Figure 4a. Quick approximation for downstream pipe size.
Outlet Pressure
Zero
32 osi
8 osi
16 osi
Accurate calculation for downstream pipe size per Figure 4b.
0
2 ½ "
2"
2 ½ "
2"
10 000 20 000 30 000 40 000
1. Determine maximum allowable pressure drop (ΔP D ) downstream of 7335. ΔP D = 7335 outlet pressure minus pressure required at inlet of gas flow control device. 2. Start with downstream pipe size indicated in Figure 4a. Using that pipe size, determine equivalent length (L D ) of pipe and fittings between 7335 and gas flow control device. (For equivalent lengths of valves and fittings, see Table 5.22 in North American COMBUS- TION HANDBOOK) 3. Correct ΔP D ÷ L D to 100 equivalent feet of pipe: ΔP D ÷ L D /100 = ΔP 100 . 4. On Figure 4b, locate maximum cfh natural gas pipe must carry, read across to (diagonal) pipe size line, then down to pressure drop per 100 equivalent feet of pipe. If result is less than ΔP 100 , pipe is sufficient. If result exceeds ΔP 100 pipe is undersized--repeat procedure for larger sizes until a satisfactory pressure drop results.
3"
3"
3"
4"
3"
4"
50 000
4"
60 000 70 000 80 000 90 000 100 000
6"
4"
6"
6"
150 000
8"
6"
8"
200 000
8"
10"
Figure 4b. Accurate evaluation for downstream pipe size.
150 000
100 000
50 000
25 000
10 000
0.5
1.0
2
3 4 5
10
20
30 40 50
100
200 300
500
Pressure drop, osi per 100 equivalent feet of pipe
Bulletin 7335 Page 5
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