Raypak 408 Installation And Operation Manual page 17

Figure 16. Robertshaw 7000 DERHC (Heater Model 408)
Gas Pressure Adjustment
Figure 17. Honeywell VR8304 (Heater Models 268 and 408)
5.6.4. Pipe Sizing for Gas Connection
These capacities shown below based on using SCH 40
black iron pipe. For capacities using other materials,
consult local code.
Input 3/4"
Model
(KBTU) N P
15 35
268 266.0
(5) (11)
15
408 399.0 *
(5)
3
Natural Gas 1000 BTU/FT 0.60 specific Gravity @ 0.5 in. WC Pressure Drop
3
Propane Gas 2500 BTU/FT 1.53 specific Gravity @ 0.5 in. WC Pressure Drop
* A 3/4" gas line can be used for up to 5' (1.5 m) maximum length from the gas valve
in addition to the sediment trap.
Table H. Maximum Equivalent Pipe Length (ft/m)Flow
Rates
Gas Pressure Adjustment
1" 1-1/4" 1-1/2"
N P N P N
50 125 210 480 445
(15) (38) (64) (146) (136)
20 55 95 225 215
(6) (17) (29) (69) (66)
Model
268 1-1/4"–1-1/2" - 2"
408 1-1/4"–1-1/2" - 2"
* When flow rates exceed maximum GPM (lpm) an external auxiliary bypass valve
is required. See external bypass valve section for details.
Table I. Flow Rates
Figure 18. External Bypass Valve
Flow
GPM (lpm)
30 (114)
40 (151)
50 (189)
60 (227)
70 (265)
80 (302)
90 (341)
100 (378)
P
Table J. Heat Exchanger Pressure Drop
480
(146)
Min. GPM
Pipe Size
(lpm)
25 (95)
40 (151)
Pressure Drop (Ft of Head)
268
8.0
9.0
9.8
10.5
11.0
11.5
14.0
17.0
Max. GPM*
(lpm)
125 (473)
125 (473)
408
9.0
9.8
10.5
11.0
11.5
14.0
17.0
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