A gas piping section must carry 220 cubic feet per hour at a design length of 100 feet. Use these supplied capacities: at 7 inches water column with a 0.5-inch water-column drop, 1-inch pipe carries 175 cubic feet per hour and 1-1/4-inch pipe carries 360; at a delivery pressure of 1/2 psi with a 1.0-inch water-column drop, 3/4-inch pipe carries 240 cubic feet per hour and 1-inch pipe carries 450. After conversion to the stated 1/2 psi system with line regulators ahead of the appliances, what is the smallest pipe size demonstrated to meet the demand by the supplied capacities?
- A1-1/4 inch, because the 7 inch water column table still governs and 1-inch pipe carries only 175 there
- B1 inch, because a section carrying 220 cubic feet per hour may never be smaller regardless of pressure
- C1/2 inch, because raising the delivery pressure doubles the capacity of every size in the table
- 3/4 inch, because at the 1/2 pound delivery pressure that size is rated for 240 cubic feet per hour
Where to look it up
Explicit exercise assumptions; not a universal code requirement.
Why D is correct
Use the supplied capacities for the converted system. A 3/4-inch pipe carries 240 cubic feet per hour, exceeding the required 220 by 20. The supplied 1-inch capacity also passes but uses a larger pipe. No capacity is supplied for 1/2-inch pipe, so these data cannot justify selecting it. The 7-inch-water-column values describe different conditions. This is a comparison of the given data, not an independently verified sizing table; actual design also requires the correct material, gas, pressure, length and regulator requirements.