Gas piping and pressures – Thomas & Betts RGM 405 User Manual
Page 13
Mfg No. 164771, Page 13
Sizing a Gas Supply Line
9. Gas Piping and Pressures
WARNING: This appliance is equipped for a
maximum gas supply pressure of 1/2 pound, 8
ounces, or 14 inches water column. Supply
pressure higher than 1/2 pound requires
installation of an additional lockup-type service
regulator external to the unit.
PRESSURE TESTING SUPPLY PIPING
Test Pressures Above 1/2 PSI: Disconnect the heater and manual
valve from the gas supply line which is to be tested. Cap or plug the
supply line.
Test Pressures Below 1/2 PSI: Before testing, close the manual
valve on the heater.
All piping must be in accordance with requirements outlined in the
National Fuel Gas Code ANSI Z223.1a (latest edition) or CAN/CGA-
B149.1 and B149.2 (See Paragraph 1). Gas supply piping installation
should conform with good practice and with local codes.
Unit heaters are orificed for operation with natural gas having a heating
value of 1000 (± 50) BTUH per cubic ft or propane gas with a heating
value of 2550 BTUH per cubic ft. If the gas at the installation site does
not meet these specifications, consult the factory for proper orificing.
Pipe joint compounds (pipe dope) shall be resistant to the action
of liquefied petroleum gas or any other chemical constituents of
the gas being supplied.
Install a ground joint union and manual shutoff valve upstream of the
unit control system as shown in Figure 13. The 1/8" plugged tapping in
the shutoff valve provides connection for a supply line pressure test
gauge. The National Fuel Gas Code requires the installation of a trap
with a minimum 3" drip leg. Local codes may require a minimum drip
leg longer than 3" (typically 6"). Bleed gas lines of trapped air.
Gas connection is either 1/2" or 3/4" depending on size and type of gas.
S i z e
Gas
Gas Connection
150-200
Natural
1/2"
250-400
Natural
3/4"
150-400
Propane
1/2"
Leak-test all connections by brushing on a leak-detecting solution.
WARNING: All components of a gas supply
system must be leak tested prior to placing
equipment in service. NEVER TEST FOR
LEAKS WITH AN OPEN FLAME. Failure to
comply could result in personal injury, property
damage or death.
Manifold or Orifice Pressure Settings
Measuring manifold gas pressure cannot be done until the heater is in
operation. It is included in the steps of the "Check-Test-Start" proce-
dure in Paragraph 22. The following warnings and instructions apply.
WARNING: Manifold gas pressure must never
exceed 3.5" w.c. for natural gas or 10" w.c. for
propane gas.
For Natural Gas: Manifold gas pressure is regulated by the combina-
tion valve to 3.5" w.c. Inlet pressure to the valve must be a minimum of
5" w.c. or as noted on the rating plate and a maximum of 14" w.c.
For Propane Gas: Manifold gas pressure is regulated by the combina-
tion valve to 10" w.c. Inlet pressure to the valve must be a minimum of
11" w.c. and a maximum of 14" w.c.
Before attempting to measure or adjust manifold gas pressure, the inlet
From Gas Supply
From
Gas
Supply
6 Drip Leg
NOTE:
Connections
shown are by
the installer.
To Controls
Manual
Gas Valve
Immediately upstream of the gas
supply connection, install a manual
shutoff valve with a 1/8 NPT
plugged tap accessible for test
gauge connection.
Ground Joint Union
Figure 13 -
Supply Piping
Connection
Capacity of Piping - Cubic Feet per Hour based on 0.3" w.c. Pressure Drop
Specific Gravity for Natural Gas -- 0.6 (Natural Gas -- 1000 BTU/Cubic Ft)
Specific Gravity for Propane Gas -- 1.6 (Propane Gas -- 2550 BTU/Cubic Ft)
Length
Diameter of Pipe
of 1/2"
3/4"
1"
1-1/4"
1-1/2"
2"
Pipe
Natural Propane Natural Propane Natural Propane Natural Propane Natural Propane Natural Propane
20’
92
56
190
116
350
214
730
445
1100
671
2100
1281
30’
73
45
152
93
285
174
590
360
890
543
1650
1007
40’
63
38
130
79
245
149
500
305
760
464
1450
885
50’
56
34
115
70
215
131
440
268
670
409
1270
775
60’
50
31
105
64
195
119
400
244
610
372
1105
674
70’
46
28
96
59
180
110
370
226
560
342
1050
641
80’
43
26
90
55
170
104
350
214
530
323
990
604
90’
40
24
84
51
160
98
320
195
490
299
930
567
100’
38
23
79
48
150
92
305
186
460
281
870
531
125’
34
21
72
44
130
79
275
168
410
250
780
476
150’
31
19
64
39
120
73
250
153
380
232
710
433
175’
28
17
59
36
110
67
225
137
350
214
650
397
200’
26
16
55
34
100
61
210
128
320
195
610
372
Note: When sizing supply lines, consider possibilities of future expansion and increased requirements.
Refer to National Fuel Gas Code for additional information on line sizing.