,050 730 590 500 440 400 370 350
1-1/2 1,600 1,100 890 760 670 610 560 530
A
fter the length of pipe has been determined, select the pipe size which will provide the minimum cubic feet per hour
required for the gas input rating of the furnace. By formula:
Gas Input of Furnace (BTU/HR)
C
u. Ft. Per Hr. Required =
H
eating Value of Gas (BTU/FT
3
)
The gas input of the furnace is marked on the furnace rating plate. The heating value of the gas (BTU/FT3) may be
d
etermined by consulting the local natural gas utility or the LP gas supplier.
pressure. The valve body contains a
pressure regulator to maintain proper
manifold pressure.
A manual control is on the valve
body. It can be set to only the P'&Q
or P'Q positions. The gas valve is
a slow-opening valve. See Figure 39.
When energized, it takes 6 to 8
seconds to fully open.
!
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