Smith Cast Iron Boilers GB200 SERIES manual 8

FIGURE 2.7: GAS PIPE SIZING TABLES & EXAMPLE

Maximum Capacity of Pipe in Cubic Feet of Natural Gas per Hour for Gas Pressures of

0.5Psig or Less and a Pressure Drop of 0.3 Inch Water Column (Based on a 0.60 Specific Gravity Gas)

	Nominal							Length of Pipe, Feet
Iron Pipe		Internal
	Size,	Diameter,	10	20	30	40	50	60	70	80	90	100	125	150	175	200
	Inches	Inches
1/4"		.326	32	22	18	15	14	12	11	11	10	9	8	8	7	6
3/8"		.493	72	49	40	34	30	27	25	23	22	21	18	17	15	14
1/2"		.622	132	92	73	63	56	50	46	43	40	38	34	31	28	26
3/4"		.824	278	190	152	130	115	105	96	90	84	79	72	64	59	55
1"		1.049	520	350	285	245	215	195	180	170	160	150	130	120	110	100
1-1/4"		1.380	1,050	730	590	500	440	400	370	350	320	305	275	250	225	210
1-1/2"		1.610	1,600	1,100	890	760	670	600	560	530	490	460	410	380	350	320
2"		2.067	3,050	2,100	1,650	1,450	1,270	1,150	1,500	990	930	870	780	710	650	610
2-1/2"		2.469	4,800	3,300 2,700		2,300	2,000	1,850	1,700	1,600	1,500	1,400	1,250	1,130	1,050	980
3"		3.026	8,500	5,900	4,700	4,100	3,600	3,250	3,000	2,800	2,600	2,500	2,200	2,000	1,850	1,700
	4"	4.026	17,500	12,000	9,700	8,300	7,400	6,800	6,200	5,800	5,400	5,100	4,500	4,100	3,800	3,500

Maximum Capacity of Pipe in Thousands of Btu per Hour of Undiluted Liquefied

Petroleum Gases (at 11 Inches Water Column Inlet Pressure)

(Based on a Pressure Drop of 0.5 Inch Water Column)

Nominal						Length of Pipe, Feet
Iron Pipe
Size,
	10	20	30	40	50	60	70	80	90	100	125	150
Inches
1/2"	275	189	152	129	114	103	96	89	83	78	69	63
3/4"	567	393	315	267	237	217	196	185	173	162	146	132
1"	1071	732	590	504	448	409	378	346	322	307	275	252
1-1/4"	2205	1496	1212	1039	937	834	771	724	677	630	567	511
1-1/2"	3307	2299	1858	1559	1417	1275	1180	1086	1023	967	866	787
2"	6221	4331	3465	2992	2646	2394	2205	2047	1921	1811	1606	1498

Example: Boiler Model GB200-4H is to be installed. The distance from the existing gas meter to the installation site is 30 ft. What pipe size must be used? The local utility indicates the heating value of natural gas being supplied is 1000 Btu per cu.ft. Determine cubic feet of gas per hour for above boiler model:

135,000 Btu per hour = 135 cu.ft. per hour

1000 Btu per cu.ft.

1.Find 30 ft. in upper portion of the table for natural gas under "Length of Pipe, Feet" heading.

2.Moving down the column, match required capacity. Higher capacity is acceptable. In our case it is 152 cu.ft.

3.Move to left-hand column "Nominal Iron Pipe Size, Inches," to read required pipe size. In our case it is 3/4".

Testing Gas Piping

DANGER: Before placing gas piping into service, carefully test it to assure every joint is gas tight. Bubble test all joints with a soap solution. NEVER TEST WITH AN OPEN FLAME AS FIRE OR EXPLOSION WILL RESULT.

For any pressure testing in excess of 1/2 psi, the boiler and its individual shutoff valve must be isolated from the piping system by disconnecting them and capping the outlet(s). For any pressure testing equal to or less than 1/2 psi, the boiler must be isolated from the piping system by closing its manual shutoff valve.

Minimum pressure required at the gas valve inlet is 5" W.C. for natural gas and 11" W.C. for propane. Maximum pressure allowable at the gas valve inlet is 12" W.C. If the gas pressure is above these limits, a pressure regulator must be installed. If the gas pressure is below these limits, contact the local utility.

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