Neb. Rev. Stat. § 48-408
Every such wheel six inches or less in diameter shall be provided with a three-inch suction pipe; wheels six inches to twenty-four inches in diameter, with a four-inch suction pipe; wheels from twenty-four inches to thirty-six inches in diameter, with a five-inch suction pipe; and every wheel exceeding thirty-six inches in diameter shall be provided with a suction pipe not less than six inches in diameter.
The suction pipe from each wheel shall be of full size to its terminus, and a suction pipe to which smaller pipes are attached shall, in its capacity, be equal to the combined capacities of all smaller pipes attached thereto, and the discharge pipe shall be of as large capacity as, or larger capacity than, the combined capacities of all suction pipes.
Neb. Rev. Stat. § 48-408