Form RZ-NA-I-FT, Page 10
12. Gas Pressures (cont'd)
Sizing a Gas
Supply Line
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 21. The following warnings and instructions apply.
WARNING: Manifold gas pressure must never exceed
3.5" w.c. for natural gas and 10" w.c. for propane
gas.
For Natural Gas:
When the heater leaves the factory, the combination
gas valve is set so that the manifold gas pressure is regulated to 3.5"
w.c. Inlet supply pressure to the valve for natural gas must be a mini-
mum of 5" w.c. or as noted on the rating plate and a maximum of 14"
w.c.
For Propane Gas:
When the heater leaves the factory, the combina-
tion gas valve is set so that the manifold gas pressure is regulated to
10" w.c. Inlet supply pressure to the valve for propane gas 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
supply pressure
must
be within the specified range both when the heater
is in operation and on standby. Incorrect inlet pressure could cause
excessive manifold gas pressure immediately or at some future time. If
natural gas supply pressure is too high, install a regulator in the supply
line before it reaches the heater. If natural gas supply pressure is too
low, contact your gas supplier.
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 8 -
Supply Piping
Connection
Instructions on How to Check Manifold
Pressure (can only be done after heater is
installed):
1)
With the manual valve positioned to prevent flow to the main burn-
ers, connect a manometer to the 1/8" pipe outlet pressure tap in the
valve. NOTE: A manometer (fluid-filled gauge) is recommended rather
than a spring type gauge due to the difficulty of maintaining calibra-
tion of a spring type gauge.
2)
Open the valve and operate the heater. Measure the gas pressure to
the manifold. Normally adjustments should not be necessary to the
factory preset regulator.
If adjustment is necessary, set pressure to correct settings by turning
the regulator screw IN (clockwise) to increase pressure. Turn regulator
screw OUT (counterclockwise) to decrease pressure.
Derating by Manifold Pressure Adjustment for
High Altitude Operation
If the heater is being installed above 2000 ft (610M) and it was deter-
mined in Paragraph 4 that derating by manifold pressure adjustment is
permissible, follow the instructions below.
Instructions for Derating a Heater by Adjusting Manifold
Pressure (The heater must have a single-stage gas valve
and must be factory-equipped for sea level operation.)
1. Check the rating plate to be certain that the heater is equipped for
sea level operation.
Do not attempt to derate by manifold gas pres-
sure adjustment if the heater is factory equipped for high alti-
tude. Do not attempt to adjust manifold pressure on heaters
equipped with two stage gas valves.
2. Determine the required manifold pressure for the elevation where
the heater will be operating. If unsure of the elevation, contact the
local gas supplier.
Manifold Pressure Settings by Elevation
Altitude
Natural Gas
Propane Gas
Feet
Meters
(inches W.C.) (inches W.C.)
0- 2000
1-610
3.5
10.0
2001-3000
611-915
2.8
7.7
3001-4000
916-1220
2.5
7.1
4001-5000
1221-1525
2.3
6.4
5001-6000
1526-1830
2.1
5.8
6001-7000
1831-2135
1.9
5.2
7001-8000
2136-2440
1.7
4.6
8001-9000
2441-2745
1.5
4.1
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)
Sp ecific Gravity for Prop ane Gas -- 1.6 (Prop ane 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 sup ply lines, consider p ossibilities of future expansion and increased requirements.
Refer to National Fuel Gas Code for additional information on line sizing.